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Urban Water JournalPublication details including instructions for authors and subscription informationhttpwwwtandfonlinecomloinurw20

Urban water management strategies based on a totalurban water cycle model and energy aspects ndash Casestudy for Tel AvivTong Thi Hoang Duong a Avner Adin b David Jackman c Peter van der Steen a amp KalaVairavamoorthy aa UNESCO-IHE Institute for Water Education PO Box 3015 2601 DA Delft The Netherlandsb Department of Soil amp Water Sciences The Hebrew University of Jerusalem PO Box 12Rehovot 76100 Israelc Mei Avivim ndash Tel Aviv-Jaffa Water Corporation 5 Philon Street Tel Aviv 64518 IsraelPublished online 08 Apr 2011

To cite this article Tong Thi Hoang Duong Avner Adin David Jackman Peter van der Steen amp Kala Vairavamoorthy (2011)Urban water management strategies based on a total urban water cycle model and energy aspects ndash Case study for Tel AvivUrban Water Journal 82 103-118 DOI 1010801573062X2010546861

To link to this article httpdxdoiorg1010801573062X2010546861

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Taylor amp Francis makes every effort to ensure the accuracy of all the information (the ldquoContentrdquo) containedin the publications on our platform However Taylor amp Francis our agents and our licensors make norepresentations or warranties whatsoever as to the accuracy completeness or suitability for any purpose of theContent Any opinions and views expressed in this publication are the opinions and views of the authors andare not the views of or endorsed by Taylor amp Francis The accuracy of the Content should not be relied upon andshould be independently verified with primary sources of information Taylor and Francis shall not be liable forany losses actions claims proceedings demands costs expenses damages and other liabilities whatsoeveror howsoever caused arising directly or indirectly in connection with in relation to or arising out of the use ofthe Content

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CASE STUDY

Urban water management strategies based on a total urban water cycle model and energy

aspects ndash Case study for Tel Aviv

Tong Thi Hoang Duonga Avner Adinb David Jackmanc Peter van der Steena and Kala Vairavamoorthya

aUNESCO-IHE Institute for Water Education PO Box 3015 2601 DA Delft The Netherlands bDepartment of Soil amp WaterSciences The Hebrew University of Jerusalem PO Box 12 Rehovot 76100 Israel cMei Avivim ndash Tel Aviv-Jaffa Water

Corporation 5 Philon Street Tel Aviv 64518 Israel

(Received 23 April 2010 final version received 7 December 2010)

Global change pressures such as climate change water scarcity population growth full urbanisation of catchmentsand rising energy costs may increasingly affect the urban water system of Tel Aviv These challenges formed theincentive for a multidisciplinary Learning Alliance of water sector institutions to embark on a process to identifyways to improve sustainability of the cityrsquos water system Sustainability indicators were identified and a whole-of-system water balance model (AquaCycle) was used to score the indicators for future scenarios and strategiesStrategies included rainwater harvesting stormwater use permeable pavements and wastewater reuse The effect ofthe strategies on total water imported into the city was a reduction of 10 by rainwater harvesting and 32 bywastewater reuse at cluster scale The latter strategy reduced energy consumption from 289 kWh per m3 of volumeof water used (import thorn reuse) in the current situation to 245 kWh per m3

Keywords decision support integrated modeling integrated urban water performance indicators rainwaterharvesting urban water planning

1 Introduction

11 Global change pressures

Cities around the world including Tel Aviv willincreasingly face global change pressures and theireffects on the urban water cycle Global changepressures include climate change and changing pat-terns of precipitation floods and droughts populationgrowth and further urbanisation of catchmentsdeterioration of infrastructure sea level rise and risingenergy costs These pressures will make it a challengeto continue to deliver core urban water services (watersupply sanitation and flood protection) withoutincreasing the impact on the natural environmentUnless actions are taken urban water demand willcontinue to increase and therefore also quantities ofwaste water and stormwater As a result environ-mental damage and damage due to flooding is likely toincrease

There is a strong nexus between water and energysince energy is required to provide vital urban waterand wastewater services To date limited analyses ofthe energy implication of water strategies have beenundertaken and energy use is rarely mentioned inurban water strategies despite considerable public

commitment and efforts from individual utilitiesIssues associated with the links between climateenergy and water will become more critical in thefuture As a consequence planners must now considerthe energy implications in decision making on thewater system (Kenway et al 2008)

12 Introduction Tel Aviv and local pressures

Tel Aviv has developed into a modern city of 394940inhabitants in 179518 households (Statistical Year-book 2007) occupying an area of 52 km2 with apopulation density of 7200 personskm2 The annualgrowth rate of the population is lately 22 There are225919 housing units (residential and non-residential)for a total floor area of 24252000 m2 As a Medi-terranean seashore city the climate in Tel Aviv is mildand the average annual rainfall is about 530 mmLowest daily average temperature (in January) is 968Cand the highest average daily temperature (in August)is 3028C Tel Aviv is a wealthy city compared to thenational average and is the commercial centre of Israelwith an estimated 400000 of non-resident visitors perday for shopping work or other business

Corresponding author Email pvandersteenunesco-iheorg

Urban Water Journal

Vol 8 No 2 April 2011 103ndash118

ISSN 1573-062X printISSN 1744-9006 online

2011 Taylor amp Francis

DOI 1010801573062X2010546861

httpwwwinformaworldcom

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The drinking water is supplied to the city mainly bythe national water company Mekorot (41 million cubicmetre per year MCMY or 90 of the total supply)through the National Water Carrier (NWC) TheNWC is an integrated national distribution networkthat is fed from the Lake of Galilee (150 km from thecity) several aquifers and recently constructed desali-nation plants Another 10 (around 5 MCMY) issupplied from local wells by the municipality Themunicipality also maintains the pipe-lines and thewater reservoirs in the city and cares for the properwater pressures and disinfection The municipality alsooperates a separate sewer system (around 501 km ofpipes) and pumps the sewage to the WWTP (WasteWater Treatment Plant) through a central collector(Reading-Rishon) both owned by the Dan RegionAssociation of Towns (of which Tel Aviv is a member)Stormwater is collected by gravity and dischargeddirectly without treatment to the Mediterranean SeaMonitoring of and billing for water consumption isalso performed by the municipality

The Dan Region Association of Towns collects andtreats the wastewater from Tel Aviv and surroundingtowns and was established by seven municipalities (TelAviv was the major one) in the 1950s Today there are24 municipalities connected to the central WWTP andaround two million person equivalents of wastewaterare treated The treated water is transferred to theNegev desert for irrigation purposes The duties of theAssociation include the monitoring of the sources ofwastewater A specialised department visits industrialplants and other major wastewater producers in TelAviv and its surroundings to prevent pollution atsource

The major water-related pressure in Tel Aviv ispotential water scarcity as Tel Aviv is one of the largerwater consumers in an arid country that is sufferingfrom water scarcity at the country level Additionalpressures on the city such as population growthurbanisation pollution of aquifers and rise in tem-perature due to climate change may worsen thisproblem These pressures also show that the urbanwater system of Tel Aviv is not fully sustainable

13 Sustainable cities sustainable water systems

One may raise the question when are urban watersystems sustainable Or what kind of changes incurrent urban water systems are required Answeringsuch questions is strategic in order to transform citiesinto long term viable places The main objective of asustainable urban water system is to satisfy thewater related needs of the community at the lowestcost to society while minimising environmental andsocial impact (White and Turner 2003) Thus the

sustainability of the urban water system involveseconomic viability social stability and wise use ofresources and should be considered as a manner toprotect and nourish the natural environment

In order to re-orientate urban areas towardssustainability it is recognised that the different aspectsof urban water systems should be viewed in relationto each other which requires the adoption of anintegrated approach to urban water system planningservice provision and management Integrated urbanwater management takes a comprehensive approach tourban water services viewing water supply drainageand sanitation as components of an integrated physicalsystem and recognises that the physical system sitswithin an organisational framework and a broadernatural landscape (Mitchell 2006)

14 Sustainability indicators and strategic planning

To change cities towards sustainability a changeprocess is required Strategic planning is a tool thatcan be used to direct the overall development of a cityto address challenges and to benefit from opportunities(Cities Alliance 2006) The monitoring of the state of acity (an essential element of the strategic planningcycle) could be based on sustainability indicatorsSustainability indicators are pieces of informationwhich summarise important properties visualise phe-nomenons of interest quantify trends and commu-nicate them to relevant target groups (Lundin 2003)Indicators are a tool for sustainability assessment andconstruction of indicators is a major topic in sustain-ability studies (Scheller 2000)

15 Use of modelling for strategic planning

Sustainability indicators can be used for reportingbut also to evaluate different management options forthe future In this context integrated urban watersystem models can be powerful tools in exploringthe performance (in terms of indicator scores) ofalternative options such as reusendashrecycling schemes(Rozos et al forthcoming) decentralised solutions(Makropoulos et al 2008b) water demand manage-ment schemes etc A model that is taking a whole-of-system perspective is AquaCycle a model that isable to describe and predict the total quantity ofwater moving through the urban water cycle (Mitchellet al 2001) It was developed to provide a holistic viewof an urban water system allowing water supply waterdisposal and storm water to be considered ascomponents within a single framework (Mitchell2005 Karka et al 2007) Based on the AquaCycleoutcomes a number of sustainability indicators can becalculated as will be shown in this research

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The main aim of this research is to develop urbanwater management strategies by applying the Aqua-Cycle model for the investigation of their effects on thesustainability of the water system of Tel Aviv Thesustainability is measured (among others) by indicatorswhich are related to the reduction of freshwaterconsumption energy use and the increase in theamount of wastewater reuse The research is aimed atproviding valuable information for decision makers inTel Aviv to steer the city towards sustainability in asituation of water scarcity

2 Methodology

21 Integration of strategic planning and modelsupported decision making

The methodology is a combination of strategicplanning as described in the Cities Alliance Guide toCity Development Strategies (Cities Alliance 2006) andthe application of a total urban water cycle model Themodel is used to assess the current situation as well asto evaluate future scenarios and strategies (Van derSteen and Howe 2009) The process is an integration ofengineering calculations and a stakeholder involve-ment process As a first step in the process amultistakeholder platform was established which wasnamed the Learning Alliance (or lsquoWater Clubrsquo) ALearning Alliance is an (informal) group of stake-holders that in Tel Aviv jointly (1) Assesses thecurrent shape of the urban water system and for-mulates un-sustainability factors (2) Develops a visionfor the future state of the urban water system (3)Translates the vision in a set of sustainability objectivesand indicators (4) Identifies possible future scenarioswhere scenarios are defined as possible futures that areout of the control by urban water managers such asclimate change (5) Formulates strategies aimed atachieving the vision and (6) Recommends an im-plementation plan to relevant planning authorities (seeFigure 1) (Butterworth et al 2008) The LA workshopswere complemented by collection of secondary datasite visits and by interviewing water sector profes-sionals on their views on the vision scenarios andstrategies The gathered data was used to prepare theinput files for AquaCycle to make a water balance Inaddition was calculated how much energy is requiredfor the various strategies (Figure 2)

22 AquaCycle

AquaCycle is a total urban water cycle modeldeveloped to take a more holistic view allowing watersupply wastewater disposal and storm water drainageto be considered as components within a single systemThe lsquocyclersquo starts with water entering as precipitation

or as (fresh) water imported in order to meet theindoor and outdoor water use requirement The waterthen passes through the households or other waterusers and exits in the form of evapotranspirationstorm water or wastewater (Mitchell 2005) AquaCycleoperates on three different scales (unit-block clusterand catchment) (see Figure 3) in order to enable thesimulation of any urban form The input data for themodel which uses a time step of one day includesclimate data indoor water use data and site character-istics Surfaces are divided into two categoriespervious and impervious Impervious surfaces includeroofs roads and pavement Pervious areas are house-hold gardens and open public space (parks) and aremodelled as single stores that overflow when full intothe drainage system Water evaporation from bothpervious and impervious areas is calculated accordingto daily potential evapotranspiration values Theamount of water imported into an area is the sum ofindoor water use irrigation and leakage The totalwastewater discharge from the catchment is the sum ofindoor water use infiltration and inflow from thestorm water drainage system (Mitchell 2005)

The application of AquaCycle to Tel Avivrsquos watersystem involved the determination of three groups of

Figure 1 Overview of (on-going) strategic planning exercisefor the water system of Tel Aviv

Figure 2 Procedures of research methodology (numberindicates order of the steps in the process)

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data meteorological data indoor water use profile andphysical site characteristics The details about datacollection and processing are presented below

23 Meteorological data

The climate data input file is a series of dailyprecipitation and potential evaporation figures from1994 to 2007 Precipitation data of Tel Aviv wasobtained directly from the European Climate Assess-ment amp Data set project (ECAampD 2008) Potentialevaporation data was estimated based on monthlyheat indexes and the equations presented by theThornthwaite method (Thornthwaite 1948) The timeseries was used to simulate future precipitation Forthe baseline scenario the time series was assumed torepeat itself in 2009ndash2022 2023ndash2036 etc For thelsquonormal scenariorsquo the time series was used without anyadjustments from 2009 to 2022 while precipitation wasreduced by 10 for the period 2023ndash2050 andtemperature was increased by 158C for the sameperiod For the lsquoextremersquo scenario the values were 15and 258C respectively The lsquonormalrsquo scenario is basedon the climate change estimation of the Israel Ministryof Environmental Protection (2008) The lsquoextremersquoscenario was included to investigate the response of theurban water system to more extreme climate change

24 Indoor water use profile

Average yearly household water consumption figureswere obtained from the municipality as well asconsumption figures for public buildings health carehotels businesses sport facilities security transportand construction Since AquaCycle only considerslsquohouseholdsrsquo as water consumers (apart from publicirrigation) it was assumed that households areconsuming the sum of the consumption in the sectorsmentioned above These figures include the consump-tion by the day-time residents The consumption per

household was calculated by dividing that sum bythe number of households The end-use of water inhouseholds (in kitchen bathroom garden etc) is notknown for Tel Aviv and therefore the indoor waterusage profile for kitchen bathroom laundry and toiletof Canberra (Mitchell 2005) was copied and adjustedpro rata to a total household consumption ascalculated for Tel Aviv

25 Physical site characteristics

The municipal boundaries of the city were taken as thecatchment boundary The catchment was divided intosix clusters These six clusters were formed by groupingthe 37 sub-catchments of the drainage system suchthat each group of sub-catchments equalled (as muchas possible) one of the city-quarters used by theStatistics department of the municipality Informationof total area population and land use by quarter (nownamed cluster) was available from the StatisticsDepartment and was used as input data for AquaCycle(Figure 4) The road area and the open space area ineach cluster were estimated based on satellite imagesmaps of land use and detailed information from theStrategic Planning Unit of Tel Aviv Municipality(Municipality of Tel Aviv 2006)

Though the study area includes residential com-mercial and public buildings it was assumed that allbuildings are residential buildings This assumption isin line with the previous assumption on the allocationof all water consumption (except public irrigation) tohouseholds Since most of the buildings in Tel Aviv areapartment blocks the assumption seems reasonableThe typical apartment block houses several householdunits (apartments) and one apartment is equal to oneunit-block in the model The number of unit-blocks ineach cluster was calculated by dividing the totalpopulation of a cluster by the average number ofoccupants per household (22 Statistics Department)The total area of unit-blocks in each cluster was

Figure 3 Spatial scales used in AquaCycle The area of garden roof and pavement in the unit-block in the model is asmeasured for the typical multi-unit apartment block but divided by the number of apartments in the block

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calculated based on the total area of a cluster minusthe area of roads and public open spaces The averagearea of one unit-block was obtained from the total areaof unit-blocks and the number of unit-blocks withinthe cluster Physical characteristics of a representativeapartment block were estimated by observation basedon satellite images and site visits It was estimated thatthe areas of roof garden and pavement per apartmentblock are 70 15 and 15 respectively The areas wereproportionally allocated to the apartments in the blockand therefore the percentages are also valid for theunit-blocks in the model

26 AquaCycle outputs and energy calculations

The output of the model is a water balance with dailyvalues for precipitation piped water supply evapo-transpiration stormwater drainage and wastewatercollection Monthly or yearly average values can becalculated for the catchment cluster or unit-blockscale The mass balance for the catchment scale wasused to calculate the total energy consumption of thesystem All components of the water system thatconsume energy were identified by interviewing staff ofTel Aviv municipality and the Mekorot company anddata on energy consumption (mostly in kWhm3) wereobtained

27 Formulation of scenarios

Scenarios were not formulated to predict the futurebut were used by the LA as tools for thinking about

possible futures and to evaluate the impact ofdecisions taken today on these futures Commonelements in the scenarios were based on regulatorysocial economic environmental and technical aspects(Makropoulos et al 2008a) but not all of theseelements can be modelled quantitatively In thiswork four quantitative scenarios were formulatedfor Tel Aviv until the year 2050 including fourfactors precipitation temperature population growthand urbanisation all of which can be simulated byAquaCycle simulation (see Table 1) All of thesefactors impact directly or indirectly on Tel Avivrsquosurban water system via the effects on water demandwater resources water infrastructure and urban sur-face permeability The baseline scenario describes thecurrent situation of the city The lsquonormalrsquo scenario isbased on estimations on climate change by IsraelMinistry of Environmental Protection (2008) Data onhistorical population growth rate (22) was obtainedfrom Tel Aviv Municipality The scenarios assumedthe same growth rate to continue until 2050 whichwould only be possible by densification and morehigh-rise buildings in the city In all scenariosdensification leads to a reduction in (permeable) publicopen space of 20

28 Formulation of strategies

The LA developed strategies to achieve the visiongiven the possible future scenarios through groupdiscussions and by one-on-one interviews Onlystrategies that could be simulated by AquaCycle arepresented here The strategies are

A Stormwater use and temporary aquifer storage

Measures for stormwater use and aquifer infiltrationprojects were simulated for each cluster The storm-water from the unit-blocks and from the roads drainedinto a stormwater storage tank in each cluster and wasreused for toilet flushing garden and public spaceirrigation Excess stormwater was infiltrated into theaquifer The stormwater surface storage volumesinitially used were cluster 1 15000 m3 cluster 25000 m3 cluster 3 15000 m3 cluster 4 15000 m3cluster 5 5000 m3 cluster 6 5000 m3 (based on theoptimisation routine of AquaCycle) A 10000 m3 ofaquifer storage was applied for each cluster The effectof increasing and decreasing these volumes wasinvestigated as well

B Rainwater harvesting

A rainwater tank of various sizes was applied atevery household in all clusters of the city Rain

Figure 4 Clusters defined for the Tel Aviv catchment(Numbers 1ndash6) and Tel Avivrsquos neighbouring municipalities

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water was used in the kitchen for laundry inthe bathroom for toilet flushing and for gardenirrigation

C Permeable pavement

Pavements in unit-block gardens and for roads werereplaced by permeable pavements simulated in Aqua-Cycle by increasing the garden and open space area inthe city

D Wastewater reuse at unit-block scale

Decentralised wastewater treatment units were appliedat every household in the city Wastewater fromkitchen bathroom and laundry was treated and reusedfor toilet flushing and garden irrigation It wasassumed that no water was lost in the treatmentprocess The storage volume for treated wastewater atevery household in each cluster was identified accord-ing to the optimisation results of AquaCycle (200 L ofwastewater storage per household in cluster 1 2 3 56 and 100 L of wastewater storage in cluster 4)

E Wastewater reuse at cluster scale

Wastewater treatment units were applied for eachcluster Household wastewater draining to a clusterwastewater storage tank was treated stored andsupplied for toilet flushing and garden irrigation forhouseholds and for open space irrigation It wasassumed that no water was lost in the treatmentprocess The treated wastewater storage volumes werecluster 1 7900 m3 cluster 2 4700 m3 cluster 38300 m3 cluster 4 1300 m3 cluster 5 9100 m3cluster 6 7200 m3 (based on the optimisation routineof AquaCycle)

29 Evaluation of strategies

As mentioned above the LA developed a vision for asustainable urban water system for the city This visionwas translated into tangible objectives the achieve-ment of which can be measured by sustainabilityindicators The score for these indicators were used toevaluate the strategies rather than by a thoroughengineering and economic feasibility study Some ofthe indicators could be evaluated in a quantitative wayusing the AquaCycle outputs others were evaluatedqualitatively

3 Results and discussion

31 Sustainability objectives and indicators

Based on interviews and general investigations it wasfound that the urban water system of Tel Aviv istypical for an advanced developed country but alsocharacterised by a number of un-sustainability factorswhich need improvement With regard to planning ofthe whole system it was noticed that lsquowater manage-mentrsquo is not addressed in the Strategic Plan of the city(Municipality of Tel Aviv 2006) and water indicatorsare therefore also not included in the set of indicatorsthat is used to monitor the development of the cityThis is somewhat surprising since the domestic waterconsumption in the city is higher than the amount thatcan be sustained from renewable water sources Thewater supply system is also threatened by insufficientmaintenance of the distribution system which causesbio-film growth and microbial pollution which in turnmay cause a higher chlorine demand One of theunderlying causes of the poor maintenance is lack ofsuitable financial resources for local government tomaintain the drinking water quality The same reasonsalso result in frequent leakages from the sewer system

Table 1 Formulated scenarios and factors until the year 2050

FactorPrecipitationdecrease

Temperatureincrease

Populationgrowth rate Urbanisation

Baseline scenario ndash ndash 22lsquoNo major changersquo scenario ndash ndash 22 20 of public open space is replaced

by residential area (10 in 2022 andanother 10 in 2046) road area isnot changed

lsquoNormalrsquo scenario 20 158C 22 20 of public open space is replacedby residential area (10 in 2022 andanother 10 in 2046) road area isnot changed

lsquoExtremersquo scenario 30 258C 22 20 of public open space is replacedby residential area (10 in 2022 andanother 10 in 2046) road area isnot changed

From 2023 onwards

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which causes severe pollution of the local aquiferwhich is one of the drinking water sources for the cityBasically all municipal wastewater is collected andtreated to a tertiary level but it is not utilised foragricultural irrigation within the region but in theNegev Urban parks in Tel Aviv are still irrigated withfresh water Stormwater is collected in a separatedrainage system but discharged directly to the seawithout any treatment There is no monitoring systemor research to evaluate the amount of stormwatergenerated in the city and its quality It is likely that TelAviv is overlooking the potential to use this nonconventional water resource The capacity of thedrainage system is not sufficient to prevent occasionalflooding Finally the un-sustainability of the systembecomes clear from the significant amount of energyused to transport fresh water over long distances anduphill (from the Sea of Galilee) to treat wastewater inan energy intensive system and finally to pump effluentto irrigation fields in the south of the country Thecommissioning of desalination plants will only increasethe energy consumption in the system

Based on this assessment the LA formulated aVision for sustainable urban water management in TelAviv lsquoTel Avivrsquos water system management will beestablished based on sustainability indicators andapply an efficient and integrated water managementto meet the water demand of citizens and for otherapplications with sufficient qualities and reasonableprices while the natural status of water resources isassuredrsquo The vision was translated into a set oftangible objectives and related indicators as shownin Table 2

32 Model calibration and simulation of wastewateroutput

The characteristics of the modelled clusters and therepresentative unit-block are outlined in Table 3 and 4The meteorological data the indoor water use profileand physical site characteristics were used as inputsfor the model The default calibration parameters(Table 5) initially were used and the model output interms of lsquoimported waterrsquo was compared with themunicipalities measured data on total water distrib-uted to the consumers The average amount oflsquoimported waterrsquo simulated by the model was about10 lower than the total water consumption Thelsquotrigger to irrigatersquo is the fraction of the optimal soilmoisture for plant growth which is still acceptable tothe user This trigger for private gardens and publicopen space was adjusted to 062 and as a result theaverage lsquoimported waterrsquo simulated by the model thenwas exactly the average volume of water distributed tothe consumers (Figure 5)

The monthly water consumption in the city isabout 40 higher in the summer irrigation seasonthan in the winter season The seasonal fluctuationcould be described well by the model throughirrigation of private gardens and public open spaceIt is likely that also the indoor water use is higher insummer but it is not possible in AquaCycle to changethe household indoor water consumption between theseasons Variation in imported water based on thefigures provided by the municipality (Figure 5) isrelatively large between some of the summer monthsespecially in 2004 and 2007 The reason for these largerfluctuations is unknown since the differences intemperature and potential evapotranspiration do notseem to explain such large fluctuations The model istherefore also not able to describe well these short-termfluctuations

Further calibration of the model was attemptedon observed wastewater flows from the wider TelAviv area (the Dan District) Unfortunately thewastewater flow from Tel Aviv is not measuredseparately from the wastewater flow from surround-ing municipalities It was therefore assumed that theamount of wastewater production per capita per yearin the various municipalities in the Dan District is thesame Therefore based on the population of TelAviv the amount of wastewater generated from TelAviv is estimated as 326 of total wastewaterproduction of the Dan District The wastewater flowssimulated by AquaCycle in the dry season (AprilndashOctober) were 18 lower than the flows based onmeasurements and the above described calculation(Figure 6) The simulated values may actually becloser to reality since the simulated values are90 of the indoor water consumption (about 31MCMmonth Figure 5) whereas the measured value(adjusted for population) is more than the actualindoor water consumption The higher flows inJanuary March and December are caused by wrongconnections between the stormwater drainage andfoul sewerage system The observed increase due tostormwater infiltration could be used to adjust thecalibration parameter lsquo of surface runoff as inflowrsquo(Table 5) The default value is 3 but a better fitwas achieved by using 7 This percentage is similarto the estimate of infiltration by Mekorot theoperator of the treatment plant (Aharoni personalcommunication)

33 The water balance of the system

The calibrated model was used to prepare the averageannual water balance for the city for the years2003ndash2007 (Figure 7) The water balance can be usedfor a fundamental evaluation of the sustainability of

Urban Water Journal 109

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Table

2

Specificobjectives

andsustainabilityindicators

fortheurbanwatersystem

ofTel

Aviv

Specificobjective

Indicator

Unit

WaterPolicy

1TA

willraiseawarenessamongitscitizensabout

lsquowaterandsustainabilityrsquoandwillinvolvethe

publicin

decisionmaking

Thenumber

ofcitizensthatwillparticipate

inconsultativemeetings

Number

ofcitizensper

year

2TA

willmanageitsurbanwatersystem

inan

integratedwayintegratingaspects

ofwater

supplystorm

wateramp

wastew

atermanagem

ent

Theproductionofanintegratedurbanwater

managem

entplanforthecity

at2-yearintervals

Tim

elyproductionofintegratedplan

3A

setofsustainabilityindicators

willbeaccepted

andtheseindicators

willbeusedfordecision

makingandplanning

Referencesin

municipalplanningpolicy

documents

andgovernmentdecisionsto

the

sustainabilityindicators

Number

ofdocuments

withreferences

4TA

willstrengthen

thescientificbasisofitsdecision

makingconcerningthemanagem

entofitsUrban

WaterSystem

Thenumber

ofmunicipality

staffthatisusing

resultsfrom

scientificresearchin

theirdailywork

Number

ofstaff

WaterDem

andManagem

ent

5Thetotaldem

andin

TA

forfreshwateristo

be

reducedby10

by2050

Thereductionin

freshwatervolumeim

ported

tothecitycomparedto

the2009value

m3yearor

reduction

6Rainwaterandstorm

waterharvestingfor

non-potable

reuse

inthedomesticsectorwillbe

investigatedandapplied

ifoverallsustainability

ofthesystem

isincreased

Availabilityofastudyonrainwaterandor

storm

waterharvestingin

TA

Availabilityofstudy

Thenumber

ofhouseholdscollectingrainwater

Number

ofhouseholds

Thevolumeofrainwaterandorstorm

water

collectedandusedfornon-potable

use

m3year

7TA

willphase

outtheirrigationofurbanparks

withfreshwaterandwillonly

use

recycled

wastew

ater

forthispurpose

Thevolumeoffreshwaterorrecycled

wastew

aterusedforpark

irrigation

m3year

Percentageoftotalareairrigatedbyfreshwater

8

TA

willinfiltrate

storm

watergeneratedin

itsareainto

theaquiferherebyreducingthespillofwaterto

thesea

reducingthehydraulicloadto

theWWTPand

contributingto

aquifer

replenishmentTA

willtakecare

thatthestorm

waterisnotpolluted

Thepercentageofstorm

waterthatisinfiltrated

into

theaquifer

EnvironmentalProtection

9TA

willrestore

andprotect

itssurface

water

(YarkonRiver)

Thewaterquality

oftheYarkonriver

expressed

incommonly

usedwaterquality

parameters

(BODCOD)

various

10

TA

willminim

izetheenergyconsumptionin

theurban

watersystem

Thetotalquantity

ofenergyfrom

non-renew

able

sources

usedto

operate

theurbanwatersystem

includingwaterheatingin

thehouseholds

kWhyear

Socio-economy

11

TA

willsupply

waterofgoodquality

toitscitizens

atreasonable

price

insufficientqualities

ThefractionofsamplesanalyzedbytheMinistry

ofHealththatdoes

notsatisfythehealthcriteria

Thefrequency

ofsupply

interruptions

Downtimeper

year

12

TA

willensure

equityin

theaccessto

wateraswell

asto

irrigatedgreen

areas

Thespatialdistributionofwaterquality

and

frequency

ofserviceinterruptionsin

thecity

Mapwithwaterquality

andservice

interruptionfrequency

Thegreen

areaavailable

per

personandits

spatialdistribution

Mapwithm

2green

areaper

capita

13

TA

willreduce

therisk

offloodingin

vulnerable

arearsquos

toafrequency

thatisacceptable

toallstakeholderseven

under

future

clim

ate

changescenarios

Thenumber

ofpeople

affectedbyfloodingper

year

Number

ofpeople

per

year

Theeconomic

damagecausedbyflooding

USDyear

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the system The natural precipitation would not besufficient to satisfy current demand therefore largewater imports are required About 7 of the totalsystem inputs infiltrate into the groundwater andare in principle available for recovery from theaquifer In 2008 the municipality pumped slightlymore than 4 MCM from the aquifer therefore theTel Aviv urban area does not directly contribute toaquifer depletion The largest outflow from the city isthe wastewater flow which is treated and reused in theNegev The largest flux that is not beneficially used isthe stormwater flow If all stormwater would becaptured and used for urban purposes then about50 of the urban demand could be met by reclaimedstormwater

34 Results of the energy balance

The water balance for the city was used to calculatethe energy consumption in the urban water system(Figure 8) For each point of energy consumption inthe system the specific energy consumption in kWhm3

was determined as well as the proportion of the totalflow passing through that specific pathway Thus thetotal energy consumption in the system was calculatedas 328 kWhm3 This figure does not include energyconsumption for water heating in the householdThe largest energy consumption in the water systemitself is due to the long distance from the Lake ofGalilee seawater desalination wastewater treatmentand conveyance of effluent to the Negev The current

Table 3 Overview of cluster characteristics

Cluster 1 2 3 4 5 6

Population 80007 49095 84834 14384 91656 74964Total area (ha) 7451 6477 1459 6590 6470 9846Roads ( ha) 1135 976 1579 248 1180 1588Public open space (ha) 1490 648 2927 3927 647 646Unit-blocks (ha) 4825 4854 10084 2415 4643 7612

Table 4 Overview of unit-block characteristics

ClusterNumber ofunit-blocks

Averageoccupancy

Average areaof a unit-block (m2)

Area ofroof m2 (70)

Area ofgarden m2 (15)

Area ofpavement m2 (15)

1 36367 22 1327 929 199 1992 22316 22 2175 1523 326 3263 38561 22 2615 1831 392 3924 6538 22 3694 2586 554 5545 41662 22 1115 780 167 1676 34074 22 2234 1564 335 335

Table 5 Parameters used for the model calibration

Output Calibration parameter Default After calibration Units

Stormwater Percentage area of store 1 22 Pervious storage 1 capacity 32 mmPervious storage 2 capacity 240 mmRoof area maximum initial loss 0 mmEffective roof area 100 Paved area maximum initial loss 0 mmEffective paved area 100 Road area maximum initial loss 0 mmEffective road area 100 Base flow index 055 RatioBase flow recession constant 00025 Ratio

Wastewater Infiltration index 0095 RatioInfiltration store recession constant 012 Ratio of surface runoff as inflow 3 7

Imported water Garden trigger to irrigate 05 062 RatioPublic open space trigger to irrigate 042 062 Ratio

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contribution of desalination is small because only asmall fraction of the water use originates in desalina-tion plants but this is likely to increase in the futureNote that the specific energy consumption for desali-nation is several times the sum of all specific energyconsumption in the rest of the system

Figure 9 compares the energy consumption in TelAviv with some Australian cities (Kenway et al 2008)and with Zaragosa in Spain (SWITCH 2008 unpub-lished data) The energy costs in those cities for watertreatment and water pumping are highly variabledepending on quality and distance of the waterresource The energy consumption for wastewatertreatment and wastewater pumping (not includingconveyance to the Negev) is in the same range asobserved for the other cities

35 Evaluation of strategies ndash for the 2009 populationand average climatic conditions of 1994ndash2007

A Stormwater use and temporary aquifer storage

The number of days with rain in Tel Aviv is on average45 per year but only 31 days have more than 2 mm perday and therefore only a small number of days

Figure 5 Simulated volume of imported water and figures provided by the municipality from 2003 to 2007 (X-axis mmyy)

Figure 6 Total monthly wastewater production of Tel Aviv in year 2008 as estimated based on total Tel Avivrsquos share of totalDan Region wastewater production (lsquoEstimated datarsquo) and as simulated by AquaCycle

Figure 7 Tel Avivrsquos average water balance for 2003ndash2007(Stormwater flux includes the groundwater baseflow)

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generate significant runoff for stormwater harvestingAnother limiting factor in Tel Aviv is that the demandfor stormwater for irrigation is in the dry season whenthere is obviously no stormwater generation Still withthe cluster storage volumes indicated earlier (in total60000 m3 or 033 m3 per household) a reduction inwater import of 34 can be achieved Increasing totalstorage volume increases the percentage water savingbut reduces the efficiency of the tank (Figure 10) Aneconomic analysis is required to determine a feasiblevolume for the cluster stormwater tanks and this inturn determines the potential for water saving ofthis strategy Saving more than 5 by stormwaterharvesting is estimated to be very unlikely

B Rainwater harvesting

This strategy is more effective than strategy A in termsof overall water savings in the city and also moreefficient in terms of the volume of water saved per unit

rainwater tank volume (Figure 10) This difference iscaused by the higher quality of the rainwater whichallows (in this study) use for all household purposesFor a tank of 330 L per household the collectedrainwater is used for 32 and spilled from the tank for68 In strategy A the quality of the stormwater onlyallows use for toilet flushing and it is therefore mostlyspilled from the storage tanks during storm events (peryear 8 usage 92 spillage for the case with 033 m3

tank volume per household) In addition stormwaterin strategy A is in fact hardly used for irrigation sincethe storm events take place outside the irrigationseason Assuming that it is economical feasible toinstall a rainwater tank volume of about 075 m3 perhousehold then a total saving of 10 of water importsinto the city is possible Rozos et al (forthcoming)calculated that a 10 reduction of potable waterdemand in households in a Mediterranean climatewould increase the capital cost of the water supplysystem with about 40 while a 20 reduction in

Figure 8 The energy consuming components of Tel Avivrsquos water system

Figure 9 Energy use intensity of water and wastewater services by city (For Tel Aviv without energy consumption for theconveyance of effluent to irrigation areas in the Negev)Source Kenway et al (2008) SWITCH unpublished data

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demand would be achievable when accepting a 160cost increase (ie even larger storage tanks)

C Permeable pavement

The surface of Tel Aviv is for 30 permeable and 70impermeable according to the calculated and esti-mated physical characteristics of the city (Tables 3and 4) The impermeable surface consists for 33 ofroads and pavements which could be made permeableby application of permeable types of pavementsAssuming that 80 of the roads and pavements canbe made permeable then the total impermeablesurface has been reduced by 26 Simulation withthe model showed that this would result in a reductionin stormwater generation of 20 (from 177 to 141MCM per year) The reduction in stormwater genera-tion is not only due to increased infiltration becausethe model simulates infiltration to increase onlyfrom 23 to 38 MCM per year The rest of thestormwater evaporates from the soil moisture storeand overflows via pervious surface runoff into thedrainage system

The purpose of this strategy would be to increaseaquifer recharge to allow more aquifer abstractionThe extra volume of abstraction per m2 of made-permeable pavement is about 02 m3m2 per yearA financial analysis will most likely show thatthis strategy is not feasible from a financial pointof view

D Wastewater reuse at unit-block scale

The model simulated grey wastewater treatmentstorage and reuse at household scale The storage

tank volumes based on the AquaCycle optimisationroutine resulted in a 21 reduced demand forimported water (99 MCM ) and a 27 reduction inwastewater flows from the city (94 MCM) Spillagefrom the tanks was small and therefore doubling thetank volumes changed the savings to 23 and 29 onlyrespectively Benefits of this strategy are reduced totaldemand which reduces the need for seawater desalina-tion and cost savings for wastewater collection andtreatment Costs of this strategy include costs forthe household-scale treatment and reuse system andthe reduction in effluent availability for agriculturein the Negev Potential health risks from wastewaterstorage and treatment at household and from potentialcross connections in double distribution networksshould also be addressed

E Wastewater reuse at cluster scale

The model simulated grey wastewater treatment andstorage at cluster level and reuse for toilet flushingirrigation of gardens and irrigation of open publicspace The storage tank volumes based on theAquaCycle optimisation routine resulted in a 25reduced demand for imported water (115 MCM )and a 31 reduction in wastewater flows from thecity (108 MCM) Doubling the tank volumeschanged the savings to 32 and 40 respectivelyThe saving of imported water per unit volumestorage tank for the smaller (021 m3household)and larger (042 m3 per household) tanks were 300and 194 m3m3 per year respectively Comparingthese figures to stormwater strategies A and B(Figure 10) clearly shows that wastewater reuse hasmore potential to save imported water and requires

Figure 10 Potential for yearly water saving by implementation of strategies A and B (for the 2009 population and averageclimatic conditions of 1994ndash2007)

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smaller tanks Reason for this difference is thatwastewater supply to the storage tanks is much lessfluctuating than stormwater flows

36 Evaluation of strategies under scenarios till2050 ndash demand for imported water (Indicator 5)

The demand for imported water in the city under thebaseline scenario increases from 472 MCM in 2009 to759 MCM in 2050 (Figure 11) due to populationgrowth The other scenarios slightly increase thedemand for imported water (778 MCM in 2050 forthe extreme scenario) The effect of climate change issmaller than one would maybe expect because thereduction in rainfall in the wet season does not increasethe demand for irrigation water since that demand isthere only in the dry season The increase intemperature during the dry season increases the

evapotranspiration and demand for irrigation waterbut only to a limited extend

The volume of water saved by the differentstrategies is constant with time for the lsquobaselinersquo andlsquono major changersquo scenarios but is affected by thechange in precipitation and temperature in the otherscenarios The volume of water saved by the strategy B(rainwater harvesting) will be less under the latterscenarios because the rainfall is less Figure 11 alsoshows that the volume of water saved in that strategyfluctuates from year to year with the fluctuations inyearly rainfall

The timing of the implementation of the strategiescould be based on keeping the total demand forimported water under a certain level Figure 12 showshow implementation of strategies B and D partlycancels the increase in demand due to populationgrowth

Figure 12 The simulated import of fresh water into Tel Aviv until 2050 based on phased implementation of strategies B and Dunder lsquonormalrsquo and lsquoextremersquo scenarios

Figure 11 The simulated import of fresh water into Tel Aviv until 2050 based on the lsquonormalrsquo scenario and different strategiesEmpirical data for 1996ndash2006 is also shown (source TahalMunicipality of Tel Aviv)

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37 Evaluation of strategies under scenarios till2050 ndash other indicators

Energy consumption per volume of water consumedcould be reduced by various measures such asreduction of physical leakage (Colombo et al 2002)or by optimising pump technology and pumpingschedules Energy consumption of the alternativestrategies was calculated to investigate their effecton the nexus water ndash energy The energy consumptionin the whole urban water system (Table 6) per m3

of water used (imported thorn reused water) in the citywas on average 289 kWh per m3 for the period2009ndash2050 (baseline scenario) Implementation of thestrategies affected the energy consumption in differentways Strategy B with a 330-L tank per householdresults in 274 kWhm3 mainly because rainwatersystems are estimated to use 0278 KWhm3 (Kenwayet al 2008) which is less energy intensive thenimporting water Wastewater treatment and reuse atcluster scale (strategy E 210-L tank per household)reduces energy consumption to 245 kWhm3 but thesame strategy at household (strategy D 200-L tankper household in cluster 1 2 3 5 6 and 100 L incluster 4) scale increases energy consumption till 318kWhm3 This is due to the higher energy con-sumption for on-site wastewater treatment systems(4 kWhm3 Steendam 2009) than for small waste-water treatment plants (estimated as 08 kWhm3

based on a reported range of 039 to 117 kWhm3 by

Young and Koopman 1991) Therefore it seems thatstrategy D performs best for both saving water andsaving energy

Implementation of the strategies will clearly affectsome of the indicators (Table 2 indicators 5 6 7 810) while other indicators are conditions for successfulimplementation (indicators 1 2 4 6) rather thanresults and yet other indicators are not likely to beaffected (indicators 11 12 13) The effect of thestrategies on groundwater quality and receiving surfacewater quality (indicator 9) is unsure and the topic ofongoing investigations

4 Conclusions

Based on the investigation of Tel Avivrsquos urban watersystem and the simulation results of AquaCyclefollowing conclusions are drawn

The volume of water imported into the city (onaverage 47 MCM per year) and the seasonalfluctuations in the period 2003ndash2007 was accu-rately described by the AquaCycle model usingthe input files on climate physical characteristicsof the city surface and average figures fordomestic end-use categories

Evaluation of several strategies to improve thesustainability of the water system showedthat rainwater harvesting from roofs for non-

Table 6 Energy consumption inventory of Tel Avivrsquos water system

Energy consumption(KWhm3)

Proportion oftotal amount

of water Source of data

Pumping water from the Lake ofGalilee to the city

13 90 Mekorot Company

Treating water from the Lake of Galilee 0 100 Mekorot Company(negligible since supplied toconsumer without treatment)

Treating amp pumping Sea water 39 2 Mekorot CompanyPumping groundwater from local wells 0371 8 Tel Aviv MunicipalityTreating groundwater from local wells 0 8 Tel Aviv Municipality

(negligible since supplied toconsumer without treatment)

Pumping for distributing water ndash North area 0103 135 Tel Aviv MunicipalityPumping for distributing water ndash South area 0077 72 Tel Aviv MunicipalityHeating water at household 407 27 EstimationWastewater collection 0111 100 Tel Aviv MunicipalityWastewater treatment 0425 100 Mekorot CompanyPumping treated wastewater for irrigation 145 100 Mekorot CompanyPumping stormwater 0 100 Tel Aviv Municipality

(negligible since dischargeddirectly to the Sea by gravity)

Total ( including heating water at household) 1427Total (not including household heating water ) 328

It was assumed that all water supplied by Mekorot to the city was taken from the Lake of Galilee rather than from groundwater pumpingstations closer to the city (such as Rosh HaAyin)

Based on 1 m3 supplied collected treated and reused

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potable reuse in households is more promisingthan stormwater collection and reuse at clusterscale Assuming that it is feasible to install arainwater tank volume of about 075 m3 perhousehold then a total saving of 10 of waterimports into the city is possible

The overall water mass balance for the cityshowed that this rainwater harvesting strategywould reduce the amount of stormwater thatleaves the city per year from 22 MCM toabout 17 MCM which shows that othertechnologies or approaches are necessary ifone would like to make full beneficial use ofthis resource

Increasing rainwater infiltration for aquiferrecharge is most likely not financially sustainablesince the extra volume of recharge to allow moreaquifer abstraction is only 02 m3year per m2 ofmade-permeable pavement

The largest saving of water imports could beachieved by wastewater reuse for urban non-potable uses Wastewater collection storage(042 m3 per household) treatment and reuse atcluster scale is simulated to result in a 32 and40 reduction in water imports and wastewaterflows respectively

The most important factor of future scenariosfor water demand is population growth Effectsof climate change (reduced rainfall to a max-imum of 30 and increase in temperature to amaximum of 258C) on imported water weremuch smaller not more than 25 increase inthe extreme scenario This is in agreement withRozos et al (forthcoming) who have estimatedfor a Mediterranean climate an increase between0 and 4 depending on the capacity of therainwater harvesting scheme

Energy consumption in the urban water systemwas calculated as 289 kWh per m3 of volume ofwater used (import thorn reuse) in the city forthe period 2009ndash2050 Implementation of thestrategies affects the energy consumption indifferent ways Rainwater harvesting has somepotential to reduce energy consumption (to 274kWh per m3) but the best strategy in thisrespect is wastewater treatment and reuse atcluster scale (245 kWh per m3) The samestrategy at household scale causes an increasein energy consumption (318 kWh per m3)

The results of the model and the scenarioplanning study can be used to score a numberof the suggested sustainability indicators for theurban water system of Tel Aviv and as such canbe used by the multidisciplinary Water Club tosteer the city towards sustainability

Acknowledgements

The authors would like to thank the Dutch governmentfor its support through the NPT programme andthe European Commission for its support through theSWITCH project (FP6 Global Change and Ecosystems018530)

References

Butterworth JA Sutherland A Manning N Darteh BDziegielewska-Geitz M Eckart J Batchelor CMoriarty P Schouten T Da Silva C Verhagen Jand Bury PJ 2008 Building more effective partnershipsfor innovation in urban water management In Interna-tional Conference on Water and Urban DevelopmentParadigms Towards an integration of engineering designand management approaches 15ndash19 September 2008Katholieke Universiteit Leuven Belgium

Cities Alliance 2006 Guide to City Development StrategiesImproving urban performance Washington DC USApp 92

Colombo AF and Karney BW 2002 Energy and costs ofleaky pipes Toward comprehensive picture ASCEJournal of Water Resources Planning and Management128 (6) 441ndash450

ECAampD (European Climate Assessment amp Dataset Project)2008 Data records httpecaknminl [AccessedApril 2010]

Israel Ministry of Environmental Protection 2008 Israelrsquosadaption to climate change ndash Impacts and recommenda-tion httpwwwsvivagovil [Accessed April 2010]

Karka P Manoli E Lekkas DF and AssimacopoulosD 2007 A case study on integrated urban watermodelling using aquacyle In Proceedings of the 10thInternational Conference on Environmental Science ampTechnology Kos Island Greece 5ndash7 September 2007

Kenway SJ Priestley A Cook S Seo S Inman MGregory A and Hall M 2008 Energy use in theprovision and consumption of urban water in Australiaamp New Zealand Water for a Healthy country Flagshipreport series ISSN 1835ndash095X Water Service Associa-tion of Australia

Lundin M 2003 Indicators for measuring the sustainabilityof urban water system ndash A life cycle approach PhDdissertation Chalmers University of Technology

Makropoulos CK Memon FA Shirley-Smith C andButler D 2008a Futures An exploration of scenariosfor sustainable urban water management Water Policy10 345ndash373

Makropoulos CK Natsis K Liu S Mittas K andButler D 2008b Decision support for sustainableoption selection in integrated urban water managementEnvironmental Modelling amp Software 23 (12) 1448ndash1460

Mitchell V 2005 AquaCycle user guide A daily urban waterbalance model Australia Monash University Press

Mitchell V 2006 Applying integrated urban water manage-ment concepts A review of Australian experienceEnvironmental Management 37 (5) 589ndash605

Mitchell V Mein RG and McMahon TA 2001Modelling the urban water cycle Environmental Model-ling amp Software 16 615ndash629

Municipality of Tel Aviv 2006 City ndash The Strategic plan forTel Aviv Yafo Strategic Planning Unit Tel AvivMunicipality Israel

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The drinking water is supplied to the city mainly bythe national water company Mekorot (41 million cubicmetre per year MCMY or 90 of the total supply)through the National Water Carrier (NWC) TheNWC is an integrated national distribution networkthat is fed from the Lake of Galilee (150 km from thecity) several aquifers and recently constructed desali-nation plants Another 10 (around 5 MCMY) issupplied from local wells by the municipality Themunicipality also maintains the pipe-lines and thewater reservoirs in the city and cares for the properwater pressures and disinfection The municipality alsooperates a separate sewer system (around 501 km ofpipes) and pumps the sewage to the WWTP (WasteWater Treatment Plant) through a central collector(Reading-Rishon) both owned by the Dan RegionAssociation of Towns (of which Tel Aviv is a member)Stormwater is collected by gravity and dischargeddirectly without treatment to the Mediterranean SeaMonitoring of and billing for water consumption isalso performed by the municipality

The Dan Region Association of Towns collects andtreats the wastewater from Tel Aviv and surroundingtowns and was established by seven municipalities (TelAviv was the major one) in the 1950s Today there are24 municipalities connected to the central WWTP andaround two million person equivalents of wastewaterare treated The treated water is transferred to theNegev desert for irrigation purposes The duties of theAssociation include the monitoring of the sources ofwastewater A specialised department visits industrialplants and other major wastewater producers in TelAviv and its surroundings to prevent pollution atsource

The major water-related pressure in Tel Aviv ispotential water scarcity as Tel Aviv is one of the largerwater consumers in an arid country that is sufferingfrom water scarcity at the country level Additionalpressures on the city such as population growthurbanisation pollution of aquifers and rise in tem-perature due to climate change may worsen thisproblem These pressures also show that the urbanwater system of Tel Aviv is not fully sustainable

13 Sustainable cities sustainable water systems

One may raise the question when are urban watersystems sustainable Or what kind of changes incurrent urban water systems are required Answeringsuch questions is strategic in order to transform citiesinto long term viable places The main objective of asustainable urban water system is to satisfy thewater related needs of the community at the lowestcost to society while minimising environmental andsocial impact (White and Turner 2003) Thus the

sustainability of the urban water system involveseconomic viability social stability and wise use ofresources and should be considered as a manner toprotect and nourish the natural environment

In order to re-orientate urban areas towardssustainability it is recognised that the different aspectsof urban water systems should be viewed in relationto each other which requires the adoption of anintegrated approach to urban water system planningservice provision and management Integrated urbanwater management takes a comprehensive approach tourban water services viewing water supply drainageand sanitation as components of an integrated physicalsystem and recognises that the physical system sitswithin an organisational framework and a broadernatural landscape (Mitchell 2006)

14 Sustainability indicators and strategic planning

To change cities towards sustainability a changeprocess is required Strategic planning is a tool thatcan be used to direct the overall development of a cityto address challenges and to benefit from opportunities(Cities Alliance 2006) The monitoring of the state of acity (an essential element of the strategic planningcycle) could be based on sustainability indicatorsSustainability indicators are pieces of informationwhich summarise important properties visualise phe-nomenons of interest quantify trends and commu-nicate them to relevant target groups (Lundin 2003)Indicators are a tool for sustainability assessment andconstruction of indicators is a major topic in sustain-ability studies (Scheller 2000)

15 Use of modelling for strategic planning

Sustainability indicators can be used for reportingbut also to evaluate different management options forthe future In this context integrated urban watersystem models can be powerful tools in exploringthe performance (in terms of indicator scores) ofalternative options such as reusendashrecycling schemes(Rozos et al forthcoming) decentralised solutions(Makropoulos et al 2008b) water demand manage-ment schemes etc A model that is taking a whole-of-system perspective is AquaCycle a model that isable to describe and predict the total quantity ofwater moving through the urban water cycle (Mitchellet al 2001) It was developed to provide a holistic viewof an urban water system allowing water supply waterdisposal and storm water to be considered ascomponents within a single framework (Mitchell2005 Karka et al 2007) Based on the AquaCycleoutcomes a number of sustainability indicators can becalculated as will be shown in this research

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The main aim of this research is to develop urbanwater management strategies by applying the Aqua-Cycle model for the investigation of their effects on thesustainability of the water system of Tel Aviv Thesustainability is measured (among others) by indicatorswhich are related to the reduction of freshwaterconsumption energy use and the increase in theamount of wastewater reuse The research is aimed atproviding valuable information for decision makers inTel Aviv to steer the city towards sustainability in asituation of water scarcity

2 Methodology

21 Integration of strategic planning and modelsupported decision making

The methodology is a combination of strategicplanning as described in the Cities Alliance Guide toCity Development Strategies (Cities Alliance 2006) andthe application of a total urban water cycle model Themodel is used to assess the current situation as well asto evaluate future scenarios and strategies (Van derSteen and Howe 2009) The process is an integration ofengineering calculations and a stakeholder involve-ment process As a first step in the process amultistakeholder platform was established which wasnamed the Learning Alliance (or lsquoWater Clubrsquo) ALearning Alliance is an (informal) group of stake-holders that in Tel Aviv jointly (1) Assesses thecurrent shape of the urban water system and for-mulates un-sustainability factors (2) Develops a visionfor the future state of the urban water system (3)Translates the vision in a set of sustainability objectivesand indicators (4) Identifies possible future scenarioswhere scenarios are defined as possible futures that areout of the control by urban water managers such asclimate change (5) Formulates strategies aimed atachieving the vision and (6) Recommends an im-plementation plan to relevant planning authorities (seeFigure 1) (Butterworth et al 2008) The LA workshopswere complemented by collection of secondary datasite visits and by interviewing water sector profes-sionals on their views on the vision scenarios andstrategies The gathered data was used to prepare theinput files for AquaCycle to make a water balance Inaddition was calculated how much energy is requiredfor the various strategies (Figure 2)

22 AquaCycle

AquaCycle is a total urban water cycle modeldeveloped to take a more holistic view allowing watersupply wastewater disposal and storm water drainageto be considered as components within a single systemThe lsquocyclersquo starts with water entering as precipitation

or as (fresh) water imported in order to meet theindoor and outdoor water use requirement The waterthen passes through the households or other waterusers and exits in the form of evapotranspirationstorm water or wastewater (Mitchell 2005) AquaCycleoperates on three different scales (unit-block clusterand catchment) (see Figure 3) in order to enable thesimulation of any urban form The input data for themodel which uses a time step of one day includesclimate data indoor water use data and site character-istics Surfaces are divided into two categoriespervious and impervious Impervious surfaces includeroofs roads and pavement Pervious areas are house-hold gardens and open public space (parks) and aremodelled as single stores that overflow when full intothe drainage system Water evaporation from bothpervious and impervious areas is calculated accordingto daily potential evapotranspiration values Theamount of water imported into an area is the sum ofindoor water use irrigation and leakage The totalwastewater discharge from the catchment is the sum ofindoor water use infiltration and inflow from thestorm water drainage system (Mitchell 2005)

The application of AquaCycle to Tel Avivrsquos watersystem involved the determination of three groups of

Figure 1 Overview of (on-going) strategic planning exercisefor the water system of Tel Aviv

Figure 2 Procedures of research methodology (numberindicates order of the steps in the process)

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data meteorological data indoor water use profile andphysical site characteristics The details about datacollection and processing are presented below

23 Meteorological data

The climate data input file is a series of dailyprecipitation and potential evaporation figures from1994 to 2007 Precipitation data of Tel Aviv wasobtained directly from the European Climate Assess-ment amp Data set project (ECAampD 2008) Potentialevaporation data was estimated based on monthlyheat indexes and the equations presented by theThornthwaite method (Thornthwaite 1948) The timeseries was used to simulate future precipitation Forthe baseline scenario the time series was assumed torepeat itself in 2009ndash2022 2023ndash2036 etc For thelsquonormal scenariorsquo the time series was used without anyadjustments from 2009 to 2022 while precipitation wasreduced by 10 for the period 2023ndash2050 andtemperature was increased by 158C for the sameperiod For the lsquoextremersquo scenario the values were 15and 258C respectively The lsquonormalrsquo scenario is basedon the climate change estimation of the Israel Ministryof Environmental Protection (2008) The lsquoextremersquoscenario was included to investigate the response of theurban water system to more extreme climate change

24 Indoor water use profile

Average yearly household water consumption figureswere obtained from the municipality as well asconsumption figures for public buildings health carehotels businesses sport facilities security transportand construction Since AquaCycle only considerslsquohouseholdsrsquo as water consumers (apart from publicirrigation) it was assumed that households areconsuming the sum of the consumption in the sectorsmentioned above These figures include the consump-tion by the day-time residents The consumption per

household was calculated by dividing that sum bythe number of households The end-use of water inhouseholds (in kitchen bathroom garden etc) is notknown for Tel Aviv and therefore the indoor waterusage profile for kitchen bathroom laundry and toiletof Canberra (Mitchell 2005) was copied and adjustedpro rata to a total household consumption ascalculated for Tel Aviv

25 Physical site characteristics

The municipal boundaries of the city were taken as thecatchment boundary The catchment was divided intosix clusters These six clusters were formed by groupingthe 37 sub-catchments of the drainage system suchthat each group of sub-catchments equalled (as muchas possible) one of the city-quarters used by theStatistics department of the municipality Informationof total area population and land use by quarter (nownamed cluster) was available from the StatisticsDepartment and was used as input data for AquaCycle(Figure 4) The road area and the open space area ineach cluster were estimated based on satellite imagesmaps of land use and detailed information from theStrategic Planning Unit of Tel Aviv Municipality(Municipality of Tel Aviv 2006)

Though the study area includes residential com-mercial and public buildings it was assumed that allbuildings are residential buildings This assumption isin line with the previous assumption on the allocationof all water consumption (except public irrigation) tohouseholds Since most of the buildings in Tel Aviv areapartment blocks the assumption seems reasonableThe typical apartment block houses several householdunits (apartments) and one apartment is equal to oneunit-block in the model The number of unit-blocks ineach cluster was calculated by dividing the totalpopulation of a cluster by the average number ofoccupants per household (22 Statistics Department)The total area of unit-blocks in each cluster was

Figure 3 Spatial scales used in AquaCycle The area of garden roof and pavement in the unit-block in the model is asmeasured for the typical multi-unit apartment block but divided by the number of apartments in the block

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calculated based on the total area of a cluster minusthe area of roads and public open spaces The averagearea of one unit-block was obtained from the total areaof unit-blocks and the number of unit-blocks withinthe cluster Physical characteristics of a representativeapartment block were estimated by observation basedon satellite images and site visits It was estimated thatthe areas of roof garden and pavement per apartmentblock are 70 15 and 15 respectively The areas wereproportionally allocated to the apartments in the blockand therefore the percentages are also valid for theunit-blocks in the model

26 AquaCycle outputs and energy calculations

The output of the model is a water balance with dailyvalues for precipitation piped water supply evapo-transpiration stormwater drainage and wastewatercollection Monthly or yearly average values can becalculated for the catchment cluster or unit-blockscale The mass balance for the catchment scale wasused to calculate the total energy consumption of thesystem All components of the water system thatconsume energy were identified by interviewing staff ofTel Aviv municipality and the Mekorot company anddata on energy consumption (mostly in kWhm3) wereobtained

27 Formulation of scenarios

Scenarios were not formulated to predict the futurebut were used by the LA as tools for thinking about

possible futures and to evaluate the impact ofdecisions taken today on these futures Commonelements in the scenarios were based on regulatorysocial economic environmental and technical aspects(Makropoulos et al 2008a) but not all of theseelements can be modelled quantitatively In thiswork four quantitative scenarios were formulatedfor Tel Aviv until the year 2050 including fourfactors precipitation temperature population growthand urbanisation all of which can be simulated byAquaCycle simulation (see Table 1) All of thesefactors impact directly or indirectly on Tel Avivrsquosurban water system via the effects on water demandwater resources water infrastructure and urban sur-face permeability The baseline scenario describes thecurrent situation of the city The lsquonormalrsquo scenario isbased on estimations on climate change by IsraelMinistry of Environmental Protection (2008) Data onhistorical population growth rate (22) was obtainedfrom Tel Aviv Municipality The scenarios assumedthe same growth rate to continue until 2050 whichwould only be possible by densification and morehigh-rise buildings in the city In all scenariosdensification leads to a reduction in (permeable) publicopen space of 20

28 Formulation of strategies

The LA developed strategies to achieve the visiongiven the possible future scenarios through groupdiscussions and by one-on-one interviews Onlystrategies that could be simulated by AquaCycle arepresented here The strategies are

A Stormwater use and temporary aquifer storage

Measures for stormwater use and aquifer infiltrationprojects were simulated for each cluster The storm-water from the unit-blocks and from the roads drainedinto a stormwater storage tank in each cluster and wasreused for toilet flushing garden and public spaceirrigation Excess stormwater was infiltrated into theaquifer The stormwater surface storage volumesinitially used were cluster 1 15000 m3 cluster 25000 m3 cluster 3 15000 m3 cluster 4 15000 m3cluster 5 5000 m3 cluster 6 5000 m3 (based on theoptimisation routine of AquaCycle) A 10000 m3 ofaquifer storage was applied for each cluster The effectof increasing and decreasing these volumes wasinvestigated as well

B Rainwater harvesting

A rainwater tank of various sizes was applied atevery household in all clusters of the city Rain

Figure 4 Clusters defined for the Tel Aviv catchment(Numbers 1ndash6) and Tel Avivrsquos neighbouring municipalities

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water was used in the kitchen for laundry inthe bathroom for toilet flushing and for gardenirrigation

C Permeable pavement

Pavements in unit-block gardens and for roads werereplaced by permeable pavements simulated in Aqua-Cycle by increasing the garden and open space area inthe city

D Wastewater reuse at unit-block scale

Decentralised wastewater treatment units were appliedat every household in the city Wastewater fromkitchen bathroom and laundry was treated and reusedfor toilet flushing and garden irrigation It wasassumed that no water was lost in the treatmentprocess The storage volume for treated wastewater atevery household in each cluster was identified accord-ing to the optimisation results of AquaCycle (200 L ofwastewater storage per household in cluster 1 2 3 56 and 100 L of wastewater storage in cluster 4)

E Wastewater reuse at cluster scale

Wastewater treatment units were applied for eachcluster Household wastewater draining to a clusterwastewater storage tank was treated stored andsupplied for toilet flushing and garden irrigation forhouseholds and for open space irrigation It wasassumed that no water was lost in the treatmentprocess The treated wastewater storage volumes werecluster 1 7900 m3 cluster 2 4700 m3 cluster 38300 m3 cluster 4 1300 m3 cluster 5 9100 m3cluster 6 7200 m3 (based on the optimisation routineof AquaCycle)

29 Evaluation of strategies

As mentioned above the LA developed a vision for asustainable urban water system for the city This visionwas translated into tangible objectives the achieve-ment of which can be measured by sustainabilityindicators The score for these indicators were used toevaluate the strategies rather than by a thoroughengineering and economic feasibility study Some ofthe indicators could be evaluated in a quantitative wayusing the AquaCycle outputs others were evaluatedqualitatively

3 Results and discussion

31 Sustainability objectives and indicators

Based on interviews and general investigations it wasfound that the urban water system of Tel Aviv istypical for an advanced developed country but alsocharacterised by a number of un-sustainability factorswhich need improvement With regard to planning ofthe whole system it was noticed that lsquowater manage-mentrsquo is not addressed in the Strategic Plan of the city(Municipality of Tel Aviv 2006) and water indicatorsare therefore also not included in the set of indicatorsthat is used to monitor the development of the cityThis is somewhat surprising since the domestic waterconsumption in the city is higher than the amount thatcan be sustained from renewable water sources Thewater supply system is also threatened by insufficientmaintenance of the distribution system which causesbio-film growth and microbial pollution which in turnmay cause a higher chlorine demand One of theunderlying causes of the poor maintenance is lack ofsuitable financial resources for local government tomaintain the drinking water quality The same reasonsalso result in frequent leakages from the sewer system

Table 1 Formulated scenarios and factors until the year 2050

FactorPrecipitationdecrease

Temperatureincrease

Populationgrowth rate Urbanisation

Baseline scenario ndash ndash 22lsquoNo major changersquo scenario ndash ndash 22 20 of public open space is replaced

by residential area (10 in 2022 andanother 10 in 2046) road area isnot changed

lsquoNormalrsquo scenario 20 158C 22 20 of public open space is replacedby residential area (10 in 2022 andanother 10 in 2046) road area isnot changed

lsquoExtremersquo scenario 30 258C 22 20 of public open space is replacedby residential area (10 in 2022 andanother 10 in 2046) road area isnot changed

From 2023 onwards

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which causes severe pollution of the local aquiferwhich is one of the drinking water sources for the cityBasically all municipal wastewater is collected andtreated to a tertiary level but it is not utilised foragricultural irrigation within the region but in theNegev Urban parks in Tel Aviv are still irrigated withfresh water Stormwater is collected in a separatedrainage system but discharged directly to the seawithout any treatment There is no monitoring systemor research to evaluate the amount of stormwatergenerated in the city and its quality It is likely that TelAviv is overlooking the potential to use this nonconventional water resource The capacity of thedrainage system is not sufficient to prevent occasionalflooding Finally the un-sustainability of the systembecomes clear from the significant amount of energyused to transport fresh water over long distances anduphill (from the Sea of Galilee) to treat wastewater inan energy intensive system and finally to pump effluentto irrigation fields in the south of the country Thecommissioning of desalination plants will only increasethe energy consumption in the system

Based on this assessment the LA formulated aVision for sustainable urban water management in TelAviv lsquoTel Avivrsquos water system management will beestablished based on sustainability indicators andapply an efficient and integrated water managementto meet the water demand of citizens and for otherapplications with sufficient qualities and reasonableprices while the natural status of water resources isassuredrsquo The vision was translated into a set oftangible objectives and related indicators as shownin Table 2

32 Model calibration and simulation of wastewateroutput

The characteristics of the modelled clusters and therepresentative unit-block are outlined in Table 3 and 4The meteorological data the indoor water use profileand physical site characteristics were used as inputsfor the model The default calibration parameters(Table 5) initially were used and the model output interms of lsquoimported waterrsquo was compared with themunicipalities measured data on total water distrib-uted to the consumers The average amount oflsquoimported waterrsquo simulated by the model was about10 lower than the total water consumption Thelsquotrigger to irrigatersquo is the fraction of the optimal soilmoisture for plant growth which is still acceptable tothe user This trigger for private gardens and publicopen space was adjusted to 062 and as a result theaverage lsquoimported waterrsquo simulated by the model thenwas exactly the average volume of water distributed tothe consumers (Figure 5)

The monthly water consumption in the city isabout 40 higher in the summer irrigation seasonthan in the winter season The seasonal fluctuationcould be described well by the model throughirrigation of private gardens and public open spaceIt is likely that also the indoor water use is higher insummer but it is not possible in AquaCycle to changethe household indoor water consumption between theseasons Variation in imported water based on thefigures provided by the municipality (Figure 5) isrelatively large between some of the summer monthsespecially in 2004 and 2007 The reason for these largerfluctuations is unknown since the differences intemperature and potential evapotranspiration do notseem to explain such large fluctuations The model istherefore also not able to describe well these short-termfluctuations

Further calibration of the model was attemptedon observed wastewater flows from the wider TelAviv area (the Dan District) Unfortunately thewastewater flow from Tel Aviv is not measuredseparately from the wastewater flow from surround-ing municipalities It was therefore assumed that theamount of wastewater production per capita per yearin the various municipalities in the Dan District is thesame Therefore based on the population of TelAviv the amount of wastewater generated from TelAviv is estimated as 326 of total wastewaterproduction of the Dan District The wastewater flowssimulated by AquaCycle in the dry season (AprilndashOctober) were 18 lower than the flows based onmeasurements and the above described calculation(Figure 6) The simulated values may actually becloser to reality since the simulated values are90 of the indoor water consumption (about 31MCMmonth Figure 5) whereas the measured value(adjusted for population) is more than the actualindoor water consumption The higher flows inJanuary March and December are caused by wrongconnections between the stormwater drainage andfoul sewerage system The observed increase due tostormwater infiltration could be used to adjust thecalibration parameter lsquo of surface runoff as inflowrsquo(Table 5) The default value is 3 but a better fitwas achieved by using 7 This percentage is similarto the estimate of infiltration by Mekorot theoperator of the treatment plant (Aharoni personalcommunication)

33 The water balance of the system

The calibrated model was used to prepare the averageannual water balance for the city for the years2003ndash2007 (Figure 7) The water balance can be usedfor a fundamental evaluation of the sustainability of

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Table

2

Specificobjectives

andsustainabilityindicators

fortheurbanwatersystem

ofTel

Aviv

Specificobjective

Indicator

Unit

WaterPolicy

1TA

willraiseawarenessamongitscitizensabout

lsquowaterandsustainabilityrsquoandwillinvolvethe

publicin

decisionmaking

Thenumber

ofcitizensthatwillparticipate

inconsultativemeetings

Number

ofcitizensper

year

2TA

willmanageitsurbanwatersystem

inan

integratedwayintegratingaspects

ofwater

supplystorm

wateramp

wastew

atermanagem

ent

Theproductionofanintegratedurbanwater

managem

entplanforthecity

at2-yearintervals

Tim

elyproductionofintegratedplan

3A

setofsustainabilityindicators

willbeaccepted

andtheseindicators

willbeusedfordecision

makingandplanning

Referencesin

municipalplanningpolicy

documents

andgovernmentdecisionsto

the

sustainabilityindicators

Number

ofdocuments

withreferences

4TA

willstrengthen

thescientificbasisofitsdecision

makingconcerningthemanagem

entofitsUrban

WaterSystem

Thenumber

ofmunicipality

staffthatisusing

resultsfrom

scientificresearchin

theirdailywork

Number

ofstaff

WaterDem

andManagem

ent

5Thetotaldem

andin

TA

forfreshwateristo

be

reducedby10

by2050

Thereductionin

freshwatervolumeim

ported

tothecitycomparedto

the2009value

m3yearor

reduction

6Rainwaterandstorm

waterharvestingfor

non-potable

reuse

inthedomesticsectorwillbe

investigatedandapplied

ifoverallsustainability

ofthesystem

isincreased

Availabilityofastudyonrainwaterandor

storm

waterharvestingin

TA

Availabilityofstudy

Thenumber

ofhouseholdscollectingrainwater

Number

ofhouseholds

Thevolumeofrainwaterandorstorm

water

collectedandusedfornon-potable

use

m3year

7TA

willphase

outtheirrigationofurbanparks

withfreshwaterandwillonly

use

recycled

wastew

ater

forthispurpose

Thevolumeoffreshwaterorrecycled

wastew

aterusedforpark

irrigation

m3year

Percentageoftotalareairrigatedbyfreshwater

8

TA

willinfiltrate

storm

watergeneratedin

itsareainto

theaquiferherebyreducingthespillofwaterto

thesea

reducingthehydraulicloadto

theWWTPand

contributingto

aquifer

replenishmentTA

willtakecare

thatthestorm

waterisnotpolluted

Thepercentageofstorm

waterthatisinfiltrated

into

theaquifer

EnvironmentalProtection

9TA

willrestore

andprotect

itssurface

water

(YarkonRiver)

Thewaterquality

oftheYarkonriver

expressed

incommonly

usedwaterquality

parameters

(BODCOD)

various

10

TA

willminim

izetheenergyconsumptionin

theurban

watersystem

Thetotalquantity

ofenergyfrom

non-renew

able

sources

usedto

operate

theurbanwatersystem

includingwaterheatingin

thehouseholds

kWhyear

Socio-economy

11

TA

willsupply

waterofgoodquality

toitscitizens

atreasonable

price

insufficientqualities

ThefractionofsamplesanalyzedbytheMinistry

ofHealththatdoes

notsatisfythehealthcriteria

Thefrequency

ofsupply

interruptions

Downtimeper

year

12

TA

willensure

equityin

theaccessto

wateraswell

asto

irrigatedgreen

areas

Thespatialdistributionofwaterquality

and

frequency

ofserviceinterruptionsin

thecity

Mapwithwaterquality

andservice

interruptionfrequency

Thegreen

areaavailable

per

personandits

spatialdistribution

Mapwithm

2green

areaper

capita

13

TA

willreduce

therisk

offloodingin

vulnerable

arearsquos

toafrequency

thatisacceptable

toallstakeholderseven

under

future

clim

ate

changescenarios

Thenumber

ofpeople

affectedbyfloodingper

year

Number

ofpeople

per

year

Theeconomic

damagecausedbyflooding

USDyear

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the system The natural precipitation would not besufficient to satisfy current demand therefore largewater imports are required About 7 of the totalsystem inputs infiltrate into the groundwater andare in principle available for recovery from theaquifer In 2008 the municipality pumped slightlymore than 4 MCM from the aquifer therefore theTel Aviv urban area does not directly contribute toaquifer depletion The largest outflow from the city isthe wastewater flow which is treated and reused in theNegev The largest flux that is not beneficially used isthe stormwater flow If all stormwater would becaptured and used for urban purposes then about50 of the urban demand could be met by reclaimedstormwater

34 Results of the energy balance

The water balance for the city was used to calculatethe energy consumption in the urban water system(Figure 8) For each point of energy consumption inthe system the specific energy consumption in kWhm3

was determined as well as the proportion of the totalflow passing through that specific pathway Thus thetotal energy consumption in the system was calculatedas 328 kWhm3 This figure does not include energyconsumption for water heating in the householdThe largest energy consumption in the water systemitself is due to the long distance from the Lake ofGalilee seawater desalination wastewater treatmentand conveyance of effluent to the Negev The current

Table 3 Overview of cluster characteristics

Cluster 1 2 3 4 5 6

Population 80007 49095 84834 14384 91656 74964Total area (ha) 7451 6477 1459 6590 6470 9846Roads ( ha) 1135 976 1579 248 1180 1588Public open space (ha) 1490 648 2927 3927 647 646Unit-blocks (ha) 4825 4854 10084 2415 4643 7612

Table 4 Overview of unit-block characteristics

ClusterNumber ofunit-blocks

Averageoccupancy

Average areaof a unit-block (m2)

Area ofroof m2 (70)

Area ofgarden m2 (15)

Area ofpavement m2 (15)

1 36367 22 1327 929 199 1992 22316 22 2175 1523 326 3263 38561 22 2615 1831 392 3924 6538 22 3694 2586 554 5545 41662 22 1115 780 167 1676 34074 22 2234 1564 335 335

Table 5 Parameters used for the model calibration

Output Calibration parameter Default After calibration Units

Stormwater Percentage area of store 1 22 Pervious storage 1 capacity 32 mmPervious storage 2 capacity 240 mmRoof area maximum initial loss 0 mmEffective roof area 100 Paved area maximum initial loss 0 mmEffective paved area 100 Road area maximum initial loss 0 mmEffective road area 100 Base flow index 055 RatioBase flow recession constant 00025 Ratio

Wastewater Infiltration index 0095 RatioInfiltration store recession constant 012 Ratio of surface runoff as inflow 3 7

Imported water Garden trigger to irrigate 05 062 RatioPublic open space trigger to irrigate 042 062 Ratio

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contribution of desalination is small because only asmall fraction of the water use originates in desalina-tion plants but this is likely to increase in the futureNote that the specific energy consumption for desali-nation is several times the sum of all specific energyconsumption in the rest of the system

Figure 9 compares the energy consumption in TelAviv with some Australian cities (Kenway et al 2008)and with Zaragosa in Spain (SWITCH 2008 unpub-lished data) The energy costs in those cities for watertreatment and water pumping are highly variabledepending on quality and distance of the waterresource The energy consumption for wastewatertreatment and wastewater pumping (not includingconveyance to the Negev) is in the same range asobserved for the other cities

35 Evaluation of strategies ndash for the 2009 populationand average climatic conditions of 1994ndash2007

A Stormwater use and temporary aquifer storage

The number of days with rain in Tel Aviv is on average45 per year but only 31 days have more than 2 mm perday and therefore only a small number of days

Figure 5 Simulated volume of imported water and figures provided by the municipality from 2003 to 2007 (X-axis mmyy)

Figure 6 Total monthly wastewater production of Tel Aviv in year 2008 as estimated based on total Tel Avivrsquos share of totalDan Region wastewater production (lsquoEstimated datarsquo) and as simulated by AquaCycle

Figure 7 Tel Avivrsquos average water balance for 2003ndash2007(Stormwater flux includes the groundwater baseflow)

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generate significant runoff for stormwater harvestingAnother limiting factor in Tel Aviv is that the demandfor stormwater for irrigation is in the dry season whenthere is obviously no stormwater generation Still withthe cluster storage volumes indicated earlier (in total60000 m3 or 033 m3 per household) a reduction inwater import of 34 can be achieved Increasing totalstorage volume increases the percentage water savingbut reduces the efficiency of the tank (Figure 10) Aneconomic analysis is required to determine a feasiblevolume for the cluster stormwater tanks and this inturn determines the potential for water saving ofthis strategy Saving more than 5 by stormwaterharvesting is estimated to be very unlikely

B Rainwater harvesting

This strategy is more effective than strategy A in termsof overall water savings in the city and also moreefficient in terms of the volume of water saved per unit

rainwater tank volume (Figure 10) This difference iscaused by the higher quality of the rainwater whichallows (in this study) use for all household purposesFor a tank of 330 L per household the collectedrainwater is used for 32 and spilled from the tank for68 In strategy A the quality of the stormwater onlyallows use for toilet flushing and it is therefore mostlyspilled from the storage tanks during storm events (peryear 8 usage 92 spillage for the case with 033 m3

tank volume per household) In addition stormwaterin strategy A is in fact hardly used for irrigation sincethe storm events take place outside the irrigationseason Assuming that it is economical feasible toinstall a rainwater tank volume of about 075 m3 perhousehold then a total saving of 10 of water importsinto the city is possible Rozos et al (forthcoming)calculated that a 10 reduction of potable waterdemand in households in a Mediterranean climatewould increase the capital cost of the water supplysystem with about 40 while a 20 reduction in

Figure 8 The energy consuming components of Tel Avivrsquos water system

Figure 9 Energy use intensity of water and wastewater services by city (For Tel Aviv without energy consumption for theconveyance of effluent to irrigation areas in the Negev)Source Kenway et al (2008) SWITCH unpublished data

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demand would be achievable when accepting a 160cost increase (ie even larger storage tanks)

C Permeable pavement

The surface of Tel Aviv is for 30 permeable and 70impermeable according to the calculated and esti-mated physical characteristics of the city (Tables 3and 4) The impermeable surface consists for 33 ofroads and pavements which could be made permeableby application of permeable types of pavementsAssuming that 80 of the roads and pavements canbe made permeable then the total impermeablesurface has been reduced by 26 Simulation withthe model showed that this would result in a reductionin stormwater generation of 20 (from 177 to 141MCM per year) The reduction in stormwater genera-tion is not only due to increased infiltration becausethe model simulates infiltration to increase onlyfrom 23 to 38 MCM per year The rest of thestormwater evaporates from the soil moisture storeand overflows via pervious surface runoff into thedrainage system

The purpose of this strategy would be to increaseaquifer recharge to allow more aquifer abstractionThe extra volume of abstraction per m2 of made-permeable pavement is about 02 m3m2 per yearA financial analysis will most likely show thatthis strategy is not feasible from a financial pointof view

D Wastewater reuse at unit-block scale

The model simulated grey wastewater treatmentstorage and reuse at household scale The storage

tank volumes based on the AquaCycle optimisationroutine resulted in a 21 reduced demand forimported water (99 MCM ) and a 27 reduction inwastewater flows from the city (94 MCM) Spillagefrom the tanks was small and therefore doubling thetank volumes changed the savings to 23 and 29 onlyrespectively Benefits of this strategy are reduced totaldemand which reduces the need for seawater desalina-tion and cost savings for wastewater collection andtreatment Costs of this strategy include costs forthe household-scale treatment and reuse system andthe reduction in effluent availability for agriculturein the Negev Potential health risks from wastewaterstorage and treatment at household and from potentialcross connections in double distribution networksshould also be addressed

E Wastewater reuse at cluster scale

The model simulated grey wastewater treatment andstorage at cluster level and reuse for toilet flushingirrigation of gardens and irrigation of open publicspace The storage tank volumes based on theAquaCycle optimisation routine resulted in a 25reduced demand for imported water (115 MCM )and a 31 reduction in wastewater flows from thecity (108 MCM) Doubling the tank volumeschanged the savings to 32 and 40 respectivelyThe saving of imported water per unit volumestorage tank for the smaller (021 m3household)and larger (042 m3 per household) tanks were 300and 194 m3m3 per year respectively Comparingthese figures to stormwater strategies A and B(Figure 10) clearly shows that wastewater reuse hasmore potential to save imported water and requires

Figure 10 Potential for yearly water saving by implementation of strategies A and B (for the 2009 population and averageclimatic conditions of 1994ndash2007)

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smaller tanks Reason for this difference is thatwastewater supply to the storage tanks is much lessfluctuating than stormwater flows

36 Evaluation of strategies under scenarios till2050 ndash demand for imported water (Indicator 5)

The demand for imported water in the city under thebaseline scenario increases from 472 MCM in 2009 to759 MCM in 2050 (Figure 11) due to populationgrowth The other scenarios slightly increase thedemand for imported water (778 MCM in 2050 forthe extreme scenario) The effect of climate change issmaller than one would maybe expect because thereduction in rainfall in the wet season does not increasethe demand for irrigation water since that demand isthere only in the dry season The increase intemperature during the dry season increases the

evapotranspiration and demand for irrigation waterbut only to a limited extend

The volume of water saved by the differentstrategies is constant with time for the lsquobaselinersquo andlsquono major changersquo scenarios but is affected by thechange in precipitation and temperature in the otherscenarios The volume of water saved by the strategy B(rainwater harvesting) will be less under the latterscenarios because the rainfall is less Figure 11 alsoshows that the volume of water saved in that strategyfluctuates from year to year with the fluctuations inyearly rainfall

The timing of the implementation of the strategiescould be based on keeping the total demand forimported water under a certain level Figure 12 showshow implementation of strategies B and D partlycancels the increase in demand due to populationgrowth

Figure 12 The simulated import of fresh water into Tel Aviv until 2050 based on phased implementation of strategies B and Dunder lsquonormalrsquo and lsquoextremersquo scenarios

Figure 11 The simulated import of fresh water into Tel Aviv until 2050 based on the lsquonormalrsquo scenario and different strategiesEmpirical data for 1996ndash2006 is also shown (source TahalMunicipality of Tel Aviv)

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37 Evaluation of strategies under scenarios till2050 ndash other indicators

Energy consumption per volume of water consumedcould be reduced by various measures such asreduction of physical leakage (Colombo et al 2002)or by optimising pump technology and pumpingschedules Energy consumption of the alternativestrategies was calculated to investigate their effecton the nexus water ndash energy The energy consumptionin the whole urban water system (Table 6) per m3

of water used (imported thorn reused water) in the citywas on average 289 kWh per m3 for the period2009ndash2050 (baseline scenario) Implementation of thestrategies affected the energy consumption in differentways Strategy B with a 330-L tank per householdresults in 274 kWhm3 mainly because rainwatersystems are estimated to use 0278 KWhm3 (Kenwayet al 2008) which is less energy intensive thenimporting water Wastewater treatment and reuse atcluster scale (strategy E 210-L tank per household)reduces energy consumption to 245 kWhm3 but thesame strategy at household (strategy D 200-L tankper household in cluster 1 2 3 5 6 and 100 L incluster 4) scale increases energy consumption till 318kWhm3 This is due to the higher energy con-sumption for on-site wastewater treatment systems(4 kWhm3 Steendam 2009) than for small waste-water treatment plants (estimated as 08 kWhm3

based on a reported range of 039 to 117 kWhm3 by

Young and Koopman 1991) Therefore it seems thatstrategy D performs best for both saving water andsaving energy

Implementation of the strategies will clearly affectsome of the indicators (Table 2 indicators 5 6 7 810) while other indicators are conditions for successfulimplementation (indicators 1 2 4 6) rather thanresults and yet other indicators are not likely to beaffected (indicators 11 12 13) The effect of thestrategies on groundwater quality and receiving surfacewater quality (indicator 9) is unsure and the topic ofongoing investigations

4 Conclusions

Based on the investigation of Tel Avivrsquos urban watersystem and the simulation results of AquaCyclefollowing conclusions are drawn

The volume of water imported into the city (onaverage 47 MCM per year) and the seasonalfluctuations in the period 2003ndash2007 was accu-rately described by the AquaCycle model usingthe input files on climate physical characteristicsof the city surface and average figures fordomestic end-use categories

Evaluation of several strategies to improve thesustainability of the water system showedthat rainwater harvesting from roofs for non-

Table 6 Energy consumption inventory of Tel Avivrsquos water system

Energy consumption(KWhm3)

Proportion oftotal amount

of water Source of data

Pumping water from the Lake ofGalilee to the city

13 90 Mekorot Company

Treating water from the Lake of Galilee 0 100 Mekorot Company(negligible since supplied toconsumer without treatment)

Treating amp pumping Sea water 39 2 Mekorot CompanyPumping groundwater from local wells 0371 8 Tel Aviv MunicipalityTreating groundwater from local wells 0 8 Tel Aviv Municipality

(negligible since supplied toconsumer without treatment)

Pumping for distributing water ndash North area 0103 135 Tel Aviv MunicipalityPumping for distributing water ndash South area 0077 72 Tel Aviv MunicipalityHeating water at household 407 27 EstimationWastewater collection 0111 100 Tel Aviv MunicipalityWastewater treatment 0425 100 Mekorot CompanyPumping treated wastewater for irrigation 145 100 Mekorot CompanyPumping stormwater 0 100 Tel Aviv Municipality

(negligible since dischargeddirectly to the Sea by gravity)

Total ( including heating water at household) 1427Total (not including household heating water ) 328

It was assumed that all water supplied by Mekorot to the city was taken from the Lake of Galilee rather than from groundwater pumpingstations closer to the city (such as Rosh HaAyin)

Based on 1 m3 supplied collected treated and reused

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potable reuse in households is more promisingthan stormwater collection and reuse at clusterscale Assuming that it is feasible to install arainwater tank volume of about 075 m3 perhousehold then a total saving of 10 of waterimports into the city is possible

The overall water mass balance for the cityshowed that this rainwater harvesting strategywould reduce the amount of stormwater thatleaves the city per year from 22 MCM toabout 17 MCM which shows that othertechnologies or approaches are necessary ifone would like to make full beneficial use ofthis resource

Increasing rainwater infiltration for aquiferrecharge is most likely not financially sustainablesince the extra volume of recharge to allow moreaquifer abstraction is only 02 m3year per m2 ofmade-permeable pavement

The largest saving of water imports could beachieved by wastewater reuse for urban non-potable uses Wastewater collection storage(042 m3 per household) treatment and reuse atcluster scale is simulated to result in a 32 and40 reduction in water imports and wastewaterflows respectively

The most important factor of future scenariosfor water demand is population growth Effectsof climate change (reduced rainfall to a max-imum of 30 and increase in temperature to amaximum of 258C) on imported water weremuch smaller not more than 25 increase inthe extreme scenario This is in agreement withRozos et al (forthcoming) who have estimatedfor a Mediterranean climate an increase between0 and 4 depending on the capacity of therainwater harvesting scheme

Energy consumption in the urban water systemwas calculated as 289 kWh per m3 of volume ofwater used (import thorn reuse) in the city forthe period 2009ndash2050 Implementation of thestrategies affects the energy consumption indifferent ways Rainwater harvesting has somepotential to reduce energy consumption (to 274kWh per m3) but the best strategy in thisrespect is wastewater treatment and reuse atcluster scale (245 kWh per m3) The samestrategy at household scale causes an increasein energy consumption (318 kWh per m3)

The results of the model and the scenarioplanning study can be used to score a numberof the suggested sustainability indicators for theurban water system of Tel Aviv and as such canbe used by the multidisciplinary Water Club tosteer the city towards sustainability

Acknowledgements

The authors would like to thank the Dutch governmentfor its support through the NPT programme andthe European Commission for its support through theSWITCH project (FP6 Global Change and Ecosystems018530)

References

Butterworth JA Sutherland A Manning N Darteh BDziegielewska-Geitz M Eckart J Batchelor CMoriarty P Schouten T Da Silva C Verhagen Jand Bury PJ 2008 Building more effective partnershipsfor innovation in urban water management In Interna-tional Conference on Water and Urban DevelopmentParadigms Towards an integration of engineering designand management approaches 15ndash19 September 2008Katholieke Universiteit Leuven Belgium

Cities Alliance 2006 Guide to City Development StrategiesImproving urban performance Washington DC USApp 92

Colombo AF and Karney BW 2002 Energy and costs ofleaky pipes Toward comprehensive picture ASCEJournal of Water Resources Planning and Management128 (6) 441ndash450

ECAampD (European Climate Assessment amp Dataset Project)2008 Data records httpecaknminl [AccessedApril 2010]

Israel Ministry of Environmental Protection 2008 Israelrsquosadaption to climate change ndash Impacts and recommenda-tion httpwwwsvivagovil [Accessed April 2010]

Karka P Manoli E Lekkas DF and AssimacopoulosD 2007 A case study on integrated urban watermodelling using aquacyle In Proceedings of the 10thInternational Conference on Environmental Science ampTechnology Kos Island Greece 5ndash7 September 2007

Kenway SJ Priestley A Cook S Seo S Inman MGregory A and Hall M 2008 Energy use in theprovision and consumption of urban water in Australiaamp New Zealand Water for a Healthy country Flagshipreport series ISSN 1835ndash095X Water Service Associa-tion of Australia

Lundin M 2003 Indicators for measuring the sustainabilityof urban water system ndash A life cycle approach PhDdissertation Chalmers University of Technology

Makropoulos CK Memon FA Shirley-Smith C andButler D 2008a Futures An exploration of scenariosfor sustainable urban water management Water Policy10 345ndash373

Makropoulos CK Natsis K Liu S Mittas K andButler D 2008b Decision support for sustainableoption selection in integrated urban water managementEnvironmental Modelling amp Software 23 (12) 1448ndash1460

Mitchell V 2005 AquaCycle user guide A daily urban waterbalance model Australia Monash University Press

Mitchell V 2006 Applying integrated urban water manage-ment concepts A review of Australian experienceEnvironmental Management 37 (5) 589ndash605

Mitchell V Mein RG and McMahon TA 2001Modelling the urban water cycle Environmental Model-ling amp Software 16 615ndash629

Municipality of Tel Aviv 2006 City ndash The Strategic plan forTel Aviv Yafo Strategic Planning Unit Tel AvivMunicipality Israel

Urban Water Journal 117

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The main aim of this research is to develop urbanwater management strategies by applying the Aqua-Cycle model for the investigation of their effects on thesustainability of the water system of Tel Aviv Thesustainability is measured (among others) by indicatorswhich are related to the reduction of freshwaterconsumption energy use and the increase in theamount of wastewater reuse The research is aimed atproviding valuable information for decision makers inTel Aviv to steer the city towards sustainability in asituation of water scarcity

2 Methodology

21 Integration of strategic planning and modelsupported decision making

The methodology is a combination of strategicplanning as described in the Cities Alliance Guide toCity Development Strategies (Cities Alliance 2006) andthe application of a total urban water cycle model Themodel is used to assess the current situation as well asto evaluate future scenarios and strategies (Van derSteen and Howe 2009) The process is an integration ofengineering calculations and a stakeholder involve-ment process As a first step in the process amultistakeholder platform was established which wasnamed the Learning Alliance (or lsquoWater Clubrsquo) ALearning Alliance is an (informal) group of stake-holders that in Tel Aviv jointly (1) Assesses thecurrent shape of the urban water system and for-mulates un-sustainability factors (2) Develops a visionfor the future state of the urban water system (3)Translates the vision in a set of sustainability objectivesand indicators (4) Identifies possible future scenarioswhere scenarios are defined as possible futures that areout of the control by urban water managers such asclimate change (5) Formulates strategies aimed atachieving the vision and (6) Recommends an im-plementation plan to relevant planning authorities (seeFigure 1) (Butterworth et al 2008) The LA workshopswere complemented by collection of secondary datasite visits and by interviewing water sector profes-sionals on their views on the vision scenarios andstrategies The gathered data was used to prepare theinput files for AquaCycle to make a water balance Inaddition was calculated how much energy is requiredfor the various strategies (Figure 2)

22 AquaCycle

AquaCycle is a total urban water cycle modeldeveloped to take a more holistic view allowing watersupply wastewater disposal and storm water drainageto be considered as components within a single systemThe lsquocyclersquo starts with water entering as precipitation

or as (fresh) water imported in order to meet theindoor and outdoor water use requirement The waterthen passes through the households or other waterusers and exits in the form of evapotranspirationstorm water or wastewater (Mitchell 2005) AquaCycleoperates on three different scales (unit-block clusterand catchment) (see Figure 3) in order to enable thesimulation of any urban form The input data for themodel which uses a time step of one day includesclimate data indoor water use data and site character-istics Surfaces are divided into two categoriespervious and impervious Impervious surfaces includeroofs roads and pavement Pervious areas are house-hold gardens and open public space (parks) and aremodelled as single stores that overflow when full intothe drainage system Water evaporation from bothpervious and impervious areas is calculated accordingto daily potential evapotranspiration values Theamount of water imported into an area is the sum ofindoor water use irrigation and leakage The totalwastewater discharge from the catchment is the sum ofindoor water use infiltration and inflow from thestorm water drainage system (Mitchell 2005)

The application of AquaCycle to Tel Avivrsquos watersystem involved the determination of three groups of

Figure 1 Overview of (on-going) strategic planning exercisefor the water system of Tel Aviv

Figure 2 Procedures of research methodology (numberindicates order of the steps in the process)

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data meteorological data indoor water use profile andphysical site characteristics The details about datacollection and processing are presented below

23 Meteorological data

The climate data input file is a series of dailyprecipitation and potential evaporation figures from1994 to 2007 Precipitation data of Tel Aviv wasobtained directly from the European Climate Assess-ment amp Data set project (ECAampD 2008) Potentialevaporation data was estimated based on monthlyheat indexes and the equations presented by theThornthwaite method (Thornthwaite 1948) The timeseries was used to simulate future precipitation Forthe baseline scenario the time series was assumed torepeat itself in 2009ndash2022 2023ndash2036 etc For thelsquonormal scenariorsquo the time series was used without anyadjustments from 2009 to 2022 while precipitation wasreduced by 10 for the period 2023ndash2050 andtemperature was increased by 158C for the sameperiod For the lsquoextremersquo scenario the values were 15and 258C respectively The lsquonormalrsquo scenario is basedon the climate change estimation of the Israel Ministryof Environmental Protection (2008) The lsquoextremersquoscenario was included to investigate the response of theurban water system to more extreme climate change

24 Indoor water use profile

Average yearly household water consumption figureswere obtained from the municipality as well asconsumption figures for public buildings health carehotels businesses sport facilities security transportand construction Since AquaCycle only considerslsquohouseholdsrsquo as water consumers (apart from publicirrigation) it was assumed that households areconsuming the sum of the consumption in the sectorsmentioned above These figures include the consump-tion by the day-time residents The consumption per

household was calculated by dividing that sum bythe number of households The end-use of water inhouseholds (in kitchen bathroom garden etc) is notknown for Tel Aviv and therefore the indoor waterusage profile for kitchen bathroom laundry and toiletof Canberra (Mitchell 2005) was copied and adjustedpro rata to a total household consumption ascalculated for Tel Aviv

25 Physical site characteristics

The municipal boundaries of the city were taken as thecatchment boundary The catchment was divided intosix clusters These six clusters were formed by groupingthe 37 sub-catchments of the drainage system suchthat each group of sub-catchments equalled (as muchas possible) one of the city-quarters used by theStatistics department of the municipality Informationof total area population and land use by quarter (nownamed cluster) was available from the StatisticsDepartment and was used as input data for AquaCycle(Figure 4) The road area and the open space area ineach cluster were estimated based on satellite imagesmaps of land use and detailed information from theStrategic Planning Unit of Tel Aviv Municipality(Municipality of Tel Aviv 2006)

Though the study area includes residential com-mercial and public buildings it was assumed that allbuildings are residential buildings This assumption isin line with the previous assumption on the allocationof all water consumption (except public irrigation) tohouseholds Since most of the buildings in Tel Aviv areapartment blocks the assumption seems reasonableThe typical apartment block houses several householdunits (apartments) and one apartment is equal to oneunit-block in the model The number of unit-blocks ineach cluster was calculated by dividing the totalpopulation of a cluster by the average number ofoccupants per household (22 Statistics Department)The total area of unit-blocks in each cluster was

Figure 3 Spatial scales used in AquaCycle The area of garden roof and pavement in the unit-block in the model is asmeasured for the typical multi-unit apartment block but divided by the number of apartments in the block

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calculated based on the total area of a cluster minusthe area of roads and public open spaces The averagearea of one unit-block was obtained from the total areaof unit-blocks and the number of unit-blocks withinthe cluster Physical characteristics of a representativeapartment block were estimated by observation basedon satellite images and site visits It was estimated thatthe areas of roof garden and pavement per apartmentblock are 70 15 and 15 respectively The areas wereproportionally allocated to the apartments in the blockand therefore the percentages are also valid for theunit-blocks in the model

26 AquaCycle outputs and energy calculations

The output of the model is a water balance with dailyvalues for precipitation piped water supply evapo-transpiration stormwater drainage and wastewatercollection Monthly or yearly average values can becalculated for the catchment cluster or unit-blockscale The mass balance for the catchment scale wasused to calculate the total energy consumption of thesystem All components of the water system thatconsume energy were identified by interviewing staff ofTel Aviv municipality and the Mekorot company anddata on energy consumption (mostly in kWhm3) wereobtained

27 Formulation of scenarios

Scenarios were not formulated to predict the futurebut were used by the LA as tools for thinking about

possible futures and to evaluate the impact ofdecisions taken today on these futures Commonelements in the scenarios were based on regulatorysocial economic environmental and technical aspects(Makropoulos et al 2008a) but not all of theseelements can be modelled quantitatively In thiswork four quantitative scenarios were formulatedfor Tel Aviv until the year 2050 including fourfactors precipitation temperature population growthand urbanisation all of which can be simulated byAquaCycle simulation (see Table 1) All of thesefactors impact directly or indirectly on Tel Avivrsquosurban water system via the effects on water demandwater resources water infrastructure and urban sur-face permeability The baseline scenario describes thecurrent situation of the city The lsquonormalrsquo scenario isbased on estimations on climate change by IsraelMinistry of Environmental Protection (2008) Data onhistorical population growth rate (22) was obtainedfrom Tel Aviv Municipality The scenarios assumedthe same growth rate to continue until 2050 whichwould only be possible by densification and morehigh-rise buildings in the city In all scenariosdensification leads to a reduction in (permeable) publicopen space of 20

28 Formulation of strategies

The LA developed strategies to achieve the visiongiven the possible future scenarios through groupdiscussions and by one-on-one interviews Onlystrategies that could be simulated by AquaCycle arepresented here The strategies are

A Stormwater use and temporary aquifer storage

Measures for stormwater use and aquifer infiltrationprojects were simulated for each cluster The storm-water from the unit-blocks and from the roads drainedinto a stormwater storage tank in each cluster and wasreused for toilet flushing garden and public spaceirrigation Excess stormwater was infiltrated into theaquifer The stormwater surface storage volumesinitially used were cluster 1 15000 m3 cluster 25000 m3 cluster 3 15000 m3 cluster 4 15000 m3cluster 5 5000 m3 cluster 6 5000 m3 (based on theoptimisation routine of AquaCycle) A 10000 m3 ofaquifer storage was applied for each cluster The effectof increasing and decreasing these volumes wasinvestigated as well

B Rainwater harvesting

A rainwater tank of various sizes was applied atevery household in all clusters of the city Rain

Figure 4 Clusters defined for the Tel Aviv catchment(Numbers 1ndash6) and Tel Avivrsquos neighbouring municipalities

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water was used in the kitchen for laundry inthe bathroom for toilet flushing and for gardenirrigation

C Permeable pavement

Pavements in unit-block gardens and for roads werereplaced by permeable pavements simulated in Aqua-Cycle by increasing the garden and open space area inthe city

D Wastewater reuse at unit-block scale

Decentralised wastewater treatment units were appliedat every household in the city Wastewater fromkitchen bathroom and laundry was treated and reusedfor toilet flushing and garden irrigation It wasassumed that no water was lost in the treatmentprocess The storage volume for treated wastewater atevery household in each cluster was identified accord-ing to the optimisation results of AquaCycle (200 L ofwastewater storage per household in cluster 1 2 3 56 and 100 L of wastewater storage in cluster 4)

E Wastewater reuse at cluster scale

Wastewater treatment units were applied for eachcluster Household wastewater draining to a clusterwastewater storage tank was treated stored andsupplied for toilet flushing and garden irrigation forhouseholds and for open space irrigation It wasassumed that no water was lost in the treatmentprocess The treated wastewater storage volumes werecluster 1 7900 m3 cluster 2 4700 m3 cluster 38300 m3 cluster 4 1300 m3 cluster 5 9100 m3cluster 6 7200 m3 (based on the optimisation routineof AquaCycle)

29 Evaluation of strategies

As mentioned above the LA developed a vision for asustainable urban water system for the city This visionwas translated into tangible objectives the achieve-ment of which can be measured by sustainabilityindicators The score for these indicators were used toevaluate the strategies rather than by a thoroughengineering and economic feasibility study Some ofthe indicators could be evaluated in a quantitative wayusing the AquaCycle outputs others were evaluatedqualitatively

3 Results and discussion

31 Sustainability objectives and indicators

Based on interviews and general investigations it wasfound that the urban water system of Tel Aviv istypical for an advanced developed country but alsocharacterised by a number of un-sustainability factorswhich need improvement With regard to planning ofthe whole system it was noticed that lsquowater manage-mentrsquo is not addressed in the Strategic Plan of the city(Municipality of Tel Aviv 2006) and water indicatorsare therefore also not included in the set of indicatorsthat is used to monitor the development of the cityThis is somewhat surprising since the domestic waterconsumption in the city is higher than the amount thatcan be sustained from renewable water sources Thewater supply system is also threatened by insufficientmaintenance of the distribution system which causesbio-film growth and microbial pollution which in turnmay cause a higher chlorine demand One of theunderlying causes of the poor maintenance is lack ofsuitable financial resources for local government tomaintain the drinking water quality The same reasonsalso result in frequent leakages from the sewer system

Table 1 Formulated scenarios and factors until the year 2050

FactorPrecipitationdecrease

Temperatureincrease

Populationgrowth rate Urbanisation

Baseline scenario ndash ndash 22lsquoNo major changersquo scenario ndash ndash 22 20 of public open space is replaced

by residential area (10 in 2022 andanother 10 in 2046) road area isnot changed

lsquoNormalrsquo scenario 20 158C 22 20 of public open space is replacedby residential area (10 in 2022 andanother 10 in 2046) road area isnot changed

lsquoExtremersquo scenario 30 258C 22 20 of public open space is replacedby residential area (10 in 2022 andanother 10 in 2046) road area isnot changed

From 2023 onwards

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which causes severe pollution of the local aquiferwhich is one of the drinking water sources for the cityBasically all municipal wastewater is collected andtreated to a tertiary level but it is not utilised foragricultural irrigation within the region but in theNegev Urban parks in Tel Aviv are still irrigated withfresh water Stormwater is collected in a separatedrainage system but discharged directly to the seawithout any treatment There is no monitoring systemor research to evaluate the amount of stormwatergenerated in the city and its quality It is likely that TelAviv is overlooking the potential to use this nonconventional water resource The capacity of thedrainage system is not sufficient to prevent occasionalflooding Finally the un-sustainability of the systembecomes clear from the significant amount of energyused to transport fresh water over long distances anduphill (from the Sea of Galilee) to treat wastewater inan energy intensive system and finally to pump effluentto irrigation fields in the south of the country Thecommissioning of desalination plants will only increasethe energy consumption in the system

Based on this assessment the LA formulated aVision for sustainable urban water management in TelAviv lsquoTel Avivrsquos water system management will beestablished based on sustainability indicators andapply an efficient and integrated water managementto meet the water demand of citizens and for otherapplications with sufficient qualities and reasonableprices while the natural status of water resources isassuredrsquo The vision was translated into a set oftangible objectives and related indicators as shownin Table 2

32 Model calibration and simulation of wastewateroutput

The characteristics of the modelled clusters and therepresentative unit-block are outlined in Table 3 and 4The meteorological data the indoor water use profileand physical site characteristics were used as inputsfor the model The default calibration parameters(Table 5) initially were used and the model output interms of lsquoimported waterrsquo was compared with themunicipalities measured data on total water distrib-uted to the consumers The average amount oflsquoimported waterrsquo simulated by the model was about10 lower than the total water consumption Thelsquotrigger to irrigatersquo is the fraction of the optimal soilmoisture for plant growth which is still acceptable tothe user This trigger for private gardens and publicopen space was adjusted to 062 and as a result theaverage lsquoimported waterrsquo simulated by the model thenwas exactly the average volume of water distributed tothe consumers (Figure 5)

The monthly water consumption in the city isabout 40 higher in the summer irrigation seasonthan in the winter season The seasonal fluctuationcould be described well by the model throughirrigation of private gardens and public open spaceIt is likely that also the indoor water use is higher insummer but it is not possible in AquaCycle to changethe household indoor water consumption between theseasons Variation in imported water based on thefigures provided by the municipality (Figure 5) isrelatively large between some of the summer monthsespecially in 2004 and 2007 The reason for these largerfluctuations is unknown since the differences intemperature and potential evapotranspiration do notseem to explain such large fluctuations The model istherefore also not able to describe well these short-termfluctuations

Further calibration of the model was attemptedon observed wastewater flows from the wider TelAviv area (the Dan District) Unfortunately thewastewater flow from Tel Aviv is not measuredseparately from the wastewater flow from surround-ing municipalities It was therefore assumed that theamount of wastewater production per capita per yearin the various municipalities in the Dan District is thesame Therefore based on the population of TelAviv the amount of wastewater generated from TelAviv is estimated as 326 of total wastewaterproduction of the Dan District The wastewater flowssimulated by AquaCycle in the dry season (AprilndashOctober) were 18 lower than the flows based onmeasurements and the above described calculation(Figure 6) The simulated values may actually becloser to reality since the simulated values are90 of the indoor water consumption (about 31MCMmonth Figure 5) whereas the measured value(adjusted for population) is more than the actualindoor water consumption The higher flows inJanuary March and December are caused by wrongconnections between the stormwater drainage andfoul sewerage system The observed increase due tostormwater infiltration could be used to adjust thecalibration parameter lsquo of surface runoff as inflowrsquo(Table 5) The default value is 3 but a better fitwas achieved by using 7 This percentage is similarto the estimate of infiltration by Mekorot theoperator of the treatment plant (Aharoni personalcommunication)

33 The water balance of the system

The calibrated model was used to prepare the averageannual water balance for the city for the years2003ndash2007 (Figure 7) The water balance can be usedfor a fundamental evaluation of the sustainability of

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Table

2

Specificobjectives

andsustainabilityindicators

fortheurbanwatersystem

ofTel

Aviv

Specificobjective

Indicator

Unit

WaterPolicy

1TA

willraiseawarenessamongitscitizensabout

lsquowaterandsustainabilityrsquoandwillinvolvethe

publicin

decisionmaking

Thenumber

ofcitizensthatwillparticipate

inconsultativemeetings

Number

ofcitizensper

year

2TA

willmanageitsurbanwatersystem

inan

integratedwayintegratingaspects

ofwater

supplystorm

wateramp

wastew

atermanagem

ent

Theproductionofanintegratedurbanwater

managem

entplanforthecity

at2-yearintervals

Tim

elyproductionofintegratedplan

3A

setofsustainabilityindicators

willbeaccepted

andtheseindicators

willbeusedfordecision

makingandplanning

Referencesin

municipalplanningpolicy

documents

andgovernmentdecisionsto

the

sustainabilityindicators

Number

ofdocuments

withreferences

4TA

willstrengthen

thescientificbasisofitsdecision

makingconcerningthemanagem

entofitsUrban

WaterSystem

Thenumber

ofmunicipality

staffthatisusing

resultsfrom

scientificresearchin

theirdailywork

Number

ofstaff

WaterDem

andManagem

ent

5Thetotaldem

andin

TA

forfreshwateristo

be

reducedby10

by2050

Thereductionin

freshwatervolumeim

ported

tothecitycomparedto

the2009value

m3yearor

reduction

6Rainwaterandstorm

waterharvestingfor

non-potable

reuse

inthedomesticsectorwillbe

investigatedandapplied

ifoverallsustainability

ofthesystem

isincreased

Availabilityofastudyonrainwaterandor

storm

waterharvestingin

TA

Availabilityofstudy

Thenumber

ofhouseholdscollectingrainwater

Number

ofhouseholds

Thevolumeofrainwaterandorstorm

water

collectedandusedfornon-potable

use

m3year

7TA

willphase

outtheirrigationofurbanparks

withfreshwaterandwillonly

use

recycled

wastew

ater

forthispurpose

Thevolumeoffreshwaterorrecycled

wastew

aterusedforpark

irrigation

m3year

Percentageoftotalareairrigatedbyfreshwater

8

TA

willinfiltrate

storm

watergeneratedin

itsareainto

theaquiferherebyreducingthespillofwaterto

thesea

reducingthehydraulicloadto

theWWTPand

contributingto

aquifer

replenishmentTA

willtakecare

thatthestorm

waterisnotpolluted

Thepercentageofstorm

waterthatisinfiltrated

into

theaquifer

EnvironmentalProtection

9TA

willrestore

andprotect

itssurface

water

(YarkonRiver)

Thewaterquality

oftheYarkonriver

expressed

incommonly

usedwaterquality

parameters

(BODCOD)

various

10

TA

willminim

izetheenergyconsumptionin

theurban

watersystem

Thetotalquantity

ofenergyfrom

non-renew

able

sources

usedto

operate

theurbanwatersystem

includingwaterheatingin

thehouseholds

kWhyear

Socio-economy

11

TA

willsupply

waterofgoodquality

toitscitizens

atreasonable

price

insufficientqualities

ThefractionofsamplesanalyzedbytheMinistry

ofHealththatdoes

notsatisfythehealthcriteria

Thefrequency

ofsupply

interruptions

Downtimeper

year

12

TA

willensure

equityin

theaccessto

wateraswell

asto

irrigatedgreen

areas

Thespatialdistributionofwaterquality

and

frequency

ofserviceinterruptionsin

thecity

Mapwithwaterquality

andservice

interruptionfrequency

Thegreen

areaavailable

per

personandits

spatialdistribution

Mapwithm

2green

areaper

capita

13

TA

willreduce

therisk

offloodingin

vulnerable

arearsquos

toafrequency

thatisacceptable

toallstakeholderseven

under

future

clim

ate

changescenarios

Thenumber

ofpeople

affectedbyfloodingper

year

Number

ofpeople

per

year

Theeconomic

damagecausedbyflooding

USDyear

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ober

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the system The natural precipitation would not besufficient to satisfy current demand therefore largewater imports are required About 7 of the totalsystem inputs infiltrate into the groundwater andare in principle available for recovery from theaquifer In 2008 the municipality pumped slightlymore than 4 MCM from the aquifer therefore theTel Aviv urban area does not directly contribute toaquifer depletion The largest outflow from the city isthe wastewater flow which is treated and reused in theNegev The largest flux that is not beneficially used isthe stormwater flow If all stormwater would becaptured and used for urban purposes then about50 of the urban demand could be met by reclaimedstormwater

34 Results of the energy balance

The water balance for the city was used to calculatethe energy consumption in the urban water system(Figure 8) For each point of energy consumption inthe system the specific energy consumption in kWhm3

was determined as well as the proportion of the totalflow passing through that specific pathway Thus thetotal energy consumption in the system was calculatedas 328 kWhm3 This figure does not include energyconsumption for water heating in the householdThe largest energy consumption in the water systemitself is due to the long distance from the Lake ofGalilee seawater desalination wastewater treatmentand conveyance of effluent to the Negev The current

Table 3 Overview of cluster characteristics

Cluster 1 2 3 4 5 6

Population 80007 49095 84834 14384 91656 74964Total area (ha) 7451 6477 1459 6590 6470 9846Roads ( ha) 1135 976 1579 248 1180 1588Public open space (ha) 1490 648 2927 3927 647 646Unit-blocks (ha) 4825 4854 10084 2415 4643 7612

Table 4 Overview of unit-block characteristics

ClusterNumber ofunit-blocks

Averageoccupancy

Average areaof a unit-block (m2)

Area ofroof m2 (70)

Area ofgarden m2 (15)

Area ofpavement m2 (15)

1 36367 22 1327 929 199 1992 22316 22 2175 1523 326 3263 38561 22 2615 1831 392 3924 6538 22 3694 2586 554 5545 41662 22 1115 780 167 1676 34074 22 2234 1564 335 335

Table 5 Parameters used for the model calibration

Output Calibration parameter Default After calibration Units

Stormwater Percentage area of store 1 22 Pervious storage 1 capacity 32 mmPervious storage 2 capacity 240 mmRoof area maximum initial loss 0 mmEffective roof area 100 Paved area maximum initial loss 0 mmEffective paved area 100 Road area maximum initial loss 0 mmEffective road area 100 Base flow index 055 RatioBase flow recession constant 00025 Ratio

Wastewater Infiltration index 0095 RatioInfiltration store recession constant 012 Ratio of surface runoff as inflow 3 7

Imported water Garden trigger to irrigate 05 062 RatioPublic open space trigger to irrigate 042 062 Ratio

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contribution of desalination is small because only asmall fraction of the water use originates in desalina-tion plants but this is likely to increase in the futureNote that the specific energy consumption for desali-nation is several times the sum of all specific energyconsumption in the rest of the system

Figure 9 compares the energy consumption in TelAviv with some Australian cities (Kenway et al 2008)and with Zaragosa in Spain (SWITCH 2008 unpub-lished data) The energy costs in those cities for watertreatment and water pumping are highly variabledepending on quality and distance of the waterresource The energy consumption for wastewatertreatment and wastewater pumping (not includingconveyance to the Negev) is in the same range asobserved for the other cities

35 Evaluation of strategies ndash for the 2009 populationand average climatic conditions of 1994ndash2007

A Stormwater use and temporary aquifer storage

The number of days with rain in Tel Aviv is on average45 per year but only 31 days have more than 2 mm perday and therefore only a small number of days

Figure 5 Simulated volume of imported water and figures provided by the municipality from 2003 to 2007 (X-axis mmyy)

Figure 6 Total monthly wastewater production of Tel Aviv in year 2008 as estimated based on total Tel Avivrsquos share of totalDan Region wastewater production (lsquoEstimated datarsquo) and as simulated by AquaCycle

Figure 7 Tel Avivrsquos average water balance for 2003ndash2007(Stormwater flux includes the groundwater baseflow)

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generate significant runoff for stormwater harvestingAnother limiting factor in Tel Aviv is that the demandfor stormwater for irrigation is in the dry season whenthere is obviously no stormwater generation Still withthe cluster storage volumes indicated earlier (in total60000 m3 or 033 m3 per household) a reduction inwater import of 34 can be achieved Increasing totalstorage volume increases the percentage water savingbut reduces the efficiency of the tank (Figure 10) Aneconomic analysis is required to determine a feasiblevolume for the cluster stormwater tanks and this inturn determines the potential for water saving ofthis strategy Saving more than 5 by stormwaterharvesting is estimated to be very unlikely

B Rainwater harvesting

This strategy is more effective than strategy A in termsof overall water savings in the city and also moreefficient in terms of the volume of water saved per unit

rainwater tank volume (Figure 10) This difference iscaused by the higher quality of the rainwater whichallows (in this study) use for all household purposesFor a tank of 330 L per household the collectedrainwater is used for 32 and spilled from the tank for68 In strategy A the quality of the stormwater onlyallows use for toilet flushing and it is therefore mostlyspilled from the storage tanks during storm events (peryear 8 usage 92 spillage for the case with 033 m3

tank volume per household) In addition stormwaterin strategy A is in fact hardly used for irrigation sincethe storm events take place outside the irrigationseason Assuming that it is economical feasible toinstall a rainwater tank volume of about 075 m3 perhousehold then a total saving of 10 of water importsinto the city is possible Rozos et al (forthcoming)calculated that a 10 reduction of potable waterdemand in households in a Mediterranean climatewould increase the capital cost of the water supplysystem with about 40 while a 20 reduction in

Figure 8 The energy consuming components of Tel Avivrsquos water system

Figure 9 Energy use intensity of water and wastewater services by city (For Tel Aviv without energy consumption for theconveyance of effluent to irrigation areas in the Negev)Source Kenway et al (2008) SWITCH unpublished data

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demand would be achievable when accepting a 160cost increase (ie even larger storage tanks)

C Permeable pavement

The surface of Tel Aviv is for 30 permeable and 70impermeable according to the calculated and esti-mated physical characteristics of the city (Tables 3and 4) The impermeable surface consists for 33 ofroads and pavements which could be made permeableby application of permeable types of pavementsAssuming that 80 of the roads and pavements canbe made permeable then the total impermeablesurface has been reduced by 26 Simulation withthe model showed that this would result in a reductionin stormwater generation of 20 (from 177 to 141MCM per year) The reduction in stormwater genera-tion is not only due to increased infiltration becausethe model simulates infiltration to increase onlyfrom 23 to 38 MCM per year The rest of thestormwater evaporates from the soil moisture storeand overflows via pervious surface runoff into thedrainage system

The purpose of this strategy would be to increaseaquifer recharge to allow more aquifer abstractionThe extra volume of abstraction per m2 of made-permeable pavement is about 02 m3m2 per yearA financial analysis will most likely show thatthis strategy is not feasible from a financial pointof view

D Wastewater reuse at unit-block scale

The model simulated grey wastewater treatmentstorage and reuse at household scale The storage

tank volumes based on the AquaCycle optimisationroutine resulted in a 21 reduced demand forimported water (99 MCM ) and a 27 reduction inwastewater flows from the city (94 MCM) Spillagefrom the tanks was small and therefore doubling thetank volumes changed the savings to 23 and 29 onlyrespectively Benefits of this strategy are reduced totaldemand which reduces the need for seawater desalina-tion and cost savings for wastewater collection andtreatment Costs of this strategy include costs forthe household-scale treatment and reuse system andthe reduction in effluent availability for agriculturein the Negev Potential health risks from wastewaterstorage and treatment at household and from potentialcross connections in double distribution networksshould also be addressed

E Wastewater reuse at cluster scale

The model simulated grey wastewater treatment andstorage at cluster level and reuse for toilet flushingirrigation of gardens and irrigation of open publicspace The storage tank volumes based on theAquaCycle optimisation routine resulted in a 25reduced demand for imported water (115 MCM )and a 31 reduction in wastewater flows from thecity (108 MCM) Doubling the tank volumeschanged the savings to 32 and 40 respectivelyThe saving of imported water per unit volumestorage tank for the smaller (021 m3household)and larger (042 m3 per household) tanks were 300and 194 m3m3 per year respectively Comparingthese figures to stormwater strategies A and B(Figure 10) clearly shows that wastewater reuse hasmore potential to save imported water and requires

Figure 10 Potential for yearly water saving by implementation of strategies A and B (for the 2009 population and averageclimatic conditions of 1994ndash2007)

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smaller tanks Reason for this difference is thatwastewater supply to the storage tanks is much lessfluctuating than stormwater flows

36 Evaluation of strategies under scenarios till2050 ndash demand for imported water (Indicator 5)

The demand for imported water in the city under thebaseline scenario increases from 472 MCM in 2009 to759 MCM in 2050 (Figure 11) due to populationgrowth The other scenarios slightly increase thedemand for imported water (778 MCM in 2050 forthe extreme scenario) The effect of climate change issmaller than one would maybe expect because thereduction in rainfall in the wet season does not increasethe demand for irrigation water since that demand isthere only in the dry season The increase intemperature during the dry season increases the

evapotranspiration and demand for irrigation waterbut only to a limited extend

The volume of water saved by the differentstrategies is constant with time for the lsquobaselinersquo andlsquono major changersquo scenarios but is affected by thechange in precipitation and temperature in the otherscenarios The volume of water saved by the strategy B(rainwater harvesting) will be less under the latterscenarios because the rainfall is less Figure 11 alsoshows that the volume of water saved in that strategyfluctuates from year to year with the fluctuations inyearly rainfall

The timing of the implementation of the strategiescould be based on keeping the total demand forimported water under a certain level Figure 12 showshow implementation of strategies B and D partlycancels the increase in demand due to populationgrowth

Figure 12 The simulated import of fresh water into Tel Aviv until 2050 based on phased implementation of strategies B and Dunder lsquonormalrsquo and lsquoextremersquo scenarios

Figure 11 The simulated import of fresh water into Tel Aviv until 2050 based on the lsquonormalrsquo scenario and different strategiesEmpirical data for 1996ndash2006 is also shown (source TahalMunicipality of Tel Aviv)

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37 Evaluation of strategies under scenarios till2050 ndash other indicators

Energy consumption per volume of water consumedcould be reduced by various measures such asreduction of physical leakage (Colombo et al 2002)or by optimising pump technology and pumpingschedules Energy consumption of the alternativestrategies was calculated to investigate their effecton the nexus water ndash energy The energy consumptionin the whole urban water system (Table 6) per m3

of water used (imported thorn reused water) in the citywas on average 289 kWh per m3 for the period2009ndash2050 (baseline scenario) Implementation of thestrategies affected the energy consumption in differentways Strategy B with a 330-L tank per householdresults in 274 kWhm3 mainly because rainwatersystems are estimated to use 0278 KWhm3 (Kenwayet al 2008) which is less energy intensive thenimporting water Wastewater treatment and reuse atcluster scale (strategy E 210-L tank per household)reduces energy consumption to 245 kWhm3 but thesame strategy at household (strategy D 200-L tankper household in cluster 1 2 3 5 6 and 100 L incluster 4) scale increases energy consumption till 318kWhm3 This is due to the higher energy con-sumption for on-site wastewater treatment systems(4 kWhm3 Steendam 2009) than for small waste-water treatment plants (estimated as 08 kWhm3

based on a reported range of 039 to 117 kWhm3 by

Young and Koopman 1991) Therefore it seems thatstrategy D performs best for both saving water andsaving energy

Implementation of the strategies will clearly affectsome of the indicators (Table 2 indicators 5 6 7 810) while other indicators are conditions for successfulimplementation (indicators 1 2 4 6) rather thanresults and yet other indicators are not likely to beaffected (indicators 11 12 13) The effect of thestrategies on groundwater quality and receiving surfacewater quality (indicator 9) is unsure and the topic ofongoing investigations

4 Conclusions

Based on the investigation of Tel Avivrsquos urban watersystem and the simulation results of AquaCyclefollowing conclusions are drawn

The volume of water imported into the city (onaverage 47 MCM per year) and the seasonalfluctuations in the period 2003ndash2007 was accu-rately described by the AquaCycle model usingthe input files on climate physical characteristicsof the city surface and average figures fordomestic end-use categories

Evaluation of several strategies to improve thesustainability of the water system showedthat rainwater harvesting from roofs for non-

Table 6 Energy consumption inventory of Tel Avivrsquos water system

Energy consumption(KWhm3)

Proportion oftotal amount

of water Source of data

Pumping water from the Lake ofGalilee to the city

13 90 Mekorot Company

Treating water from the Lake of Galilee 0 100 Mekorot Company(negligible since supplied toconsumer without treatment)

Treating amp pumping Sea water 39 2 Mekorot CompanyPumping groundwater from local wells 0371 8 Tel Aviv MunicipalityTreating groundwater from local wells 0 8 Tel Aviv Municipality

(negligible since supplied toconsumer without treatment)

Pumping for distributing water ndash North area 0103 135 Tel Aviv MunicipalityPumping for distributing water ndash South area 0077 72 Tel Aviv MunicipalityHeating water at household 407 27 EstimationWastewater collection 0111 100 Tel Aviv MunicipalityWastewater treatment 0425 100 Mekorot CompanyPumping treated wastewater for irrigation 145 100 Mekorot CompanyPumping stormwater 0 100 Tel Aviv Municipality

(negligible since dischargeddirectly to the Sea by gravity)

Total ( including heating water at household) 1427Total (not including household heating water ) 328

It was assumed that all water supplied by Mekorot to the city was taken from the Lake of Galilee rather than from groundwater pumpingstations closer to the city (such as Rosh HaAyin)

Based on 1 m3 supplied collected treated and reused

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potable reuse in households is more promisingthan stormwater collection and reuse at clusterscale Assuming that it is feasible to install arainwater tank volume of about 075 m3 perhousehold then a total saving of 10 of waterimports into the city is possible

The overall water mass balance for the cityshowed that this rainwater harvesting strategywould reduce the amount of stormwater thatleaves the city per year from 22 MCM toabout 17 MCM which shows that othertechnologies or approaches are necessary ifone would like to make full beneficial use ofthis resource

Increasing rainwater infiltration for aquiferrecharge is most likely not financially sustainablesince the extra volume of recharge to allow moreaquifer abstraction is only 02 m3year per m2 ofmade-permeable pavement

The largest saving of water imports could beachieved by wastewater reuse for urban non-potable uses Wastewater collection storage(042 m3 per household) treatment and reuse atcluster scale is simulated to result in a 32 and40 reduction in water imports and wastewaterflows respectively

The most important factor of future scenariosfor water demand is population growth Effectsof climate change (reduced rainfall to a max-imum of 30 and increase in temperature to amaximum of 258C) on imported water weremuch smaller not more than 25 increase inthe extreme scenario This is in agreement withRozos et al (forthcoming) who have estimatedfor a Mediterranean climate an increase between0 and 4 depending on the capacity of therainwater harvesting scheme

Energy consumption in the urban water systemwas calculated as 289 kWh per m3 of volume ofwater used (import thorn reuse) in the city forthe period 2009ndash2050 Implementation of thestrategies affects the energy consumption indifferent ways Rainwater harvesting has somepotential to reduce energy consumption (to 274kWh per m3) but the best strategy in thisrespect is wastewater treatment and reuse atcluster scale (245 kWh per m3) The samestrategy at household scale causes an increasein energy consumption (318 kWh per m3)

The results of the model and the scenarioplanning study can be used to score a numberof the suggested sustainability indicators for theurban water system of Tel Aviv and as such canbe used by the multidisciplinary Water Club tosteer the city towards sustainability

Acknowledgements

The authors would like to thank the Dutch governmentfor its support through the NPT programme andthe European Commission for its support through theSWITCH project (FP6 Global Change and Ecosystems018530)

References

Butterworth JA Sutherland A Manning N Darteh BDziegielewska-Geitz M Eckart J Batchelor CMoriarty P Schouten T Da Silva C Verhagen Jand Bury PJ 2008 Building more effective partnershipsfor innovation in urban water management In Interna-tional Conference on Water and Urban DevelopmentParadigms Towards an integration of engineering designand management approaches 15ndash19 September 2008Katholieke Universiteit Leuven Belgium

Cities Alliance 2006 Guide to City Development StrategiesImproving urban performance Washington DC USApp 92

Colombo AF and Karney BW 2002 Energy and costs ofleaky pipes Toward comprehensive picture ASCEJournal of Water Resources Planning and Management128 (6) 441ndash450

ECAampD (European Climate Assessment amp Dataset Project)2008 Data records httpecaknminl [AccessedApril 2010]

Israel Ministry of Environmental Protection 2008 Israelrsquosadaption to climate change ndash Impacts and recommenda-tion httpwwwsvivagovil [Accessed April 2010]

Karka P Manoli E Lekkas DF and AssimacopoulosD 2007 A case study on integrated urban watermodelling using aquacyle In Proceedings of the 10thInternational Conference on Environmental Science ampTechnology Kos Island Greece 5ndash7 September 2007

Kenway SJ Priestley A Cook S Seo S Inman MGregory A and Hall M 2008 Energy use in theprovision and consumption of urban water in Australiaamp New Zealand Water for a Healthy country Flagshipreport series ISSN 1835ndash095X Water Service Associa-tion of Australia

Lundin M 2003 Indicators for measuring the sustainabilityof urban water system ndash A life cycle approach PhDdissertation Chalmers University of Technology

Makropoulos CK Memon FA Shirley-Smith C andButler D 2008a Futures An exploration of scenariosfor sustainable urban water management Water Policy10 345ndash373

Makropoulos CK Natsis K Liu S Mittas K andButler D 2008b Decision support for sustainableoption selection in integrated urban water managementEnvironmental Modelling amp Software 23 (12) 1448ndash1460

Mitchell V 2005 AquaCycle user guide A daily urban waterbalance model Australia Monash University Press

Mitchell V 2006 Applying integrated urban water manage-ment concepts A review of Australian experienceEnvironmental Management 37 (5) 589ndash605

Mitchell V Mein RG and McMahon TA 2001Modelling the urban water cycle Environmental Model-ling amp Software 16 615ndash629

Municipality of Tel Aviv 2006 City ndash The Strategic plan forTel Aviv Yafo Strategic Planning Unit Tel AvivMunicipality Israel

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data meteorological data indoor water use profile andphysical site characteristics The details about datacollection and processing are presented below

23 Meteorological data

The climate data input file is a series of dailyprecipitation and potential evaporation figures from1994 to 2007 Precipitation data of Tel Aviv wasobtained directly from the European Climate Assess-ment amp Data set project (ECAampD 2008) Potentialevaporation data was estimated based on monthlyheat indexes and the equations presented by theThornthwaite method (Thornthwaite 1948) The timeseries was used to simulate future precipitation Forthe baseline scenario the time series was assumed torepeat itself in 2009ndash2022 2023ndash2036 etc For thelsquonormal scenariorsquo the time series was used without anyadjustments from 2009 to 2022 while precipitation wasreduced by 10 for the period 2023ndash2050 andtemperature was increased by 158C for the sameperiod For the lsquoextremersquo scenario the values were 15and 258C respectively The lsquonormalrsquo scenario is basedon the climate change estimation of the Israel Ministryof Environmental Protection (2008) The lsquoextremersquoscenario was included to investigate the response of theurban water system to more extreme climate change

24 Indoor water use profile

Average yearly household water consumption figureswere obtained from the municipality as well asconsumption figures for public buildings health carehotels businesses sport facilities security transportand construction Since AquaCycle only considerslsquohouseholdsrsquo as water consumers (apart from publicirrigation) it was assumed that households areconsuming the sum of the consumption in the sectorsmentioned above These figures include the consump-tion by the day-time residents The consumption per

household was calculated by dividing that sum bythe number of households The end-use of water inhouseholds (in kitchen bathroom garden etc) is notknown for Tel Aviv and therefore the indoor waterusage profile for kitchen bathroom laundry and toiletof Canberra (Mitchell 2005) was copied and adjustedpro rata to a total household consumption ascalculated for Tel Aviv

25 Physical site characteristics

The municipal boundaries of the city were taken as thecatchment boundary The catchment was divided intosix clusters These six clusters were formed by groupingthe 37 sub-catchments of the drainage system suchthat each group of sub-catchments equalled (as muchas possible) one of the city-quarters used by theStatistics department of the municipality Informationof total area population and land use by quarter (nownamed cluster) was available from the StatisticsDepartment and was used as input data for AquaCycle(Figure 4) The road area and the open space area ineach cluster were estimated based on satellite imagesmaps of land use and detailed information from theStrategic Planning Unit of Tel Aviv Municipality(Municipality of Tel Aviv 2006)

Though the study area includes residential com-mercial and public buildings it was assumed that allbuildings are residential buildings This assumption isin line with the previous assumption on the allocationof all water consumption (except public irrigation) tohouseholds Since most of the buildings in Tel Aviv areapartment blocks the assumption seems reasonableThe typical apartment block houses several householdunits (apartments) and one apartment is equal to oneunit-block in the model The number of unit-blocks ineach cluster was calculated by dividing the totalpopulation of a cluster by the average number ofoccupants per household (22 Statistics Department)The total area of unit-blocks in each cluster was

Figure 3 Spatial scales used in AquaCycle The area of garden roof and pavement in the unit-block in the model is asmeasured for the typical multi-unit apartment block but divided by the number of apartments in the block

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calculated based on the total area of a cluster minusthe area of roads and public open spaces The averagearea of one unit-block was obtained from the total areaof unit-blocks and the number of unit-blocks withinthe cluster Physical characteristics of a representativeapartment block were estimated by observation basedon satellite images and site visits It was estimated thatthe areas of roof garden and pavement per apartmentblock are 70 15 and 15 respectively The areas wereproportionally allocated to the apartments in the blockand therefore the percentages are also valid for theunit-blocks in the model

26 AquaCycle outputs and energy calculations

The output of the model is a water balance with dailyvalues for precipitation piped water supply evapo-transpiration stormwater drainage and wastewatercollection Monthly or yearly average values can becalculated for the catchment cluster or unit-blockscale The mass balance for the catchment scale wasused to calculate the total energy consumption of thesystem All components of the water system thatconsume energy were identified by interviewing staff ofTel Aviv municipality and the Mekorot company anddata on energy consumption (mostly in kWhm3) wereobtained

27 Formulation of scenarios

Scenarios were not formulated to predict the futurebut were used by the LA as tools for thinking about

possible futures and to evaluate the impact ofdecisions taken today on these futures Commonelements in the scenarios were based on regulatorysocial economic environmental and technical aspects(Makropoulos et al 2008a) but not all of theseelements can be modelled quantitatively In thiswork four quantitative scenarios were formulatedfor Tel Aviv until the year 2050 including fourfactors precipitation temperature population growthand urbanisation all of which can be simulated byAquaCycle simulation (see Table 1) All of thesefactors impact directly or indirectly on Tel Avivrsquosurban water system via the effects on water demandwater resources water infrastructure and urban sur-face permeability The baseline scenario describes thecurrent situation of the city The lsquonormalrsquo scenario isbased on estimations on climate change by IsraelMinistry of Environmental Protection (2008) Data onhistorical population growth rate (22) was obtainedfrom Tel Aviv Municipality The scenarios assumedthe same growth rate to continue until 2050 whichwould only be possible by densification and morehigh-rise buildings in the city In all scenariosdensification leads to a reduction in (permeable) publicopen space of 20

28 Formulation of strategies

The LA developed strategies to achieve the visiongiven the possible future scenarios through groupdiscussions and by one-on-one interviews Onlystrategies that could be simulated by AquaCycle arepresented here The strategies are

A Stormwater use and temporary aquifer storage

Measures for stormwater use and aquifer infiltrationprojects were simulated for each cluster The storm-water from the unit-blocks and from the roads drainedinto a stormwater storage tank in each cluster and wasreused for toilet flushing garden and public spaceirrigation Excess stormwater was infiltrated into theaquifer The stormwater surface storage volumesinitially used were cluster 1 15000 m3 cluster 25000 m3 cluster 3 15000 m3 cluster 4 15000 m3cluster 5 5000 m3 cluster 6 5000 m3 (based on theoptimisation routine of AquaCycle) A 10000 m3 ofaquifer storage was applied for each cluster The effectof increasing and decreasing these volumes wasinvestigated as well

B Rainwater harvesting

A rainwater tank of various sizes was applied atevery household in all clusters of the city Rain

Figure 4 Clusters defined for the Tel Aviv catchment(Numbers 1ndash6) and Tel Avivrsquos neighbouring municipalities

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water was used in the kitchen for laundry inthe bathroom for toilet flushing and for gardenirrigation

C Permeable pavement

Pavements in unit-block gardens and for roads werereplaced by permeable pavements simulated in Aqua-Cycle by increasing the garden and open space area inthe city

D Wastewater reuse at unit-block scale

Decentralised wastewater treatment units were appliedat every household in the city Wastewater fromkitchen bathroom and laundry was treated and reusedfor toilet flushing and garden irrigation It wasassumed that no water was lost in the treatmentprocess The storage volume for treated wastewater atevery household in each cluster was identified accord-ing to the optimisation results of AquaCycle (200 L ofwastewater storage per household in cluster 1 2 3 56 and 100 L of wastewater storage in cluster 4)

E Wastewater reuse at cluster scale

Wastewater treatment units were applied for eachcluster Household wastewater draining to a clusterwastewater storage tank was treated stored andsupplied for toilet flushing and garden irrigation forhouseholds and for open space irrigation It wasassumed that no water was lost in the treatmentprocess The treated wastewater storage volumes werecluster 1 7900 m3 cluster 2 4700 m3 cluster 38300 m3 cluster 4 1300 m3 cluster 5 9100 m3cluster 6 7200 m3 (based on the optimisation routineof AquaCycle)

29 Evaluation of strategies

As mentioned above the LA developed a vision for asustainable urban water system for the city This visionwas translated into tangible objectives the achieve-ment of which can be measured by sustainabilityindicators The score for these indicators were used toevaluate the strategies rather than by a thoroughengineering and economic feasibility study Some ofthe indicators could be evaluated in a quantitative wayusing the AquaCycle outputs others were evaluatedqualitatively

3 Results and discussion

31 Sustainability objectives and indicators

Based on interviews and general investigations it wasfound that the urban water system of Tel Aviv istypical for an advanced developed country but alsocharacterised by a number of un-sustainability factorswhich need improvement With regard to planning ofthe whole system it was noticed that lsquowater manage-mentrsquo is not addressed in the Strategic Plan of the city(Municipality of Tel Aviv 2006) and water indicatorsare therefore also not included in the set of indicatorsthat is used to monitor the development of the cityThis is somewhat surprising since the domestic waterconsumption in the city is higher than the amount thatcan be sustained from renewable water sources Thewater supply system is also threatened by insufficientmaintenance of the distribution system which causesbio-film growth and microbial pollution which in turnmay cause a higher chlorine demand One of theunderlying causes of the poor maintenance is lack ofsuitable financial resources for local government tomaintain the drinking water quality The same reasonsalso result in frequent leakages from the sewer system

Table 1 Formulated scenarios and factors until the year 2050

FactorPrecipitationdecrease

Temperatureincrease

Populationgrowth rate Urbanisation

Baseline scenario ndash ndash 22lsquoNo major changersquo scenario ndash ndash 22 20 of public open space is replaced

by residential area (10 in 2022 andanother 10 in 2046) road area isnot changed

lsquoNormalrsquo scenario 20 158C 22 20 of public open space is replacedby residential area (10 in 2022 andanother 10 in 2046) road area isnot changed

lsquoExtremersquo scenario 30 258C 22 20 of public open space is replacedby residential area (10 in 2022 andanother 10 in 2046) road area isnot changed

From 2023 onwards

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which causes severe pollution of the local aquiferwhich is one of the drinking water sources for the cityBasically all municipal wastewater is collected andtreated to a tertiary level but it is not utilised foragricultural irrigation within the region but in theNegev Urban parks in Tel Aviv are still irrigated withfresh water Stormwater is collected in a separatedrainage system but discharged directly to the seawithout any treatment There is no monitoring systemor research to evaluate the amount of stormwatergenerated in the city and its quality It is likely that TelAviv is overlooking the potential to use this nonconventional water resource The capacity of thedrainage system is not sufficient to prevent occasionalflooding Finally the un-sustainability of the systembecomes clear from the significant amount of energyused to transport fresh water over long distances anduphill (from the Sea of Galilee) to treat wastewater inan energy intensive system and finally to pump effluentto irrigation fields in the south of the country Thecommissioning of desalination plants will only increasethe energy consumption in the system

Based on this assessment the LA formulated aVision for sustainable urban water management in TelAviv lsquoTel Avivrsquos water system management will beestablished based on sustainability indicators andapply an efficient and integrated water managementto meet the water demand of citizens and for otherapplications with sufficient qualities and reasonableprices while the natural status of water resources isassuredrsquo The vision was translated into a set oftangible objectives and related indicators as shownin Table 2

32 Model calibration and simulation of wastewateroutput

The characteristics of the modelled clusters and therepresentative unit-block are outlined in Table 3 and 4The meteorological data the indoor water use profileand physical site characteristics were used as inputsfor the model The default calibration parameters(Table 5) initially were used and the model output interms of lsquoimported waterrsquo was compared with themunicipalities measured data on total water distrib-uted to the consumers The average amount oflsquoimported waterrsquo simulated by the model was about10 lower than the total water consumption Thelsquotrigger to irrigatersquo is the fraction of the optimal soilmoisture for plant growth which is still acceptable tothe user This trigger for private gardens and publicopen space was adjusted to 062 and as a result theaverage lsquoimported waterrsquo simulated by the model thenwas exactly the average volume of water distributed tothe consumers (Figure 5)

The monthly water consumption in the city isabout 40 higher in the summer irrigation seasonthan in the winter season The seasonal fluctuationcould be described well by the model throughirrigation of private gardens and public open spaceIt is likely that also the indoor water use is higher insummer but it is not possible in AquaCycle to changethe household indoor water consumption between theseasons Variation in imported water based on thefigures provided by the municipality (Figure 5) isrelatively large between some of the summer monthsespecially in 2004 and 2007 The reason for these largerfluctuations is unknown since the differences intemperature and potential evapotranspiration do notseem to explain such large fluctuations The model istherefore also not able to describe well these short-termfluctuations

Further calibration of the model was attemptedon observed wastewater flows from the wider TelAviv area (the Dan District) Unfortunately thewastewater flow from Tel Aviv is not measuredseparately from the wastewater flow from surround-ing municipalities It was therefore assumed that theamount of wastewater production per capita per yearin the various municipalities in the Dan District is thesame Therefore based on the population of TelAviv the amount of wastewater generated from TelAviv is estimated as 326 of total wastewaterproduction of the Dan District The wastewater flowssimulated by AquaCycle in the dry season (AprilndashOctober) were 18 lower than the flows based onmeasurements and the above described calculation(Figure 6) The simulated values may actually becloser to reality since the simulated values are90 of the indoor water consumption (about 31MCMmonth Figure 5) whereas the measured value(adjusted for population) is more than the actualindoor water consumption The higher flows inJanuary March and December are caused by wrongconnections between the stormwater drainage andfoul sewerage system The observed increase due tostormwater infiltration could be used to adjust thecalibration parameter lsquo of surface runoff as inflowrsquo(Table 5) The default value is 3 but a better fitwas achieved by using 7 This percentage is similarto the estimate of infiltration by Mekorot theoperator of the treatment plant (Aharoni personalcommunication)

33 The water balance of the system

The calibrated model was used to prepare the averageannual water balance for the city for the years2003ndash2007 (Figure 7) The water balance can be usedfor a fundamental evaluation of the sustainability of

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Table

2

Specificobjectives

andsustainabilityindicators

fortheurbanwatersystem

ofTel

Aviv

Specificobjective

Indicator

Unit

WaterPolicy

1TA

willraiseawarenessamongitscitizensabout

lsquowaterandsustainabilityrsquoandwillinvolvethe

publicin

decisionmaking

Thenumber

ofcitizensthatwillparticipate

inconsultativemeetings

Number

ofcitizensper

year

2TA

willmanageitsurbanwatersystem

inan

integratedwayintegratingaspects

ofwater

supplystorm

wateramp

wastew

atermanagem

ent

Theproductionofanintegratedurbanwater

managem

entplanforthecity

at2-yearintervals

Tim

elyproductionofintegratedplan

3A

setofsustainabilityindicators

willbeaccepted

andtheseindicators

willbeusedfordecision

makingandplanning

Referencesin

municipalplanningpolicy

documents

andgovernmentdecisionsto

the

sustainabilityindicators

Number

ofdocuments

withreferences

4TA

willstrengthen

thescientificbasisofitsdecision

makingconcerningthemanagem

entofitsUrban

WaterSystem

Thenumber

ofmunicipality

staffthatisusing

resultsfrom

scientificresearchin

theirdailywork

Number

ofstaff

WaterDem

andManagem

ent

5Thetotaldem

andin

TA

forfreshwateristo

be

reducedby10

by2050

Thereductionin

freshwatervolumeim

ported

tothecitycomparedto

the2009value

m3yearor

reduction

6Rainwaterandstorm

waterharvestingfor

non-potable

reuse

inthedomesticsectorwillbe

investigatedandapplied

ifoverallsustainability

ofthesystem

isincreased

Availabilityofastudyonrainwaterandor

storm

waterharvestingin

TA

Availabilityofstudy

Thenumber

ofhouseholdscollectingrainwater

Number

ofhouseholds

Thevolumeofrainwaterandorstorm

water

collectedandusedfornon-potable

use

m3year

7TA

willphase

outtheirrigationofurbanparks

withfreshwaterandwillonly

use

recycled

wastew

ater

forthispurpose

Thevolumeoffreshwaterorrecycled

wastew

aterusedforpark

irrigation

m3year

Percentageoftotalareairrigatedbyfreshwater

8

TA

willinfiltrate

storm

watergeneratedin

itsareainto

theaquiferherebyreducingthespillofwaterto

thesea

reducingthehydraulicloadto

theWWTPand

contributingto

aquifer

replenishmentTA

willtakecare

thatthestorm

waterisnotpolluted

Thepercentageofstorm

waterthatisinfiltrated

into

theaquifer

EnvironmentalProtection

9TA

willrestore

andprotect

itssurface

water

(YarkonRiver)

Thewaterquality

oftheYarkonriver

expressed

incommonly

usedwaterquality

parameters

(BODCOD)

various

10

TA

willminim

izetheenergyconsumptionin

theurban

watersystem

Thetotalquantity

ofenergyfrom

non-renew

able

sources

usedto

operate

theurbanwatersystem

includingwaterheatingin

thehouseholds

kWhyear

Socio-economy

11

TA

willsupply

waterofgoodquality

toitscitizens

atreasonable

price

insufficientqualities

ThefractionofsamplesanalyzedbytheMinistry

ofHealththatdoes

notsatisfythehealthcriteria

Thefrequency

ofsupply

interruptions

Downtimeper

year

12

TA

willensure

equityin

theaccessto

wateraswell

asto

irrigatedgreen

areas

Thespatialdistributionofwaterquality

and

frequency

ofserviceinterruptionsin

thecity

Mapwithwaterquality

andservice

interruptionfrequency

Thegreen

areaavailable

per

personandits

spatialdistribution

Mapwithm

2green

areaper

capita

13

TA

willreduce

therisk

offloodingin

vulnerable

arearsquos

toafrequency

thatisacceptable

toallstakeholderseven

under

future

clim

ate

changescenarios

Thenumber

ofpeople

affectedbyfloodingper

year

Number

ofpeople

per

year

Theeconomic

damagecausedbyflooding

USDyear

110 TTH Duong et al

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the system The natural precipitation would not besufficient to satisfy current demand therefore largewater imports are required About 7 of the totalsystem inputs infiltrate into the groundwater andare in principle available for recovery from theaquifer In 2008 the municipality pumped slightlymore than 4 MCM from the aquifer therefore theTel Aviv urban area does not directly contribute toaquifer depletion The largest outflow from the city isthe wastewater flow which is treated and reused in theNegev The largest flux that is not beneficially used isthe stormwater flow If all stormwater would becaptured and used for urban purposes then about50 of the urban demand could be met by reclaimedstormwater

34 Results of the energy balance

The water balance for the city was used to calculatethe energy consumption in the urban water system(Figure 8) For each point of energy consumption inthe system the specific energy consumption in kWhm3

was determined as well as the proportion of the totalflow passing through that specific pathway Thus thetotal energy consumption in the system was calculatedas 328 kWhm3 This figure does not include energyconsumption for water heating in the householdThe largest energy consumption in the water systemitself is due to the long distance from the Lake ofGalilee seawater desalination wastewater treatmentand conveyance of effluent to the Negev The current

Table 3 Overview of cluster characteristics

Cluster 1 2 3 4 5 6

Population 80007 49095 84834 14384 91656 74964Total area (ha) 7451 6477 1459 6590 6470 9846Roads ( ha) 1135 976 1579 248 1180 1588Public open space (ha) 1490 648 2927 3927 647 646Unit-blocks (ha) 4825 4854 10084 2415 4643 7612

Table 4 Overview of unit-block characteristics

ClusterNumber ofunit-blocks

Averageoccupancy

Average areaof a unit-block (m2)

Area ofroof m2 (70)

Area ofgarden m2 (15)

Area ofpavement m2 (15)

1 36367 22 1327 929 199 1992 22316 22 2175 1523 326 3263 38561 22 2615 1831 392 3924 6538 22 3694 2586 554 5545 41662 22 1115 780 167 1676 34074 22 2234 1564 335 335

Table 5 Parameters used for the model calibration

Output Calibration parameter Default After calibration Units

Stormwater Percentage area of store 1 22 Pervious storage 1 capacity 32 mmPervious storage 2 capacity 240 mmRoof area maximum initial loss 0 mmEffective roof area 100 Paved area maximum initial loss 0 mmEffective paved area 100 Road area maximum initial loss 0 mmEffective road area 100 Base flow index 055 RatioBase flow recession constant 00025 Ratio

Wastewater Infiltration index 0095 RatioInfiltration store recession constant 012 Ratio of surface runoff as inflow 3 7

Imported water Garden trigger to irrigate 05 062 RatioPublic open space trigger to irrigate 042 062 Ratio

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contribution of desalination is small because only asmall fraction of the water use originates in desalina-tion plants but this is likely to increase in the futureNote that the specific energy consumption for desali-nation is several times the sum of all specific energyconsumption in the rest of the system

Figure 9 compares the energy consumption in TelAviv with some Australian cities (Kenway et al 2008)and with Zaragosa in Spain (SWITCH 2008 unpub-lished data) The energy costs in those cities for watertreatment and water pumping are highly variabledepending on quality and distance of the waterresource The energy consumption for wastewatertreatment and wastewater pumping (not includingconveyance to the Negev) is in the same range asobserved for the other cities

35 Evaluation of strategies ndash for the 2009 populationand average climatic conditions of 1994ndash2007

A Stormwater use and temporary aquifer storage

The number of days with rain in Tel Aviv is on average45 per year but only 31 days have more than 2 mm perday and therefore only a small number of days

Figure 5 Simulated volume of imported water and figures provided by the municipality from 2003 to 2007 (X-axis mmyy)

Figure 6 Total monthly wastewater production of Tel Aviv in year 2008 as estimated based on total Tel Avivrsquos share of totalDan Region wastewater production (lsquoEstimated datarsquo) and as simulated by AquaCycle

Figure 7 Tel Avivrsquos average water balance for 2003ndash2007(Stormwater flux includes the groundwater baseflow)

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generate significant runoff for stormwater harvestingAnother limiting factor in Tel Aviv is that the demandfor stormwater for irrigation is in the dry season whenthere is obviously no stormwater generation Still withthe cluster storage volumes indicated earlier (in total60000 m3 or 033 m3 per household) a reduction inwater import of 34 can be achieved Increasing totalstorage volume increases the percentage water savingbut reduces the efficiency of the tank (Figure 10) Aneconomic analysis is required to determine a feasiblevolume for the cluster stormwater tanks and this inturn determines the potential for water saving ofthis strategy Saving more than 5 by stormwaterharvesting is estimated to be very unlikely

B Rainwater harvesting

This strategy is more effective than strategy A in termsof overall water savings in the city and also moreefficient in terms of the volume of water saved per unit

rainwater tank volume (Figure 10) This difference iscaused by the higher quality of the rainwater whichallows (in this study) use for all household purposesFor a tank of 330 L per household the collectedrainwater is used for 32 and spilled from the tank for68 In strategy A the quality of the stormwater onlyallows use for toilet flushing and it is therefore mostlyspilled from the storage tanks during storm events (peryear 8 usage 92 spillage for the case with 033 m3

tank volume per household) In addition stormwaterin strategy A is in fact hardly used for irrigation sincethe storm events take place outside the irrigationseason Assuming that it is economical feasible toinstall a rainwater tank volume of about 075 m3 perhousehold then a total saving of 10 of water importsinto the city is possible Rozos et al (forthcoming)calculated that a 10 reduction of potable waterdemand in households in a Mediterranean climatewould increase the capital cost of the water supplysystem with about 40 while a 20 reduction in

Figure 8 The energy consuming components of Tel Avivrsquos water system

Figure 9 Energy use intensity of water and wastewater services by city (For Tel Aviv without energy consumption for theconveyance of effluent to irrigation areas in the Negev)Source Kenway et al (2008) SWITCH unpublished data

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demand would be achievable when accepting a 160cost increase (ie even larger storage tanks)

C Permeable pavement

The surface of Tel Aviv is for 30 permeable and 70impermeable according to the calculated and esti-mated physical characteristics of the city (Tables 3and 4) The impermeable surface consists for 33 ofroads and pavements which could be made permeableby application of permeable types of pavementsAssuming that 80 of the roads and pavements canbe made permeable then the total impermeablesurface has been reduced by 26 Simulation withthe model showed that this would result in a reductionin stormwater generation of 20 (from 177 to 141MCM per year) The reduction in stormwater genera-tion is not only due to increased infiltration becausethe model simulates infiltration to increase onlyfrom 23 to 38 MCM per year The rest of thestormwater evaporates from the soil moisture storeand overflows via pervious surface runoff into thedrainage system

The purpose of this strategy would be to increaseaquifer recharge to allow more aquifer abstractionThe extra volume of abstraction per m2 of made-permeable pavement is about 02 m3m2 per yearA financial analysis will most likely show thatthis strategy is not feasible from a financial pointof view

D Wastewater reuse at unit-block scale

The model simulated grey wastewater treatmentstorage and reuse at household scale The storage

tank volumes based on the AquaCycle optimisationroutine resulted in a 21 reduced demand forimported water (99 MCM ) and a 27 reduction inwastewater flows from the city (94 MCM) Spillagefrom the tanks was small and therefore doubling thetank volumes changed the savings to 23 and 29 onlyrespectively Benefits of this strategy are reduced totaldemand which reduces the need for seawater desalina-tion and cost savings for wastewater collection andtreatment Costs of this strategy include costs forthe household-scale treatment and reuse system andthe reduction in effluent availability for agriculturein the Negev Potential health risks from wastewaterstorage and treatment at household and from potentialcross connections in double distribution networksshould also be addressed

E Wastewater reuse at cluster scale

The model simulated grey wastewater treatment andstorage at cluster level and reuse for toilet flushingirrigation of gardens and irrigation of open publicspace The storage tank volumes based on theAquaCycle optimisation routine resulted in a 25reduced demand for imported water (115 MCM )and a 31 reduction in wastewater flows from thecity (108 MCM) Doubling the tank volumeschanged the savings to 32 and 40 respectivelyThe saving of imported water per unit volumestorage tank for the smaller (021 m3household)and larger (042 m3 per household) tanks were 300and 194 m3m3 per year respectively Comparingthese figures to stormwater strategies A and B(Figure 10) clearly shows that wastewater reuse hasmore potential to save imported water and requires

Figure 10 Potential for yearly water saving by implementation of strategies A and B (for the 2009 population and averageclimatic conditions of 1994ndash2007)

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smaller tanks Reason for this difference is thatwastewater supply to the storage tanks is much lessfluctuating than stormwater flows

36 Evaluation of strategies under scenarios till2050 ndash demand for imported water (Indicator 5)

The demand for imported water in the city under thebaseline scenario increases from 472 MCM in 2009 to759 MCM in 2050 (Figure 11) due to populationgrowth The other scenarios slightly increase thedemand for imported water (778 MCM in 2050 forthe extreme scenario) The effect of climate change issmaller than one would maybe expect because thereduction in rainfall in the wet season does not increasethe demand for irrigation water since that demand isthere only in the dry season The increase intemperature during the dry season increases the

evapotranspiration and demand for irrigation waterbut only to a limited extend

The volume of water saved by the differentstrategies is constant with time for the lsquobaselinersquo andlsquono major changersquo scenarios but is affected by thechange in precipitation and temperature in the otherscenarios The volume of water saved by the strategy B(rainwater harvesting) will be less under the latterscenarios because the rainfall is less Figure 11 alsoshows that the volume of water saved in that strategyfluctuates from year to year with the fluctuations inyearly rainfall

The timing of the implementation of the strategiescould be based on keeping the total demand forimported water under a certain level Figure 12 showshow implementation of strategies B and D partlycancels the increase in demand due to populationgrowth

Figure 12 The simulated import of fresh water into Tel Aviv until 2050 based on phased implementation of strategies B and Dunder lsquonormalrsquo and lsquoextremersquo scenarios

Figure 11 The simulated import of fresh water into Tel Aviv until 2050 based on the lsquonormalrsquo scenario and different strategiesEmpirical data for 1996ndash2006 is also shown (source TahalMunicipality of Tel Aviv)

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37 Evaluation of strategies under scenarios till2050 ndash other indicators

Energy consumption per volume of water consumedcould be reduced by various measures such asreduction of physical leakage (Colombo et al 2002)or by optimising pump technology and pumpingschedules Energy consumption of the alternativestrategies was calculated to investigate their effecton the nexus water ndash energy The energy consumptionin the whole urban water system (Table 6) per m3

of water used (imported thorn reused water) in the citywas on average 289 kWh per m3 for the period2009ndash2050 (baseline scenario) Implementation of thestrategies affected the energy consumption in differentways Strategy B with a 330-L tank per householdresults in 274 kWhm3 mainly because rainwatersystems are estimated to use 0278 KWhm3 (Kenwayet al 2008) which is less energy intensive thenimporting water Wastewater treatment and reuse atcluster scale (strategy E 210-L tank per household)reduces energy consumption to 245 kWhm3 but thesame strategy at household (strategy D 200-L tankper household in cluster 1 2 3 5 6 and 100 L incluster 4) scale increases energy consumption till 318kWhm3 This is due to the higher energy con-sumption for on-site wastewater treatment systems(4 kWhm3 Steendam 2009) than for small waste-water treatment plants (estimated as 08 kWhm3

based on a reported range of 039 to 117 kWhm3 by

Young and Koopman 1991) Therefore it seems thatstrategy D performs best for both saving water andsaving energy

Implementation of the strategies will clearly affectsome of the indicators (Table 2 indicators 5 6 7 810) while other indicators are conditions for successfulimplementation (indicators 1 2 4 6) rather thanresults and yet other indicators are not likely to beaffected (indicators 11 12 13) The effect of thestrategies on groundwater quality and receiving surfacewater quality (indicator 9) is unsure and the topic ofongoing investigations

4 Conclusions

Based on the investigation of Tel Avivrsquos urban watersystem and the simulation results of AquaCyclefollowing conclusions are drawn

The volume of water imported into the city (onaverage 47 MCM per year) and the seasonalfluctuations in the period 2003ndash2007 was accu-rately described by the AquaCycle model usingthe input files on climate physical characteristicsof the city surface and average figures fordomestic end-use categories

Evaluation of several strategies to improve thesustainability of the water system showedthat rainwater harvesting from roofs for non-

Table 6 Energy consumption inventory of Tel Avivrsquos water system

Energy consumption(KWhm3)

Proportion oftotal amount

of water Source of data

Pumping water from the Lake ofGalilee to the city

13 90 Mekorot Company

Treating water from the Lake of Galilee 0 100 Mekorot Company(negligible since supplied toconsumer without treatment)

Treating amp pumping Sea water 39 2 Mekorot CompanyPumping groundwater from local wells 0371 8 Tel Aviv MunicipalityTreating groundwater from local wells 0 8 Tel Aviv Municipality

(negligible since supplied toconsumer without treatment)

Pumping for distributing water ndash North area 0103 135 Tel Aviv MunicipalityPumping for distributing water ndash South area 0077 72 Tel Aviv MunicipalityHeating water at household 407 27 EstimationWastewater collection 0111 100 Tel Aviv MunicipalityWastewater treatment 0425 100 Mekorot CompanyPumping treated wastewater for irrigation 145 100 Mekorot CompanyPumping stormwater 0 100 Tel Aviv Municipality

(negligible since dischargeddirectly to the Sea by gravity)

Total ( including heating water at household) 1427Total (not including household heating water ) 328

It was assumed that all water supplied by Mekorot to the city was taken from the Lake of Galilee rather than from groundwater pumpingstations closer to the city (such as Rosh HaAyin)

Based on 1 m3 supplied collected treated and reused

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potable reuse in households is more promisingthan stormwater collection and reuse at clusterscale Assuming that it is feasible to install arainwater tank volume of about 075 m3 perhousehold then a total saving of 10 of waterimports into the city is possible

The overall water mass balance for the cityshowed that this rainwater harvesting strategywould reduce the amount of stormwater thatleaves the city per year from 22 MCM toabout 17 MCM which shows that othertechnologies or approaches are necessary ifone would like to make full beneficial use ofthis resource

Increasing rainwater infiltration for aquiferrecharge is most likely not financially sustainablesince the extra volume of recharge to allow moreaquifer abstraction is only 02 m3year per m2 ofmade-permeable pavement

The largest saving of water imports could beachieved by wastewater reuse for urban non-potable uses Wastewater collection storage(042 m3 per household) treatment and reuse atcluster scale is simulated to result in a 32 and40 reduction in water imports and wastewaterflows respectively

The most important factor of future scenariosfor water demand is population growth Effectsof climate change (reduced rainfall to a max-imum of 30 and increase in temperature to amaximum of 258C) on imported water weremuch smaller not more than 25 increase inthe extreme scenario This is in agreement withRozos et al (forthcoming) who have estimatedfor a Mediterranean climate an increase between0 and 4 depending on the capacity of therainwater harvesting scheme

Energy consumption in the urban water systemwas calculated as 289 kWh per m3 of volume ofwater used (import thorn reuse) in the city forthe period 2009ndash2050 Implementation of thestrategies affects the energy consumption indifferent ways Rainwater harvesting has somepotential to reduce energy consumption (to 274kWh per m3) but the best strategy in thisrespect is wastewater treatment and reuse atcluster scale (245 kWh per m3) The samestrategy at household scale causes an increasein energy consumption (318 kWh per m3)

The results of the model and the scenarioplanning study can be used to score a numberof the suggested sustainability indicators for theurban water system of Tel Aviv and as such canbe used by the multidisciplinary Water Club tosteer the city towards sustainability

Acknowledgements

The authors would like to thank the Dutch governmentfor its support through the NPT programme andthe European Commission for its support through theSWITCH project (FP6 Global Change and Ecosystems018530)

References

Butterworth JA Sutherland A Manning N Darteh BDziegielewska-Geitz M Eckart J Batchelor CMoriarty P Schouten T Da Silva C Verhagen Jand Bury PJ 2008 Building more effective partnershipsfor innovation in urban water management In Interna-tional Conference on Water and Urban DevelopmentParadigms Towards an integration of engineering designand management approaches 15ndash19 September 2008Katholieke Universiteit Leuven Belgium

Cities Alliance 2006 Guide to City Development StrategiesImproving urban performance Washington DC USApp 92

Colombo AF and Karney BW 2002 Energy and costs ofleaky pipes Toward comprehensive picture ASCEJournal of Water Resources Planning and Management128 (6) 441ndash450

ECAampD (European Climate Assessment amp Dataset Project)2008 Data records httpecaknminl [AccessedApril 2010]

Israel Ministry of Environmental Protection 2008 Israelrsquosadaption to climate change ndash Impacts and recommenda-tion httpwwwsvivagovil [Accessed April 2010]

Karka P Manoli E Lekkas DF and AssimacopoulosD 2007 A case study on integrated urban watermodelling using aquacyle In Proceedings of the 10thInternational Conference on Environmental Science ampTechnology Kos Island Greece 5ndash7 September 2007

Kenway SJ Priestley A Cook S Seo S Inman MGregory A and Hall M 2008 Energy use in theprovision and consumption of urban water in Australiaamp New Zealand Water for a Healthy country Flagshipreport series ISSN 1835ndash095X Water Service Associa-tion of Australia

Lundin M 2003 Indicators for measuring the sustainabilityof urban water system ndash A life cycle approach PhDdissertation Chalmers University of Technology

Makropoulos CK Memon FA Shirley-Smith C andButler D 2008a Futures An exploration of scenariosfor sustainable urban water management Water Policy10 345ndash373

Makropoulos CK Natsis K Liu S Mittas K andButler D 2008b Decision support for sustainableoption selection in integrated urban water managementEnvironmental Modelling amp Software 23 (12) 1448ndash1460

Mitchell V 2005 AquaCycle user guide A daily urban waterbalance model Australia Monash University Press

Mitchell V 2006 Applying integrated urban water manage-ment concepts A review of Australian experienceEnvironmental Management 37 (5) 589ndash605

Mitchell V Mein RG and McMahon TA 2001Modelling the urban water cycle Environmental Model-ling amp Software 16 615ndash629

Municipality of Tel Aviv 2006 City ndash The Strategic plan forTel Aviv Yafo Strategic Planning Unit Tel AvivMunicipality Israel

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calculated based on the total area of a cluster minusthe area of roads and public open spaces The averagearea of one unit-block was obtained from the total areaof unit-blocks and the number of unit-blocks withinthe cluster Physical characteristics of a representativeapartment block were estimated by observation basedon satellite images and site visits It was estimated thatthe areas of roof garden and pavement per apartmentblock are 70 15 and 15 respectively The areas wereproportionally allocated to the apartments in the blockand therefore the percentages are also valid for theunit-blocks in the model

26 AquaCycle outputs and energy calculations

The output of the model is a water balance with dailyvalues for precipitation piped water supply evapo-transpiration stormwater drainage and wastewatercollection Monthly or yearly average values can becalculated for the catchment cluster or unit-blockscale The mass balance for the catchment scale wasused to calculate the total energy consumption of thesystem All components of the water system thatconsume energy were identified by interviewing staff ofTel Aviv municipality and the Mekorot company anddata on energy consumption (mostly in kWhm3) wereobtained

27 Formulation of scenarios

Scenarios were not formulated to predict the futurebut were used by the LA as tools for thinking about

possible futures and to evaluate the impact ofdecisions taken today on these futures Commonelements in the scenarios were based on regulatorysocial economic environmental and technical aspects(Makropoulos et al 2008a) but not all of theseelements can be modelled quantitatively In thiswork four quantitative scenarios were formulatedfor Tel Aviv until the year 2050 including fourfactors precipitation temperature population growthand urbanisation all of which can be simulated byAquaCycle simulation (see Table 1) All of thesefactors impact directly or indirectly on Tel Avivrsquosurban water system via the effects on water demandwater resources water infrastructure and urban sur-face permeability The baseline scenario describes thecurrent situation of the city The lsquonormalrsquo scenario isbased on estimations on climate change by IsraelMinistry of Environmental Protection (2008) Data onhistorical population growth rate (22) was obtainedfrom Tel Aviv Municipality The scenarios assumedthe same growth rate to continue until 2050 whichwould only be possible by densification and morehigh-rise buildings in the city In all scenariosdensification leads to a reduction in (permeable) publicopen space of 20

28 Formulation of strategies

The LA developed strategies to achieve the visiongiven the possible future scenarios through groupdiscussions and by one-on-one interviews Onlystrategies that could be simulated by AquaCycle arepresented here The strategies are

A Stormwater use and temporary aquifer storage

Measures for stormwater use and aquifer infiltrationprojects were simulated for each cluster The storm-water from the unit-blocks and from the roads drainedinto a stormwater storage tank in each cluster and wasreused for toilet flushing garden and public spaceirrigation Excess stormwater was infiltrated into theaquifer The stormwater surface storage volumesinitially used were cluster 1 15000 m3 cluster 25000 m3 cluster 3 15000 m3 cluster 4 15000 m3cluster 5 5000 m3 cluster 6 5000 m3 (based on theoptimisation routine of AquaCycle) A 10000 m3 ofaquifer storage was applied for each cluster The effectof increasing and decreasing these volumes wasinvestigated as well

B Rainwater harvesting

A rainwater tank of various sizes was applied atevery household in all clusters of the city Rain

Figure 4 Clusters defined for the Tel Aviv catchment(Numbers 1ndash6) and Tel Avivrsquos neighbouring municipalities

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water was used in the kitchen for laundry inthe bathroom for toilet flushing and for gardenirrigation

C Permeable pavement

Pavements in unit-block gardens and for roads werereplaced by permeable pavements simulated in Aqua-Cycle by increasing the garden and open space area inthe city

D Wastewater reuse at unit-block scale

Decentralised wastewater treatment units were appliedat every household in the city Wastewater fromkitchen bathroom and laundry was treated and reusedfor toilet flushing and garden irrigation It wasassumed that no water was lost in the treatmentprocess The storage volume for treated wastewater atevery household in each cluster was identified accord-ing to the optimisation results of AquaCycle (200 L ofwastewater storage per household in cluster 1 2 3 56 and 100 L of wastewater storage in cluster 4)

E Wastewater reuse at cluster scale

Wastewater treatment units were applied for eachcluster Household wastewater draining to a clusterwastewater storage tank was treated stored andsupplied for toilet flushing and garden irrigation forhouseholds and for open space irrigation It wasassumed that no water was lost in the treatmentprocess The treated wastewater storage volumes werecluster 1 7900 m3 cluster 2 4700 m3 cluster 38300 m3 cluster 4 1300 m3 cluster 5 9100 m3cluster 6 7200 m3 (based on the optimisation routineof AquaCycle)

29 Evaluation of strategies

As mentioned above the LA developed a vision for asustainable urban water system for the city This visionwas translated into tangible objectives the achieve-ment of which can be measured by sustainabilityindicators The score for these indicators were used toevaluate the strategies rather than by a thoroughengineering and economic feasibility study Some ofthe indicators could be evaluated in a quantitative wayusing the AquaCycle outputs others were evaluatedqualitatively

3 Results and discussion

31 Sustainability objectives and indicators

Based on interviews and general investigations it wasfound that the urban water system of Tel Aviv istypical for an advanced developed country but alsocharacterised by a number of un-sustainability factorswhich need improvement With regard to planning ofthe whole system it was noticed that lsquowater manage-mentrsquo is not addressed in the Strategic Plan of the city(Municipality of Tel Aviv 2006) and water indicatorsare therefore also not included in the set of indicatorsthat is used to monitor the development of the cityThis is somewhat surprising since the domestic waterconsumption in the city is higher than the amount thatcan be sustained from renewable water sources Thewater supply system is also threatened by insufficientmaintenance of the distribution system which causesbio-film growth and microbial pollution which in turnmay cause a higher chlorine demand One of theunderlying causes of the poor maintenance is lack ofsuitable financial resources for local government tomaintain the drinking water quality The same reasonsalso result in frequent leakages from the sewer system

Table 1 Formulated scenarios and factors until the year 2050

FactorPrecipitationdecrease

Temperatureincrease

Populationgrowth rate Urbanisation

Baseline scenario ndash ndash 22lsquoNo major changersquo scenario ndash ndash 22 20 of public open space is replaced

by residential area (10 in 2022 andanother 10 in 2046) road area isnot changed

lsquoNormalrsquo scenario 20 158C 22 20 of public open space is replacedby residential area (10 in 2022 andanother 10 in 2046) road area isnot changed

lsquoExtremersquo scenario 30 258C 22 20 of public open space is replacedby residential area (10 in 2022 andanother 10 in 2046) road area isnot changed

From 2023 onwards

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which causes severe pollution of the local aquiferwhich is one of the drinking water sources for the cityBasically all municipal wastewater is collected andtreated to a tertiary level but it is not utilised foragricultural irrigation within the region but in theNegev Urban parks in Tel Aviv are still irrigated withfresh water Stormwater is collected in a separatedrainage system but discharged directly to the seawithout any treatment There is no monitoring systemor research to evaluate the amount of stormwatergenerated in the city and its quality It is likely that TelAviv is overlooking the potential to use this nonconventional water resource The capacity of thedrainage system is not sufficient to prevent occasionalflooding Finally the un-sustainability of the systembecomes clear from the significant amount of energyused to transport fresh water over long distances anduphill (from the Sea of Galilee) to treat wastewater inan energy intensive system and finally to pump effluentto irrigation fields in the south of the country Thecommissioning of desalination plants will only increasethe energy consumption in the system

Based on this assessment the LA formulated aVision for sustainable urban water management in TelAviv lsquoTel Avivrsquos water system management will beestablished based on sustainability indicators andapply an efficient and integrated water managementto meet the water demand of citizens and for otherapplications with sufficient qualities and reasonableprices while the natural status of water resources isassuredrsquo The vision was translated into a set oftangible objectives and related indicators as shownin Table 2

32 Model calibration and simulation of wastewateroutput

The characteristics of the modelled clusters and therepresentative unit-block are outlined in Table 3 and 4The meteorological data the indoor water use profileand physical site characteristics were used as inputsfor the model The default calibration parameters(Table 5) initially were used and the model output interms of lsquoimported waterrsquo was compared with themunicipalities measured data on total water distrib-uted to the consumers The average amount oflsquoimported waterrsquo simulated by the model was about10 lower than the total water consumption Thelsquotrigger to irrigatersquo is the fraction of the optimal soilmoisture for plant growth which is still acceptable tothe user This trigger for private gardens and publicopen space was adjusted to 062 and as a result theaverage lsquoimported waterrsquo simulated by the model thenwas exactly the average volume of water distributed tothe consumers (Figure 5)

The monthly water consumption in the city isabout 40 higher in the summer irrigation seasonthan in the winter season The seasonal fluctuationcould be described well by the model throughirrigation of private gardens and public open spaceIt is likely that also the indoor water use is higher insummer but it is not possible in AquaCycle to changethe household indoor water consumption between theseasons Variation in imported water based on thefigures provided by the municipality (Figure 5) isrelatively large between some of the summer monthsespecially in 2004 and 2007 The reason for these largerfluctuations is unknown since the differences intemperature and potential evapotranspiration do notseem to explain such large fluctuations The model istherefore also not able to describe well these short-termfluctuations

Further calibration of the model was attemptedon observed wastewater flows from the wider TelAviv area (the Dan District) Unfortunately thewastewater flow from Tel Aviv is not measuredseparately from the wastewater flow from surround-ing municipalities It was therefore assumed that theamount of wastewater production per capita per yearin the various municipalities in the Dan District is thesame Therefore based on the population of TelAviv the amount of wastewater generated from TelAviv is estimated as 326 of total wastewaterproduction of the Dan District The wastewater flowssimulated by AquaCycle in the dry season (AprilndashOctober) were 18 lower than the flows based onmeasurements and the above described calculation(Figure 6) The simulated values may actually becloser to reality since the simulated values are90 of the indoor water consumption (about 31MCMmonth Figure 5) whereas the measured value(adjusted for population) is more than the actualindoor water consumption The higher flows inJanuary March and December are caused by wrongconnections between the stormwater drainage andfoul sewerage system The observed increase due tostormwater infiltration could be used to adjust thecalibration parameter lsquo of surface runoff as inflowrsquo(Table 5) The default value is 3 but a better fitwas achieved by using 7 This percentage is similarto the estimate of infiltration by Mekorot theoperator of the treatment plant (Aharoni personalcommunication)

33 The water balance of the system

The calibrated model was used to prepare the averageannual water balance for the city for the years2003ndash2007 (Figure 7) The water balance can be usedfor a fundamental evaluation of the sustainability of

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Table

2

Specificobjectives

andsustainabilityindicators

fortheurbanwatersystem

ofTel

Aviv

Specificobjective

Indicator

Unit

WaterPolicy

1TA

willraiseawarenessamongitscitizensabout

lsquowaterandsustainabilityrsquoandwillinvolvethe

publicin

decisionmaking

Thenumber

ofcitizensthatwillparticipate

inconsultativemeetings

Number

ofcitizensper

year

2TA

willmanageitsurbanwatersystem

inan

integratedwayintegratingaspects

ofwater

supplystorm

wateramp

wastew

atermanagem

ent

Theproductionofanintegratedurbanwater

managem

entplanforthecity

at2-yearintervals

Tim

elyproductionofintegratedplan

3A

setofsustainabilityindicators

willbeaccepted

andtheseindicators

willbeusedfordecision

makingandplanning

Referencesin

municipalplanningpolicy

documents

andgovernmentdecisionsto

the

sustainabilityindicators

Number

ofdocuments

withreferences

4TA

willstrengthen

thescientificbasisofitsdecision

makingconcerningthemanagem

entofitsUrban

WaterSystem

Thenumber

ofmunicipality

staffthatisusing

resultsfrom

scientificresearchin

theirdailywork

Number

ofstaff

WaterDem

andManagem

ent

5Thetotaldem

andin

TA

forfreshwateristo

be

reducedby10

by2050

Thereductionin

freshwatervolumeim

ported

tothecitycomparedto

the2009value

m3yearor

reduction

6Rainwaterandstorm

waterharvestingfor

non-potable

reuse

inthedomesticsectorwillbe

investigatedandapplied

ifoverallsustainability

ofthesystem

isincreased

Availabilityofastudyonrainwaterandor

storm

waterharvestingin

TA

Availabilityofstudy

Thenumber

ofhouseholdscollectingrainwater

Number

ofhouseholds

Thevolumeofrainwaterandorstorm

water

collectedandusedfornon-potable

use

m3year

7TA

willphase

outtheirrigationofurbanparks

withfreshwaterandwillonly

use

recycled

wastew

ater

forthispurpose

Thevolumeoffreshwaterorrecycled

wastew

aterusedforpark

irrigation

m3year

Percentageoftotalareairrigatedbyfreshwater

8

TA

willinfiltrate

storm

watergeneratedin

itsareainto

theaquiferherebyreducingthespillofwaterto

thesea

reducingthehydraulicloadto

theWWTPand

contributingto

aquifer

replenishmentTA

willtakecare

thatthestorm

waterisnotpolluted

Thepercentageofstorm

waterthatisinfiltrated

into

theaquifer

EnvironmentalProtection

9TA

willrestore

andprotect

itssurface

water

(YarkonRiver)

Thewaterquality

oftheYarkonriver

expressed

incommonly

usedwaterquality

parameters

(BODCOD)

various

10

TA

willminim

izetheenergyconsumptionin

theurban

watersystem

Thetotalquantity

ofenergyfrom

non-renew

able

sources

usedto

operate

theurbanwatersystem

includingwaterheatingin

thehouseholds

kWhyear

Socio-economy

11

TA

willsupply

waterofgoodquality

toitscitizens

atreasonable

price

insufficientqualities

ThefractionofsamplesanalyzedbytheMinistry

ofHealththatdoes

notsatisfythehealthcriteria

Thefrequency

ofsupply

interruptions

Downtimeper

year

12

TA

willensure

equityin

theaccessto

wateraswell

asto

irrigatedgreen

areas

Thespatialdistributionofwaterquality

and

frequency

ofserviceinterruptionsin

thecity

Mapwithwaterquality

andservice

interruptionfrequency

Thegreen

areaavailable

per

personandits

spatialdistribution

Mapwithm

2green

areaper

capita

13

TA

willreduce

therisk

offloodingin

vulnerable

arearsquos

toafrequency

thatisacceptable

toallstakeholderseven

under

future

clim

ate

changescenarios

Thenumber

ofpeople

affectedbyfloodingper

year

Number

ofpeople

per

year

Theeconomic

damagecausedbyflooding

USDyear

110 TTH Duong et al

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the system The natural precipitation would not besufficient to satisfy current demand therefore largewater imports are required About 7 of the totalsystem inputs infiltrate into the groundwater andare in principle available for recovery from theaquifer In 2008 the municipality pumped slightlymore than 4 MCM from the aquifer therefore theTel Aviv urban area does not directly contribute toaquifer depletion The largest outflow from the city isthe wastewater flow which is treated and reused in theNegev The largest flux that is not beneficially used isthe stormwater flow If all stormwater would becaptured and used for urban purposes then about50 of the urban demand could be met by reclaimedstormwater

34 Results of the energy balance

The water balance for the city was used to calculatethe energy consumption in the urban water system(Figure 8) For each point of energy consumption inthe system the specific energy consumption in kWhm3

was determined as well as the proportion of the totalflow passing through that specific pathway Thus thetotal energy consumption in the system was calculatedas 328 kWhm3 This figure does not include energyconsumption for water heating in the householdThe largest energy consumption in the water systemitself is due to the long distance from the Lake ofGalilee seawater desalination wastewater treatmentand conveyance of effluent to the Negev The current

Table 3 Overview of cluster characteristics

Cluster 1 2 3 4 5 6

Population 80007 49095 84834 14384 91656 74964Total area (ha) 7451 6477 1459 6590 6470 9846Roads ( ha) 1135 976 1579 248 1180 1588Public open space (ha) 1490 648 2927 3927 647 646Unit-blocks (ha) 4825 4854 10084 2415 4643 7612

Table 4 Overview of unit-block characteristics

ClusterNumber ofunit-blocks

Averageoccupancy

Average areaof a unit-block (m2)

Area ofroof m2 (70)

Area ofgarden m2 (15)

Area ofpavement m2 (15)

1 36367 22 1327 929 199 1992 22316 22 2175 1523 326 3263 38561 22 2615 1831 392 3924 6538 22 3694 2586 554 5545 41662 22 1115 780 167 1676 34074 22 2234 1564 335 335

Table 5 Parameters used for the model calibration

Output Calibration parameter Default After calibration Units

Stormwater Percentage area of store 1 22 Pervious storage 1 capacity 32 mmPervious storage 2 capacity 240 mmRoof area maximum initial loss 0 mmEffective roof area 100 Paved area maximum initial loss 0 mmEffective paved area 100 Road area maximum initial loss 0 mmEffective road area 100 Base flow index 055 RatioBase flow recession constant 00025 Ratio

Wastewater Infiltration index 0095 RatioInfiltration store recession constant 012 Ratio of surface runoff as inflow 3 7

Imported water Garden trigger to irrigate 05 062 RatioPublic open space trigger to irrigate 042 062 Ratio

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contribution of desalination is small because only asmall fraction of the water use originates in desalina-tion plants but this is likely to increase in the futureNote that the specific energy consumption for desali-nation is several times the sum of all specific energyconsumption in the rest of the system

Figure 9 compares the energy consumption in TelAviv with some Australian cities (Kenway et al 2008)and with Zaragosa in Spain (SWITCH 2008 unpub-lished data) The energy costs in those cities for watertreatment and water pumping are highly variabledepending on quality and distance of the waterresource The energy consumption for wastewatertreatment and wastewater pumping (not includingconveyance to the Negev) is in the same range asobserved for the other cities

35 Evaluation of strategies ndash for the 2009 populationand average climatic conditions of 1994ndash2007

A Stormwater use and temporary aquifer storage

The number of days with rain in Tel Aviv is on average45 per year but only 31 days have more than 2 mm perday and therefore only a small number of days

Figure 5 Simulated volume of imported water and figures provided by the municipality from 2003 to 2007 (X-axis mmyy)

Figure 6 Total monthly wastewater production of Tel Aviv in year 2008 as estimated based on total Tel Avivrsquos share of totalDan Region wastewater production (lsquoEstimated datarsquo) and as simulated by AquaCycle

Figure 7 Tel Avivrsquos average water balance for 2003ndash2007(Stormwater flux includes the groundwater baseflow)

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generate significant runoff for stormwater harvestingAnother limiting factor in Tel Aviv is that the demandfor stormwater for irrigation is in the dry season whenthere is obviously no stormwater generation Still withthe cluster storage volumes indicated earlier (in total60000 m3 or 033 m3 per household) a reduction inwater import of 34 can be achieved Increasing totalstorage volume increases the percentage water savingbut reduces the efficiency of the tank (Figure 10) Aneconomic analysis is required to determine a feasiblevolume for the cluster stormwater tanks and this inturn determines the potential for water saving ofthis strategy Saving more than 5 by stormwaterharvesting is estimated to be very unlikely

B Rainwater harvesting

This strategy is more effective than strategy A in termsof overall water savings in the city and also moreefficient in terms of the volume of water saved per unit

rainwater tank volume (Figure 10) This difference iscaused by the higher quality of the rainwater whichallows (in this study) use for all household purposesFor a tank of 330 L per household the collectedrainwater is used for 32 and spilled from the tank for68 In strategy A the quality of the stormwater onlyallows use for toilet flushing and it is therefore mostlyspilled from the storage tanks during storm events (peryear 8 usage 92 spillage for the case with 033 m3

tank volume per household) In addition stormwaterin strategy A is in fact hardly used for irrigation sincethe storm events take place outside the irrigationseason Assuming that it is economical feasible toinstall a rainwater tank volume of about 075 m3 perhousehold then a total saving of 10 of water importsinto the city is possible Rozos et al (forthcoming)calculated that a 10 reduction of potable waterdemand in households in a Mediterranean climatewould increase the capital cost of the water supplysystem with about 40 while a 20 reduction in

Figure 8 The energy consuming components of Tel Avivrsquos water system

Figure 9 Energy use intensity of water and wastewater services by city (For Tel Aviv without energy consumption for theconveyance of effluent to irrigation areas in the Negev)Source Kenway et al (2008) SWITCH unpublished data

Urban Water Journal 113

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demand would be achievable when accepting a 160cost increase (ie even larger storage tanks)

C Permeable pavement

The surface of Tel Aviv is for 30 permeable and 70impermeable according to the calculated and esti-mated physical characteristics of the city (Tables 3and 4) The impermeable surface consists for 33 ofroads and pavements which could be made permeableby application of permeable types of pavementsAssuming that 80 of the roads and pavements canbe made permeable then the total impermeablesurface has been reduced by 26 Simulation withthe model showed that this would result in a reductionin stormwater generation of 20 (from 177 to 141MCM per year) The reduction in stormwater genera-tion is not only due to increased infiltration becausethe model simulates infiltration to increase onlyfrom 23 to 38 MCM per year The rest of thestormwater evaporates from the soil moisture storeand overflows via pervious surface runoff into thedrainage system

The purpose of this strategy would be to increaseaquifer recharge to allow more aquifer abstractionThe extra volume of abstraction per m2 of made-permeable pavement is about 02 m3m2 per yearA financial analysis will most likely show thatthis strategy is not feasible from a financial pointof view

D Wastewater reuse at unit-block scale

The model simulated grey wastewater treatmentstorage and reuse at household scale The storage

tank volumes based on the AquaCycle optimisationroutine resulted in a 21 reduced demand forimported water (99 MCM ) and a 27 reduction inwastewater flows from the city (94 MCM) Spillagefrom the tanks was small and therefore doubling thetank volumes changed the savings to 23 and 29 onlyrespectively Benefits of this strategy are reduced totaldemand which reduces the need for seawater desalina-tion and cost savings for wastewater collection andtreatment Costs of this strategy include costs forthe household-scale treatment and reuse system andthe reduction in effluent availability for agriculturein the Negev Potential health risks from wastewaterstorage and treatment at household and from potentialcross connections in double distribution networksshould also be addressed

E Wastewater reuse at cluster scale

The model simulated grey wastewater treatment andstorage at cluster level and reuse for toilet flushingirrigation of gardens and irrigation of open publicspace The storage tank volumes based on theAquaCycle optimisation routine resulted in a 25reduced demand for imported water (115 MCM )and a 31 reduction in wastewater flows from thecity (108 MCM) Doubling the tank volumeschanged the savings to 32 and 40 respectivelyThe saving of imported water per unit volumestorage tank for the smaller (021 m3household)and larger (042 m3 per household) tanks were 300and 194 m3m3 per year respectively Comparingthese figures to stormwater strategies A and B(Figure 10) clearly shows that wastewater reuse hasmore potential to save imported water and requires

Figure 10 Potential for yearly water saving by implementation of strategies A and B (for the 2009 population and averageclimatic conditions of 1994ndash2007)

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smaller tanks Reason for this difference is thatwastewater supply to the storage tanks is much lessfluctuating than stormwater flows

36 Evaluation of strategies under scenarios till2050 ndash demand for imported water (Indicator 5)

The demand for imported water in the city under thebaseline scenario increases from 472 MCM in 2009 to759 MCM in 2050 (Figure 11) due to populationgrowth The other scenarios slightly increase thedemand for imported water (778 MCM in 2050 forthe extreme scenario) The effect of climate change issmaller than one would maybe expect because thereduction in rainfall in the wet season does not increasethe demand for irrigation water since that demand isthere only in the dry season The increase intemperature during the dry season increases the

evapotranspiration and demand for irrigation waterbut only to a limited extend

The volume of water saved by the differentstrategies is constant with time for the lsquobaselinersquo andlsquono major changersquo scenarios but is affected by thechange in precipitation and temperature in the otherscenarios The volume of water saved by the strategy B(rainwater harvesting) will be less under the latterscenarios because the rainfall is less Figure 11 alsoshows that the volume of water saved in that strategyfluctuates from year to year with the fluctuations inyearly rainfall

The timing of the implementation of the strategiescould be based on keeping the total demand forimported water under a certain level Figure 12 showshow implementation of strategies B and D partlycancels the increase in demand due to populationgrowth

Figure 12 The simulated import of fresh water into Tel Aviv until 2050 based on phased implementation of strategies B and Dunder lsquonormalrsquo and lsquoextremersquo scenarios

Figure 11 The simulated import of fresh water into Tel Aviv until 2050 based on the lsquonormalrsquo scenario and different strategiesEmpirical data for 1996ndash2006 is also shown (source TahalMunicipality of Tel Aviv)

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37 Evaluation of strategies under scenarios till2050 ndash other indicators

Energy consumption per volume of water consumedcould be reduced by various measures such asreduction of physical leakage (Colombo et al 2002)or by optimising pump technology and pumpingschedules Energy consumption of the alternativestrategies was calculated to investigate their effecton the nexus water ndash energy The energy consumptionin the whole urban water system (Table 6) per m3

of water used (imported thorn reused water) in the citywas on average 289 kWh per m3 for the period2009ndash2050 (baseline scenario) Implementation of thestrategies affected the energy consumption in differentways Strategy B with a 330-L tank per householdresults in 274 kWhm3 mainly because rainwatersystems are estimated to use 0278 KWhm3 (Kenwayet al 2008) which is less energy intensive thenimporting water Wastewater treatment and reuse atcluster scale (strategy E 210-L tank per household)reduces energy consumption to 245 kWhm3 but thesame strategy at household (strategy D 200-L tankper household in cluster 1 2 3 5 6 and 100 L incluster 4) scale increases energy consumption till 318kWhm3 This is due to the higher energy con-sumption for on-site wastewater treatment systems(4 kWhm3 Steendam 2009) than for small waste-water treatment plants (estimated as 08 kWhm3

based on a reported range of 039 to 117 kWhm3 by

Young and Koopman 1991) Therefore it seems thatstrategy D performs best for both saving water andsaving energy

Implementation of the strategies will clearly affectsome of the indicators (Table 2 indicators 5 6 7 810) while other indicators are conditions for successfulimplementation (indicators 1 2 4 6) rather thanresults and yet other indicators are not likely to beaffected (indicators 11 12 13) The effect of thestrategies on groundwater quality and receiving surfacewater quality (indicator 9) is unsure and the topic ofongoing investigations

4 Conclusions

Based on the investigation of Tel Avivrsquos urban watersystem and the simulation results of AquaCyclefollowing conclusions are drawn

The volume of water imported into the city (onaverage 47 MCM per year) and the seasonalfluctuations in the period 2003ndash2007 was accu-rately described by the AquaCycle model usingthe input files on climate physical characteristicsof the city surface and average figures fordomestic end-use categories

Evaluation of several strategies to improve thesustainability of the water system showedthat rainwater harvesting from roofs for non-

Table 6 Energy consumption inventory of Tel Avivrsquos water system

Energy consumption(KWhm3)

Proportion oftotal amount

of water Source of data

Pumping water from the Lake ofGalilee to the city

13 90 Mekorot Company

Treating water from the Lake of Galilee 0 100 Mekorot Company(negligible since supplied toconsumer without treatment)

Treating amp pumping Sea water 39 2 Mekorot CompanyPumping groundwater from local wells 0371 8 Tel Aviv MunicipalityTreating groundwater from local wells 0 8 Tel Aviv Municipality

(negligible since supplied toconsumer without treatment)

Pumping for distributing water ndash North area 0103 135 Tel Aviv MunicipalityPumping for distributing water ndash South area 0077 72 Tel Aviv MunicipalityHeating water at household 407 27 EstimationWastewater collection 0111 100 Tel Aviv MunicipalityWastewater treatment 0425 100 Mekorot CompanyPumping treated wastewater for irrigation 145 100 Mekorot CompanyPumping stormwater 0 100 Tel Aviv Municipality

(negligible since dischargeddirectly to the Sea by gravity)

Total ( including heating water at household) 1427Total (not including household heating water ) 328

It was assumed that all water supplied by Mekorot to the city was taken from the Lake of Galilee rather than from groundwater pumpingstations closer to the city (such as Rosh HaAyin)

Based on 1 m3 supplied collected treated and reused

116 TTH Duong et al

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potable reuse in households is more promisingthan stormwater collection and reuse at clusterscale Assuming that it is feasible to install arainwater tank volume of about 075 m3 perhousehold then a total saving of 10 of waterimports into the city is possible

The overall water mass balance for the cityshowed that this rainwater harvesting strategywould reduce the amount of stormwater thatleaves the city per year from 22 MCM toabout 17 MCM which shows that othertechnologies or approaches are necessary ifone would like to make full beneficial use ofthis resource

Increasing rainwater infiltration for aquiferrecharge is most likely not financially sustainablesince the extra volume of recharge to allow moreaquifer abstraction is only 02 m3year per m2 ofmade-permeable pavement

The largest saving of water imports could beachieved by wastewater reuse for urban non-potable uses Wastewater collection storage(042 m3 per household) treatment and reuse atcluster scale is simulated to result in a 32 and40 reduction in water imports and wastewaterflows respectively

The most important factor of future scenariosfor water demand is population growth Effectsof climate change (reduced rainfall to a max-imum of 30 and increase in temperature to amaximum of 258C) on imported water weremuch smaller not more than 25 increase inthe extreme scenario This is in agreement withRozos et al (forthcoming) who have estimatedfor a Mediterranean climate an increase between0 and 4 depending on the capacity of therainwater harvesting scheme

Energy consumption in the urban water systemwas calculated as 289 kWh per m3 of volume ofwater used (import thorn reuse) in the city forthe period 2009ndash2050 Implementation of thestrategies affects the energy consumption indifferent ways Rainwater harvesting has somepotential to reduce energy consumption (to 274kWh per m3) but the best strategy in thisrespect is wastewater treatment and reuse atcluster scale (245 kWh per m3) The samestrategy at household scale causes an increasein energy consumption (318 kWh per m3)

The results of the model and the scenarioplanning study can be used to score a numberof the suggested sustainability indicators for theurban water system of Tel Aviv and as such canbe used by the multidisciplinary Water Club tosteer the city towards sustainability

Acknowledgements

The authors would like to thank the Dutch governmentfor its support through the NPT programme andthe European Commission for its support through theSWITCH project (FP6 Global Change and Ecosystems018530)

References

Butterworth JA Sutherland A Manning N Darteh BDziegielewska-Geitz M Eckart J Batchelor CMoriarty P Schouten T Da Silva C Verhagen Jand Bury PJ 2008 Building more effective partnershipsfor innovation in urban water management In Interna-tional Conference on Water and Urban DevelopmentParadigms Towards an integration of engineering designand management approaches 15ndash19 September 2008Katholieke Universiteit Leuven Belgium

Cities Alliance 2006 Guide to City Development StrategiesImproving urban performance Washington DC USApp 92

Colombo AF and Karney BW 2002 Energy and costs ofleaky pipes Toward comprehensive picture ASCEJournal of Water Resources Planning and Management128 (6) 441ndash450

ECAampD (European Climate Assessment amp Dataset Project)2008 Data records httpecaknminl [AccessedApril 2010]

Israel Ministry of Environmental Protection 2008 Israelrsquosadaption to climate change ndash Impacts and recommenda-tion httpwwwsvivagovil [Accessed April 2010]

Karka P Manoli E Lekkas DF and AssimacopoulosD 2007 A case study on integrated urban watermodelling using aquacyle In Proceedings of the 10thInternational Conference on Environmental Science ampTechnology Kos Island Greece 5ndash7 September 2007

Kenway SJ Priestley A Cook S Seo S Inman MGregory A and Hall M 2008 Energy use in theprovision and consumption of urban water in Australiaamp New Zealand Water for a Healthy country Flagshipreport series ISSN 1835ndash095X Water Service Associa-tion of Australia

Lundin M 2003 Indicators for measuring the sustainabilityof urban water system ndash A life cycle approach PhDdissertation Chalmers University of Technology

Makropoulos CK Memon FA Shirley-Smith C andButler D 2008a Futures An exploration of scenariosfor sustainable urban water management Water Policy10 345ndash373

Makropoulos CK Natsis K Liu S Mittas K andButler D 2008b Decision support for sustainableoption selection in integrated urban water managementEnvironmental Modelling amp Software 23 (12) 1448ndash1460

Mitchell V 2005 AquaCycle user guide A daily urban waterbalance model Australia Monash University Press

Mitchell V 2006 Applying integrated urban water manage-ment concepts A review of Australian experienceEnvironmental Management 37 (5) 589ndash605

Mitchell V Mein RG and McMahon TA 2001Modelling the urban water cycle Environmental Model-ling amp Software 16 615ndash629

Municipality of Tel Aviv 2006 City ndash The Strategic plan forTel Aviv Yafo Strategic Planning Unit Tel AvivMunicipality Israel

Urban Water Journal 117

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ober

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water was used in the kitchen for laundry inthe bathroom for toilet flushing and for gardenirrigation

C Permeable pavement

Pavements in unit-block gardens and for roads werereplaced by permeable pavements simulated in Aqua-Cycle by increasing the garden and open space area inthe city

D Wastewater reuse at unit-block scale

Decentralised wastewater treatment units were appliedat every household in the city Wastewater fromkitchen bathroom and laundry was treated and reusedfor toilet flushing and garden irrigation It wasassumed that no water was lost in the treatmentprocess The storage volume for treated wastewater atevery household in each cluster was identified accord-ing to the optimisation results of AquaCycle (200 L ofwastewater storage per household in cluster 1 2 3 56 and 100 L of wastewater storage in cluster 4)

E Wastewater reuse at cluster scale

Wastewater treatment units were applied for eachcluster Household wastewater draining to a clusterwastewater storage tank was treated stored andsupplied for toilet flushing and garden irrigation forhouseholds and for open space irrigation It wasassumed that no water was lost in the treatmentprocess The treated wastewater storage volumes werecluster 1 7900 m3 cluster 2 4700 m3 cluster 38300 m3 cluster 4 1300 m3 cluster 5 9100 m3cluster 6 7200 m3 (based on the optimisation routineof AquaCycle)

29 Evaluation of strategies

As mentioned above the LA developed a vision for asustainable urban water system for the city This visionwas translated into tangible objectives the achieve-ment of which can be measured by sustainabilityindicators The score for these indicators were used toevaluate the strategies rather than by a thoroughengineering and economic feasibility study Some ofthe indicators could be evaluated in a quantitative wayusing the AquaCycle outputs others were evaluatedqualitatively

3 Results and discussion

31 Sustainability objectives and indicators

Based on interviews and general investigations it wasfound that the urban water system of Tel Aviv istypical for an advanced developed country but alsocharacterised by a number of un-sustainability factorswhich need improvement With regard to planning ofthe whole system it was noticed that lsquowater manage-mentrsquo is not addressed in the Strategic Plan of the city(Municipality of Tel Aviv 2006) and water indicatorsare therefore also not included in the set of indicatorsthat is used to monitor the development of the cityThis is somewhat surprising since the domestic waterconsumption in the city is higher than the amount thatcan be sustained from renewable water sources Thewater supply system is also threatened by insufficientmaintenance of the distribution system which causesbio-film growth and microbial pollution which in turnmay cause a higher chlorine demand One of theunderlying causes of the poor maintenance is lack ofsuitable financial resources for local government tomaintain the drinking water quality The same reasonsalso result in frequent leakages from the sewer system

Table 1 Formulated scenarios and factors until the year 2050

FactorPrecipitationdecrease

Temperatureincrease

Populationgrowth rate Urbanisation

Baseline scenario ndash ndash 22lsquoNo major changersquo scenario ndash ndash 22 20 of public open space is replaced

by residential area (10 in 2022 andanother 10 in 2046) road area isnot changed

lsquoNormalrsquo scenario 20 158C 22 20 of public open space is replacedby residential area (10 in 2022 andanother 10 in 2046) road area isnot changed

lsquoExtremersquo scenario 30 258C 22 20 of public open space is replacedby residential area (10 in 2022 andanother 10 in 2046) road area isnot changed

From 2023 onwards

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which causes severe pollution of the local aquiferwhich is one of the drinking water sources for the cityBasically all municipal wastewater is collected andtreated to a tertiary level but it is not utilised foragricultural irrigation within the region but in theNegev Urban parks in Tel Aviv are still irrigated withfresh water Stormwater is collected in a separatedrainage system but discharged directly to the seawithout any treatment There is no monitoring systemor research to evaluate the amount of stormwatergenerated in the city and its quality It is likely that TelAviv is overlooking the potential to use this nonconventional water resource The capacity of thedrainage system is not sufficient to prevent occasionalflooding Finally the un-sustainability of the systembecomes clear from the significant amount of energyused to transport fresh water over long distances anduphill (from the Sea of Galilee) to treat wastewater inan energy intensive system and finally to pump effluentto irrigation fields in the south of the country Thecommissioning of desalination plants will only increasethe energy consumption in the system

Based on this assessment the LA formulated aVision for sustainable urban water management in TelAviv lsquoTel Avivrsquos water system management will beestablished based on sustainability indicators andapply an efficient and integrated water managementto meet the water demand of citizens and for otherapplications with sufficient qualities and reasonableprices while the natural status of water resources isassuredrsquo The vision was translated into a set oftangible objectives and related indicators as shownin Table 2

32 Model calibration and simulation of wastewateroutput

The characteristics of the modelled clusters and therepresentative unit-block are outlined in Table 3 and 4The meteorological data the indoor water use profileand physical site characteristics were used as inputsfor the model The default calibration parameters(Table 5) initially were used and the model output interms of lsquoimported waterrsquo was compared with themunicipalities measured data on total water distrib-uted to the consumers The average amount oflsquoimported waterrsquo simulated by the model was about10 lower than the total water consumption Thelsquotrigger to irrigatersquo is the fraction of the optimal soilmoisture for plant growth which is still acceptable tothe user This trigger for private gardens and publicopen space was adjusted to 062 and as a result theaverage lsquoimported waterrsquo simulated by the model thenwas exactly the average volume of water distributed tothe consumers (Figure 5)

The monthly water consumption in the city isabout 40 higher in the summer irrigation seasonthan in the winter season The seasonal fluctuationcould be described well by the model throughirrigation of private gardens and public open spaceIt is likely that also the indoor water use is higher insummer but it is not possible in AquaCycle to changethe household indoor water consumption between theseasons Variation in imported water based on thefigures provided by the municipality (Figure 5) isrelatively large between some of the summer monthsespecially in 2004 and 2007 The reason for these largerfluctuations is unknown since the differences intemperature and potential evapotranspiration do notseem to explain such large fluctuations The model istherefore also not able to describe well these short-termfluctuations

Further calibration of the model was attemptedon observed wastewater flows from the wider TelAviv area (the Dan District) Unfortunately thewastewater flow from Tel Aviv is not measuredseparately from the wastewater flow from surround-ing municipalities It was therefore assumed that theamount of wastewater production per capita per yearin the various municipalities in the Dan District is thesame Therefore based on the population of TelAviv the amount of wastewater generated from TelAviv is estimated as 326 of total wastewaterproduction of the Dan District The wastewater flowssimulated by AquaCycle in the dry season (AprilndashOctober) were 18 lower than the flows based onmeasurements and the above described calculation(Figure 6) The simulated values may actually becloser to reality since the simulated values are90 of the indoor water consumption (about 31MCMmonth Figure 5) whereas the measured value(adjusted for population) is more than the actualindoor water consumption The higher flows inJanuary March and December are caused by wrongconnections between the stormwater drainage andfoul sewerage system The observed increase due tostormwater infiltration could be used to adjust thecalibration parameter lsquo of surface runoff as inflowrsquo(Table 5) The default value is 3 but a better fitwas achieved by using 7 This percentage is similarto the estimate of infiltration by Mekorot theoperator of the treatment plant (Aharoni personalcommunication)

33 The water balance of the system

The calibrated model was used to prepare the averageannual water balance for the city for the years2003ndash2007 (Figure 7) The water balance can be usedfor a fundamental evaluation of the sustainability of

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Table

2

Specificobjectives

andsustainabilityindicators

fortheurbanwatersystem

ofTel

Aviv

Specificobjective

Indicator

Unit

WaterPolicy

1TA

willraiseawarenessamongitscitizensabout

lsquowaterandsustainabilityrsquoandwillinvolvethe

publicin

decisionmaking

Thenumber

ofcitizensthatwillparticipate

inconsultativemeetings

Number

ofcitizensper

year

2TA

willmanageitsurbanwatersystem

inan

integratedwayintegratingaspects

ofwater

supplystorm

wateramp

wastew

atermanagem

ent

Theproductionofanintegratedurbanwater

managem

entplanforthecity

at2-yearintervals

Tim

elyproductionofintegratedplan

3A

setofsustainabilityindicators

willbeaccepted

andtheseindicators

willbeusedfordecision

makingandplanning

Referencesin

municipalplanningpolicy

documents

andgovernmentdecisionsto

the

sustainabilityindicators

Number

ofdocuments

withreferences

4TA

willstrengthen

thescientificbasisofitsdecision

makingconcerningthemanagem

entofitsUrban

WaterSystem

Thenumber

ofmunicipality

staffthatisusing

resultsfrom

scientificresearchin

theirdailywork

Number

ofstaff

WaterDem

andManagem

ent

5Thetotaldem

andin

TA

forfreshwateristo

be

reducedby10

by2050

Thereductionin

freshwatervolumeim

ported

tothecitycomparedto

the2009value

m3yearor

reduction

6Rainwaterandstorm

waterharvestingfor

non-potable

reuse

inthedomesticsectorwillbe

investigatedandapplied

ifoverallsustainability

ofthesystem

isincreased

Availabilityofastudyonrainwaterandor

storm

waterharvestingin

TA

Availabilityofstudy

Thenumber

ofhouseholdscollectingrainwater

Number

ofhouseholds

Thevolumeofrainwaterandorstorm

water

collectedandusedfornon-potable

use

m3year

7TA

willphase

outtheirrigationofurbanparks

withfreshwaterandwillonly

use

recycled

wastew

ater

forthispurpose

Thevolumeoffreshwaterorrecycled

wastew

aterusedforpark

irrigation

m3year

Percentageoftotalareairrigatedbyfreshwater

8

TA

willinfiltrate

storm

watergeneratedin

itsareainto

theaquiferherebyreducingthespillofwaterto

thesea

reducingthehydraulicloadto

theWWTPand

contributingto

aquifer

replenishmentTA

willtakecare

thatthestorm

waterisnotpolluted

Thepercentageofstorm

waterthatisinfiltrated

into

theaquifer

EnvironmentalProtection

9TA

willrestore

andprotect

itssurface

water

(YarkonRiver)

Thewaterquality

oftheYarkonriver

expressed

incommonly

usedwaterquality

parameters

(BODCOD)

various

10

TA

willminim

izetheenergyconsumptionin

theurban

watersystem

Thetotalquantity

ofenergyfrom

non-renew

able

sources

usedto

operate

theurbanwatersystem

includingwaterheatingin

thehouseholds

kWhyear

Socio-economy

11

TA

willsupply

waterofgoodquality

toitscitizens

atreasonable

price

insufficientqualities

ThefractionofsamplesanalyzedbytheMinistry

ofHealththatdoes

notsatisfythehealthcriteria

Thefrequency

ofsupply

interruptions

Downtimeper

year

12

TA

willensure

equityin

theaccessto

wateraswell

asto

irrigatedgreen

areas

Thespatialdistributionofwaterquality

and

frequency

ofserviceinterruptionsin

thecity

Mapwithwaterquality

andservice

interruptionfrequency

Thegreen

areaavailable

per

personandits

spatialdistribution

Mapwithm

2green

areaper

capita

13

TA

willreduce

therisk

offloodingin

vulnerable

arearsquos

toafrequency

thatisacceptable

toallstakeholderseven

under

future

clim

ate

changescenarios

Thenumber

ofpeople

affectedbyfloodingper

year

Number

ofpeople

per

year

Theeconomic

damagecausedbyflooding

USDyear

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the system The natural precipitation would not besufficient to satisfy current demand therefore largewater imports are required About 7 of the totalsystem inputs infiltrate into the groundwater andare in principle available for recovery from theaquifer In 2008 the municipality pumped slightlymore than 4 MCM from the aquifer therefore theTel Aviv urban area does not directly contribute toaquifer depletion The largest outflow from the city isthe wastewater flow which is treated and reused in theNegev The largest flux that is not beneficially used isthe stormwater flow If all stormwater would becaptured and used for urban purposes then about50 of the urban demand could be met by reclaimedstormwater

34 Results of the energy balance

The water balance for the city was used to calculatethe energy consumption in the urban water system(Figure 8) For each point of energy consumption inthe system the specific energy consumption in kWhm3

was determined as well as the proportion of the totalflow passing through that specific pathway Thus thetotal energy consumption in the system was calculatedas 328 kWhm3 This figure does not include energyconsumption for water heating in the householdThe largest energy consumption in the water systemitself is due to the long distance from the Lake ofGalilee seawater desalination wastewater treatmentand conveyance of effluent to the Negev The current

Table 3 Overview of cluster characteristics

Cluster 1 2 3 4 5 6

Population 80007 49095 84834 14384 91656 74964Total area (ha) 7451 6477 1459 6590 6470 9846Roads ( ha) 1135 976 1579 248 1180 1588Public open space (ha) 1490 648 2927 3927 647 646Unit-blocks (ha) 4825 4854 10084 2415 4643 7612

Table 4 Overview of unit-block characteristics

ClusterNumber ofunit-blocks

Averageoccupancy

Average areaof a unit-block (m2)

Area ofroof m2 (70)

Area ofgarden m2 (15)

Area ofpavement m2 (15)

1 36367 22 1327 929 199 1992 22316 22 2175 1523 326 3263 38561 22 2615 1831 392 3924 6538 22 3694 2586 554 5545 41662 22 1115 780 167 1676 34074 22 2234 1564 335 335

Table 5 Parameters used for the model calibration

Output Calibration parameter Default After calibration Units

Stormwater Percentage area of store 1 22 Pervious storage 1 capacity 32 mmPervious storage 2 capacity 240 mmRoof area maximum initial loss 0 mmEffective roof area 100 Paved area maximum initial loss 0 mmEffective paved area 100 Road area maximum initial loss 0 mmEffective road area 100 Base flow index 055 RatioBase flow recession constant 00025 Ratio

Wastewater Infiltration index 0095 RatioInfiltration store recession constant 012 Ratio of surface runoff as inflow 3 7

Imported water Garden trigger to irrigate 05 062 RatioPublic open space trigger to irrigate 042 062 Ratio

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contribution of desalination is small because only asmall fraction of the water use originates in desalina-tion plants but this is likely to increase in the futureNote that the specific energy consumption for desali-nation is several times the sum of all specific energyconsumption in the rest of the system

Figure 9 compares the energy consumption in TelAviv with some Australian cities (Kenway et al 2008)and with Zaragosa in Spain (SWITCH 2008 unpub-lished data) The energy costs in those cities for watertreatment and water pumping are highly variabledepending on quality and distance of the waterresource The energy consumption for wastewatertreatment and wastewater pumping (not includingconveyance to the Negev) is in the same range asobserved for the other cities

35 Evaluation of strategies ndash for the 2009 populationand average climatic conditions of 1994ndash2007

A Stormwater use and temporary aquifer storage

The number of days with rain in Tel Aviv is on average45 per year but only 31 days have more than 2 mm perday and therefore only a small number of days

Figure 5 Simulated volume of imported water and figures provided by the municipality from 2003 to 2007 (X-axis mmyy)

Figure 6 Total monthly wastewater production of Tel Aviv in year 2008 as estimated based on total Tel Avivrsquos share of totalDan Region wastewater production (lsquoEstimated datarsquo) and as simulated by AquaCycle

Figure 7 Tel Avivrsquos average water balance for 2003ndash2007(Stormwater flux includes the groundwater baseflow)

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generate significant runoff for stormwater harvestingAnother limiting factor in Tel Aviv is that the demandfor stormwater for irrigation is in the dry season whenthere is obviously no stormwater generation Still withthe cluster storage volumes indicated earlier (in total60000 m3 or 033 m3 per household) a reduction inwater import of 34 can be achieved Increasing totalstorage volume increases the percentage water savingbut reduces the efficiency of the tank (Figure 10) Aneconomic analysis is required to determine a feasiblevolume for the cluster stormwater tanks and this inturn determines the potential for water saving ofthis strategy Saving more than 5 by stormwaterharvesting is estimated to be very unlikely

B Rainwater harvesting

This strategy is more effective than strategy A in termsof overall water savings in the city and also moreefficient in terms of the volume of water saved per unit

rainwater tank volume (Figure 10) This difference iscaused by the higher quality of the rainwater whichallows (in this study) use for all household purposesFor a tank of 330 L per household the collectedrainwater is used for 32 and spilled from the tank for68 In strategy A the quality of the stormwater onlyallows use for toilet flushing and it is therefore mostlyspilled from the storage tanks during storm events (peryear 8 usage 92 spillage for the case with 033 m3

tank volume per household) In addition stormwaterin strategy A is in fact hardly used for irrigation sincethe storm events take place outside the irrigationseason Assuming that it is economical feasible toinstall a rainwater tank volume of about 075 m3 perhousehold then a total saving of 10 of water importsinto the city is possible Rozos et al (forthcoming)calculated that a 10 reduction of potable waterdemand in households in a Mediterranean climatewould increase the capital cost of the water supplysystem with about 40 while a 20 reduction in

Figure 8 The energy consuming components of Tel Avivrsquos water system

Figure 9 Energy use intensity of water and wastewater services by city (For Tel Aviv without energy consumption for theconveyance of effluent to irrigation areas in the Negev)Source Kenway et al (2008) SWITCH unpublished data

Urban Water Journal 113

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demand would be achievable when accepting a 160cost increase (ie even larger storage tanks)

C Permeable pavement

The surface of Tel Aviv is for 30 permeable and 70impermeable according to the calculated and esti-mated physical characteristics of the city (Tables 3and 4) The impermeable surface consists for 33 ofroads and pavements which could be made permeableby application of permeable types of pavementsAssuming that 80 of the roads and pavements canbe made permeable then the total impermeablesurface has been reduced by 26 Simulation withthe model showed that this would result in a reductionin stormwater generation of 20 (from 177 to 141MCM per year) The reduction in stormwater genera-tion is not only due to increased infiltration becausethe model simulates infiltration to increase onlyfrom 23 to 38 MCM per year The rest of thestormwater evaporates from the soil moisture storeand overflows via pervious surface runoff into thedrainage system

The purpose of this strategy would be to increaseaquifer recharge to allow more aquifer abstractionThe extra volume of abstraction per m2 of made-permeable pavement is about 02 m3m2 per yearA financial analysis will most likely show thatthis strategy is not feasible from a financial pointof view

D Wastewater reuse at unit-block scale

The model simulated grey wastewater treatmentstorage and reuse at household scale The storage

tank volumes based on the AquaCycle optimisationroutine resulted in a 21 reduced demand forimported water (99 MCM ) and a 27 reduction inwastewater flows from the city (94 MCM) Spillagefrom the tanks was small and therefore doubling thetank volumes changed the savings to 23 and 29 onlyrespectively Benefits of this strategy are reduced totaldemand which reduces the need for seawater desalina-tion and cost savings for wastewater collection andtreatment Costs of this strategy include costs forthe household-scale treatment and reuse system andthe reduction in effluent availability for agriculturein the Negev Potential health risks from wastewaterstorage and treatment at household and from potentialcross connections in double distribution networksshould also be addressed

E Wastewater reuse at cluster scale

The model simulated grey wastewater treatment andstorage at cluster level and reuse for toilet flushingirrigation of gardens and irrigation of open publicspace The storage tank volumes based on theAquaCycle optimisation routine resulted in a 25reduced demand for imported water (115 MCM )and a 31 reduction in wastewater flows from thecity (108 MCM) Doubling the tank volumeschanged the savings to 32 and 40 respectivelyThe saving of imported water per unit volumestorage tank for the smaller (021 m3household)and larger (042 m3 per household) tanks were 300and 194 m3m3 per year respectively Comparingthese figures to stormwater strategies A and B(Figure 10) clearly shows that wastewater reuse hasmore potential to save imported water and requires

Figure 10 Potential for yearly water saving by implementation of strategies A and B (for the 2009 population and averageclimatic conditions of 1994ndash2007)

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smaller tanks Reason for this difference is thatwastewater supply to the storage tanks is much lessfluctuating than stormwater flows

36 Evaluation of strategies under scenarios till2050 ndash demand for imported water (Indicator 5)

The demand for imported water in the city under thebaseline scenario increases from 472 MCM in 2009 to759 MCM in 2050 (Figure 11) due to populationgrowth The other scenarios slightly increase thedemand for imported water (778 MCM in 2050 forthe extreme scenario) The effect of climate change issmaller than one would maybe expect because thereduction in rainfall in the wet season does not increasethe demand for irrigation water since that demand isthere only in the dry season The increase intemperature during the dry season increases the

evapotranspiration and demand for irrigation waterbut only to a limited extend

The volume of water saved by the differentstrategies is constant with time for the lsquobaselinersquo andlsquono major changersquo scenarios but is affected by thechange in precipitation and temperature in the otherscenarios The volume of water saved by the strategy B(rainwater harvesting) will be less under the latterscenarios because the rainfall is less Figure 11 alsoshows that the volume of water saved in that strategyfluctuates from year to year with the fluctuations inyearly rainfall

The timing of the implementation of the strategiescould be based on keeping the total demand forimported water under a certain level Figure 12 showshow implementation of strategies B and D partlycancels the increase in demand due to populationgrowth

Figure 12 The simulated import of fresh water into Tel Aviv until 2050 based on phased implementation of strategies B and Dunder lsquonormalrsquo and lsquoextremersquo scenarios

Figure 11 The simulated import of fresh water into Tel Aviv until 2050 based on the lsquonormalrsquo scenario and different strategiesEmpirical data for 1996ndash2006 is also shown (source TahalMunicipality of Tel Aviv)

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37 Evaluation of strategies under scenarios till2050 ndash other indicators

Energy consumption per volume of water consumedcould be reduced by various measures such asreduction of physical leakage (Colombo et al 2002)or by optimising pump technology and pumpingschedules Energy consumption of the alternativestrategies was calculated to investigate their effecton the nexus water ndash energy The energy consumptionin the whole urban water system (Table 6) per m3

of water used (imported thorn reused water) in the citywas on average 289 kWh per m3 for the period2009ndash2050 (baseline scenario) Implementation of thestrategies affected the energy consumption in differentways Strategy B with a 330-L tank per householdresults in 274 kWhm3 mainly because rainwatersystems are estimated to use 0278 KWhm3 (Kenwayet al 2008) which is less energy intensive thenimporting water Wastewater treatment and reuse atcluster scale (strategy E 210-L tank per household)reduces energy consumption to 245 kWhm3 but thesame strategy at household (strategy D 200-L tankper household in cluster 1 2 3 5 6 and 100 L incluster 4) scale increases energy consumption till 318kWhm3 This is due to the higher energy con-sumption for on-site wastewater treatment systems(4 kWhm3 Steendam 2009) than for small waste-water treatment plants (estimated as 08 kWhm3

based on a reported range of 039 to 117 kWhm3 by

Young and Koopman 1991) Therefore it seems thatstrategy D performs best for both saving water andsaving energy

Implementation of the strategies will clearly affectsome of the indicators (Table 2 indicators 5 6 7 810) while other indicators are conditions for successfulimplementation (indicators 1 2 4 6) rather thanresults and yet other indicators are not likely to beaffected (indicators 11 12 13) The effect of thestrategies on groundwater quality and receiving surfacewater quality (indicator 9) is unsure and the topic ofongoing investigations

4 Conclusions

Based on the investigation of Tel Avivrsquos urban watersystem and the simulation results of AquaCyclefollowing conclusions are drawn

The volume of water imported into the city (onaverage 47 MCM per year) and the seasonalfluctuations in the period 2003ndash2007 was accu-rately described by the AquaCycle model usingthe input files on climate physical characteristicsof the city surface and average figures fordomestic end-use categories

Evaluation of several strategies to improve thesustainability of the water system showedthat rainwater harvesting from roofs for non-

Table 6 Energy consumption inventory of Tel Avivrsquos water system

Energy consumption(KWhm3)

Proportion oftotal amount

of water Source of data

Pumping water from the Lake ofGalilee to the city

13 90 Mekorot Company

Treating water from the Lake of Galilee 0 100 Mekorot Company(negligible since supplied toconsumer without treatment)

Treating amp pumping Sea water 39 2 Mekorot CompanyPumping groundwater from local wells 0371 8 Tel Aviv MunicipalityTreating groundwater from local wells 0 8 Tel Aviv Municipality

(negligible since supplied toconsumer without treatment)

Pumping for distributing water ndash North area 0103 135 Tel Aviv MunicipalityPumping for distributing water ndash South area 0077 72 Tel Aviv MunicipalityHeating water at household 407 27 EstimationWastewater collection 0111 100 Tel Aviv MunicipalityWastewater treatment 0425 100 Mekorot CompanyPumping treated wastewater for irrigation 145 100 Mekorot CompanyPumping stormwater 0 100 Tel Aviv Municipality

(negligible since dischargeddirectly to the Sea by gravity)

Total ( including heating water at household) 1427Total (not including household heating water ) 328

It was assumed that all water supplied by Mekorot to the city was taken from the Lake of Galilee rather than from groundwater pumpingstations closer to the city (such as Rosh HaAyin)

Based on 1 m3 supplied collected treated and reused

116 TTH Duong et al

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potable reuse in households is more promisingthan stormwater collection and reuse at clusterscale Assuming that it is feasible to install arainwater tank volume of about 075 m3 perhousehold then a total saving of 10 of waterimports into the city is possible

The overall water mass balance for the cityshowed that this rainwater harvesting strategywould reduce the amount of stormwater thatleaves the city per year from 22 MCM toabout 17 MCM which shows that othertechnologies or approaches are necessary ifone would like to make full beneficial use ofthis resource

Increasing rainwater infiltration for aquiferrecharge is most likely not financially sustainablesince the extra volume of recharge to allow moreaquifer abstraction is only 02 m3year per m2 ofmade-permeable pavement

The largest saving of water imports could beachieved by wastewater reuse for urban non-potable uses Wastewater collection storage(042 m3 per household) treatment and reuse atcluster scale is simulated to result in a 32 and40 reduction in water imports and wastewaterflows respectively

The most important factor of future scenariosfor water demand is population growth Effectsof climate change (reduced rainfall to a max-imum of 30 and increase in temperature to amaximum of 258C) on imported water weremuch smaller not more than 25 increase inthe extreme scenario This is in agreement withRozos et al (forthcoming) who have estimatedfor a Mediterranean climate an increase between0 and 4 depending on the capacity of therainwater harvesting scheme

Energy consumption in the urban water systemwas calculated as 289 kWh per m3 of volume ofwater used (import thorn reuse) in the city forthe period 2009ndash2050 Implementation of thestrategies affects the energy consumption indifferent ways Rainwater harvesting has somepotential to reduce energy consumption (to 274kWh per m3) but the best strategy in thisrespect is wastewater treatment and reuse atcluster scale (245 kWh per m3) The samestrategy at household scale causes an increasein energy consumption (318 kWh per m3)

The results of the model and the scenarioplanning study can be used to score a numberof the suggested sustainability indicators for theurban water system of Tel Aviv and as such canbe used by the multidisciplinary Water Club tosteer the city towards sustainability

Acknowledgements

The authors would like to thank the Dutch governmentfor its support through the NPT programme andthe European Commission for its support through theSWITCH project (FP6 Global Change and Ecosystems018530)

References

Butterworth JA Sutherland A Manning N Darteh BDziegielewska-Geitz M Eckart J Batchelor CMoriarty P Schouten T Da Silva C Verhagen Jand Bury PJ 2008 Building more effective partnershipsfor innovation in urban water management In Interna-tional Conference on Water and Urban DevelopmentParadigms Towards an integration of engineering designand management approaches 15ndash19 September 2008Katholieke Universiteit Leuven Belgium

Cities Alliance 2006 Guide to City Development StrategiesImproving urban performance Washington DC USApp 92

Colombo AF and Karney BW 2002 Energy and costs ofleaky pipes Toward comprehensive picture ASCEJournal of Water Resources Planning and Management128 (6) 441ndash450

ECAampD (European Climate Assessment amp Dataset Project)2008 Data records httpecaknminl [AccessedApril 2010]

Israel Ministry of Environmental Protection 2008 Israelrsquosadaption to climate change ndash Impacts and recommenda-tion httpwwwsvivagovil [Accessed April 2010]

Karka P Manoli E Lekkas DF and AssimacopoulosD 2007 A case study on integrated urban watermodelling using aquacyle In Proceedings of the 10thInternational Conference on Environmental Science ampTechnology Kos Island Greece 5ndash7 September 2007

Kenway SJ Priestley A Cook S Seo S Inman MGregory A and Hall M 2008 Energy use in theprovision and consumption of urban water in Australiaamp New Zealand Water for a Healthy country Flagshipreport series ISSN 1835ndash095X Water Service Associa-tion of Australia

Lundin M 2003 Indicators for measuring the sustainabilityof urban water system ndash A life cycle approach PhDdissertation Chalmers University of Technology

Makropoulos CK Memon FA Shirley-Smith C andButler D 2008a Futures An exploration of scenariosfor sustainable urban water management Water Policy10 345ndash373

Makropoulos CK Natsis K Liu S Mittas K andButler D 2008b Decision support for sustainableoption selection in integrated urban water managementEnvironmental Modelling amp Software 23 (12) 1448ndash1460

Mitchell V 2005 AquaCycle user guide A daily urban waterbalance model Australia Monash University Press

Mitchell V 2006 Applying integrated urban water manage-ment concepts A review of Australian experienceEnvironmental Management 37 (5) 589ndash605

Mitchell V Mein RG and McMahon TA 2001Modelling the urban water cycle Environmental Model-ling amp Software 16 615ndash629

Municipality of Tel Aviv 2006 City ndash The Strategic plan forTel Aviv Yafo Strategic Planning Unit Tel AvivMunicipality Israel

Urban Water Journal 117

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ober

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4

which causes severe pollution of the local aquiferwhich is one of the drinking water sources for the cityBasically all municipal wastewater is collected andtreated to a tertiary level but it is not utilised foragricultural irrigation within the region but in theNegev Urban parks in Tel Aviv are still irrigated withfresh water Stormwater is collected in a separatedrainage system but discharged directly to the seawithout any treatment There is no monitoring systemor research to evaluate the amount of stormwatergenerated in the city and its quality It is likely that TelAviv is overlooking the potential to use this nonconventional water resource The capacity of thedrainage system is not sufficient to prevent occasionalflooding Finally the un-sustainability of the systembecomes clear from the significant amount of energyused to transport fresh water over long distances anduphill (from the Sea of Galilee) to treat wastewater inan energy intensive system and finally to pump effluentto irrigation fields in the south of the country Thecommissioning of desalination plants will only increasethe energy consumption in the system

Based on this assessment the LA formulated aVision for sustainable urban water management in TelAviv lsquoTel Avivrsquos water system management will beestablished based on sustainability indicators andapply an efficient and integrated water managementto meet the water demand of citizens and for otherapplications with sufficient qualities and reasonableprices while the natural status of water resources isassuredrsquo The vision was translated into a set oftangible objectives and related indicators as shownin Table 2

32 Model calibration and simulation of wastewateroutput

The characteristics of the modelled clusters and therepresentative unit-block are outlined in Table 3 and 4The meteorological data the indoor water use profileand physical site characteristics were used as inputsfor the model The default calibration parameters(Table 5) initially were used and the model output interms of lsquoimported waterrsquo was compared with themunicipalities measured data on total water distrib-uted to the consumers The average amount oflsquoimported waterrsquo simulated by the model was about10 lower than the total water consumption Thelsquotrigger to irrigatersquo is the fraction of the optimal soilmoisture for plant growth which is still acceptable tothe user This trigger for private gardens and publicopen space was adjusted to 062 and as a result theaverage lsquoimported waterrsquo simulated by the model thenwas exactly the average volume of water distributed tothe consumers (Figure 5)

The monthly water consumption in the city isabout 40 higher in the summer irrigation seasonthan in the winter season The seasonal fluctuationcould be described well by the model throughirrigation of private gardens and public open spaceIt is likely that also the indoor water use is higher insummer but it is not possible in AquaCycle to changethe household indoor water consumption between theseasons Variation in imported water based on thefigures provided by the municipality (Figure 5) isrelatively large between some of the summer monthsespecially in 2004 and 2007 The reason for these largerfluctuations is unknown since the differences intemperature and potential evapotranspiration do notseem to explain such large fluctuations The model istherefore also not able to describe well these short-termfluctuations

Further calibration of the model was attemptedon observed wastewater flows from the wider TelAviv area (the Dan District) Unfortunately thewastewater flow from Tel Aviv is not measuredseparately from the wastewater flow from surround-ing municipalities It was therefore assumed that theamount of wastewater production per capita per yearin the various municipalities in the Dan District is thesame Therefore based on the population of TelAviv the amount of wastewater generated from TelAviv is estimated as 326 of total wastewaterproduction of the Dan District The wastewater flowssimulated by AquaCycle in the dry season (AprilndashOctober) were 18 lower than the flows based onmeasurements and the above described calculation(Figure 6) The simulated values may actually becloser to reality since the simulated values are90 of the indoor water consumption (about 31MCMmonth Figure 5) whereas the measured value(adjusted for population) is more than the actualindoor water consumption The higher flows inJanuary March and December are caused by wrongconnections between the stormwater drainage andfoul sewerage system The observed increase due tostormwater infiltration could be used to adjust thecalibration parameter lsquo of surface runoff as inflowrsquo(Table 5) The default value is 3 but a better fitwas achieved by using 7 This percentage is similarto the estimate of infiltration by Mekorot theoperator of the treatment plant (Aharoni personalcommunication)

33 The water balance of the system

The calibrated model was used to prepare the averageannual water balance for the city for the years2003ndash2007 (Figure 7) The water balance can be usedfor a fundamental evaluation of the sustainability of

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Table

2

Specificobjectives

andsustainabilityindicators

fortheurbanwatersystem

ofTel

Aviv

Specificobjective

Indicator

Unit

WaterPolicy

1TA

willraiseawarenessamongitscitizensabout

lsquowaterandsustainabilityrsquoandwillinvolvethe

publicin

decisionmaking

Thenumber

ofcitizensthatwillparticipate

inconsultativemeetings

Number

ofcitizensper

year

2TA

willmanageitsurbanwatersystem

inan

integratedwayintegratingaspects

ofwater

supplystorm

wateramp

wastew

atermanagem

ent

Theproductionofanintegratedurbanwater

managem

entplanforthecity

at2-yearintervals

Tim

elyproductionofintegratedplan

3A

setofsustainabilityindicators

willbeaccepted

andtheseindicators

willbeusedfordecision

makingandplanning

Referencesin

municipalplanningpolicy

documents

andgovernmentdecisionsto

the

sustainabilityindicators

Number

ofdocuments

withreferences

4TA

willstrengthen

thescientificbasisofitsdecision

makingconcerningthemanagem

entofitsUrban

WaterSystem

Thenumber

ofmunicipality

staffthatisusing

resultsfrom

scientificresearchin

theirdailywork

Number

ofstaff

WaterDem

andManagem

ent

5Thetotaldem

andin

TA

forfreshwateristo

be

reducedby10

by2050

Thereductionin

freshwatervolumeim

ported

tothecitycomparedto

the2009value

m3yearor

reduction

6Rainwaterandstorm

waterharvestingfor

non-potable

reuse

inthedomesticsectorwillbe

investigatedandapplied

ifoverallsustainability

ofthesystem

isincreased

Availabilityofastudyonrainwaterandor

storm

waterharvestingin

TA

Availabilityofstudy

Thenumber

ofhouseholdscollectingrainwater

Number

ofhouseholds

Thevolumeofrainwaterandorstorm

water

collectedandusedfornon-potable

use

m3year

7TA

willphase

outtheirrigationofurbanparks

withfreshwaterandwillonly

use

recycled

wastew

ater

forthispurpose

Thevolumeoffreshwaterorrecycled

wastew

aterusedforpark

irrigation

m3year

Percentageoftotalareairrigatedbyfreshwater

8

TA

willinfiltrate

storm

watergeneratedin

itsareainto

theaquiferherebyreducingthespillofwaterto

thesea

reducingthehydraulicloadto

theWWTPand

contributingto

aquifer

replenishmentTA

willtakecare

thatthestorm

waterisnotpolluted

Thepercentageofstorm

waterthatisinfiltrated

into

theaquifer

EnvironmentalProtection

9TA

willrestore

andprotect

itssurface

water

(YarkonRiver)

Thewaterquality

oftheYarkonriver

expressed

incommonly

usedwaterquality

parameters

(BODCOD)

various

10

TA

willminim

izetheenergyconsumptionin

theurban

watersystem

Thetotalquantity

ofenergyfrom

non-renew

able

sources

usedto

operate

theurbanwatersystem

includingwaterheatingin

thehouseholds

kWhyear

Socio-economy

11

TA

willsupply

waterofgoodquality

toitscitizens

atreasonable

price

insufficientqualities

ThefractionofsamplesanalyzedbytheMinistry

ofHealththatdoes

notsatisfythehealthcriteria

Thefrequency

ofsupply

interruptions

Downtimeper

year

12

TA

willensure

equityin

theaccessto

wateraswell

asto

irrigatedgreen

areas

Thespatialdistributionofwaterquality

and

frequency

ofserviceinterruptionsin

thecity

Mapwithwaterquality

andservice

interruptionfrequency

Thegreen

areaavailable

per

personandits

spatialdistribution

Mapwithm

2green

areaper

capita

13

TA

willreduce

therisk

offloodingin

vulnerable

arearsquos

toafrequency

thatisacceptable

toallstakeholderseven

under

future

clim

ate

changescenarios

Thenumber

ofpeople

affectedbyfloodingper

year

Number

ofpeople

per

year

Theeconomic

damagecausedbyflooding

USDyear

110 TTH Duong et al

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ober

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the system The natural precipitation would not besufficient to satisfy current demand therefore largewater imports are required About 7 of the totalsystem inputs infiltrate into the groundwater andare in principle available for recovery from theaquifer In 2008 the municipality pumped slightlymore than 4 MCM from the aquifer therefore theTel Aviv urban area does not directly contribute toaquifer depletion The largest outflow from the city isthe wastewater flow which is treated and reused in theNegev The largest flux that is not beneficially used isthe stormwater flow If all stormwater would becaptured and used for urban purposes then about50 of the urban demand could be met by reclaimedstormwater

34 Results of the energy balance

The water balance for the city was used to calculatethe energy consumption in the urban water system(Figure 8) For each point of energy consumption inthe system the specific energy consumption in kWhm3

was determined as well as the proportion of the totalflow passing through that specific pathway Thus thetotal energy consumption in the system was calculatedas 328 kWhm3 This figure does not include energyconsumption for water heating in the householdThe largest energy consumption in the water systemitself is due to the long distance from the Lake ofGalilee seawater desalination wastewater treatmentand conveyance of effluent to the Negev The current

Table 3 Overview of cluster characteristics

Cluster 1 2 3 4 5 6

Population 80007 49095 84834 14384 91656 74964Total area (ha) 7451 6477 1459 6590 6470 9846Roads ( ha) 1135 976 1579 248 1180 1588Public open space (ha) 1490 648 2927 3927 647 646Unit-blocks (ha) 4825 4854 10084 2415 4643 7612

Table 4 Overview of unit-block characteristics

ClusterNumber ofunit-blocks

Averageoccupancy

Average areaof a unit-block (m2)

Area ofroof m2 (70)

Area ofgarden m2 (15)

Area ofpavement m2 (15)

1 36367 22 1327 929 199 1992 22316 22 2175 1523 326 3263 38561 22 2615 1831 392 3924 6538 22 3694 2586 554 5545 41662 22 1115 780 167 1676 34074 22 2234 1564 335 335

Table 5 Parameters used for the model calibration

Output Calibration parameter Default After calibration Units

Stormwater Percentage area of store 1 22 Pervious storage 1 capacity 32 mmPervious storage 2 capacity 240 mmRoof area maximum initial loss 0 mmEffective roof area 100 Paved area maximum initial loss 0 mmEffective paved area 100 Road area maximum initial loss 0 mmEffective road area 100 Base flow index 055 RatioBase flow recession constant 00025 Ratio

Wastewater Infiltration index 0095 RatioInfiltration store recession constant 012 Ratio of surface runoff as inflow 3 7

Imported water Garden trigger to irrigate 05 062 RatioPublic open space trigger to irrigate 042 062 Ratio

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contribution of desalination is small because only asmall fraction of the water use originates in desalina-tion plants but this is likely to increase in the futureNote that the specific energy consumption for desali-nation is several times the sum of all specific energyconsumption in the rest of the system

Figure 9 compares the energy consumption in TelAviv with some Australian cities (Kenway et al 2008)and with Zaragosa in Spain (SWITCH 2008 unpub-lished data) The energy costs in those cities for watertreatment and water pumping are highly variabledepending on quality and distance of the waterresource The energy consumption for wastewatertreatment and wastewater pumping (not includingconveyance to the Negev) is in the same range asobserved for the other cities

35 Evaluation of strategies ndash for the 2009 populationand average climatic conditions of 1994ndash2007

A Stormwater use and temporary aquifer storage

The number of days with rain in Tel Aviv is on average45 per year but only 31 days have more than 2 mm perday and therefore only a small number of days

Figure 5 Simulated volume of imported water and figures provided by the municipality from 2003 to 2007 (X-axis mmyy)

Figure 6 Total monthly wastewater production of Tel Aviv in year 2008 as estimated based on total Tel Avivrsquos share of totalDan Region wastewater production (lsquoEstimated datarsquo) and as simulated by AquaCycle

Figure 7 Tel Avivrsquos average water balance for 2003ndash2007(Stormwater flux includes the groundwater baseflow)

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generate significant runoff for stormwater harvestingAnother limiting factor in Tel Aviv is that the demandfor stormwater for irrigation is in the dry season whenthere is obviously no stormwater generation Still withthe cluster storage volumes indicated earlier (in total60000 m3 or 033 m3 per household) a reduction inwater import of 34 can be achieved Increasing totalstorage volume increases the percentage water savingbut reduces the efficiency of the tank (Figure 10) Aneconomic analysis is required to determine a feasiblevolume for the cluster stormwater tanks and this inturn determines the potential for water saving ofthis strategy Saving more than 5 by stormwaterharvesting is estimated to be very unlikely

B Rainwater harvesting

This strategy is more effective than strategy A in termsof overall water savings in the city and also moreefficient in terms of the volume of water saved per unit

rainwater tank volume (Figure 10) This difference iscaused by the higher quality of the rainwater whichallows (in this study) use for all household purposesFor a tank of 330 L per household the collectedrainwater is used for 32 and spilled from the tank for68 In strategy A the quality of the stormwater onlyallows use for toilet flushing and it is therefore mostlyspilled from the storage tanks during storm events (peryear 8 usage 92 spillage for the case with 033 m3

tank volume per household) In addition stormwaterin strategy A is in fact hardly used for irrigation sincethe storm events take place outside the irrigationseason Assuming that it is economical feasible toinstall a rainwater tank volume of about 075 m3 perhousehold then a total saving of 10 of water importsinto the city is possible Rozos et al (forthcoming)calculated that a 10 reduction of potable waterdemand in households in a Mediterranean climatewould increase the capital cost of the water supplysystem with about 40 while a 20 reduction in

Figure 8 The energy consuming components of Tel Avivrsquos water system

Figure 9 Energy use intensity of water and wastewater services by city (For Tel Aviv without energy consumption for theconveyance of effluent to irrigation areas in the Negev)Source Kenway et al (2008) SWITCH unpublished data

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demand would be achievable when accepting a 160cost increase (ie even larger storage tanks)

C Permeable pavement

The surface of Tel Aviv is for 30 permeable and 70impermeable according to the calculated and esti-mated physical characteristics of the city (Tables 3and 4) The impermeable surface consists for 33 ofroads and pavements which could be made permeableby application of permeable types of pavementsAssuming that 80 of the roads and pavements canbe made permeable then the total impermeablesurface has been reduced by 26 Simulation withthe model showed that this would result in a reductionin stormwater generation of 20 (from 177 to 141MCM per year) The reduction in stormwater genera-tion is not only due to increased infiltration becausethe model simulates infiltration to increase onlyfrom 23 to 38 MCM per year The rest of thestormwater evaporates from the soil moisture storeand overflows via pervious surface runoff into thedrainage system

The purpose of this strategy would be to increaseaquifer recharge to allow more aquifer abstractionThe extra volume of abstraction per m2 of made-permeable pavement is about 02 m3m2 per yearA financial analysis will most likely show thatthis strategy is not feasible from a financial pointof view

D Wastewater reuse at unit-block scale

The model simulated grey wastewater treatmentstorage and reuse at household scale The storage

tank volumes based on the AquaCycle optimisationroutine resulted in a 21 reduced demand forimported water (99 MCM ) and a 27 reduction inwastewater flows from the city (94 MCM) Spillagefrom the tanks was small and therefore doubling thetank volumes changed the savings to 23 and 29 onlyrespectively Benefits of this strategy are reduced totaldemand which reduces the need for seawater desalina-tion and cost savings for wastewater collection andtreatment Costs of this strategy include costs forthe household-scale treatment and reuse system andthe reduction in effluent availability for agriculturein the Negev Potential health risks from wastewaterstorage and treatment at household and from potentialcross connections in double distribution networksshould also be addressed

E Wastewater reuse at cluster scale

The model simulated grey wastewater treatment andstorage at cluster level and reuse for toilet flushingirrigation of gardens and irrigation of open publicspace The storage tank volumes based on theAquaCycle optimisation routine resulted in a 25reduced demand for imported water (115 MCM )and a 31 reduction in wastewater flows from thecity (108 MCM) Doubling the tank volumeschanged the savings to 32 and 40 respectivelyThe saving of imported water per unit volumestorage tank for the smaller (021 m3household)and larger (042 m3 per household) tanks were 300and 194 m3m3 per year respectively Comparingthese figures to stormwater strategies A and B(Figure 10) clearly shows that wastewater reuse hasmore potential to save imported water and requires

Figure 10 Potential for yearly water saving by implementation of strategies A and B (for the 2009 population and averageclimatic conditions of 1994ndash2007)

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smaller tanks Reason for this difference is thatwastewater supply to the storage tanks is much lessfluctuating than stormwater flows

36 Evaluation of strategies under scenarios till2050 ndash demand for imported water (Indicator 5)

The demand for imported water in the city under thebaseline scenario increases from 472 MCM in 2009 to759 MCM in 2050 (Figure 11) due to populationgrowth The other scenarios slightly increase thedemand for imported water (778 MCM in 2050 forthe extreme scenario) The effect of climate change issmaller than one would maybe expect because thereduction in rainfall in the wet season does not increasethe demand for irrigation water since that demand isthere only in the dry season The increase intemperature during the dry season increases the

evapotranspiration and demand for irrigation waterbut only to a limited extend

The volume of water saved by the differentstrategies is constant with time for the lsquobaselinersquo andlsquono major changersquo scenarios but is affected by thechange in precipitation and temperature in the otherscenarios The volume of water saved by the strategy B(rainwater harvesting) will be less under the latterscenarios because the rainfall is less Figure 11 alsoshows that the volume of water saved in that strategyfluctuates from year to year with the fluctuations inyearly rainfall

The timing of the implementation of the strategiescould be based on keeping the total demand forimported water under a certain level Figure 12 showshow implementation of strategies B and D partlycancels the increase in demand due to populationgrowth

Figure 12 The simulated import of fresh water into Tel Aviv until 2050 based on phased implementation of strategies B and Dunder lsquonormalrsquo and lsquoextremersquo scenarios

Figure 11 The simulated import of fresh water into Tel Aviv until 2050 based on the lsquonormalrsquo scenario and different strategiesEmpirical data for 1996ndash2006 is also shown (source TahalMunicipality of Tel Aviv)

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37 Evaluation of strategies under scenarios till2050 ndash other indicators

Energy consumption per volume of water consumedcould be reduced by various measures such asreduction of physical leakage (Colombo et al 2002)or by optimising pump technology and pumpingschedules Energy consumption of the alternativestrategies was calculated to investigate their effecton the nexus water ndash energy The energy consumptionin the whole urban water system (Table 6) per m3

of water used (imported thorn reused water) in the citywas on average 289 kWh per m3 for the period2009ndash2050 (baseline scenario) Implementation of thestrategies affected the energy consumption in differentways Strategy B with a 330-L tank per householdresults in 274 kWhm3 mainly because rainwatersystems are estimated to use 0278 KWhm3 (Kenwayet al 2008) which is less energy intensive thenimporting water Wastewater treatment and reuse atcluster scale (strategy E 210-L tank per household)reduces energy consumption to 245 kWhm3 but thesame strategy at household (strategy D 200-L tankper household in cluster 1 2 3 5 6 and 100 L incluster 4) scale increases energy consumption till 318kWhm3 This is due to the higher energy con-sumption for on-site wastewater treatment systems(4 kWhm3 Steendam 2009) than for small waste-water treatment plants (estimated as 08 kWhm3

based on a reported range of 039 to 117 kWhm3 by

Young and Koopman 1991) Therefore it seems thatstrategy D performs best for both saving water andsaving energy

Implementation of the strategies will clearly affectsome of the indicators (Table 2 indicators 5 6 7 810) while other indicators are conditions for successfulimplementation (indicators 1 2 4 6) rather thanresults and yet other indicators are not likely to beaffected (indicators 11 12 13) The effect of thestrategies on groundwater quality and receiving surfacewater quality (indicator 9) is unsure and the topic ofongoing investigations

4 Conclusions

Based on the investigation of Tel Avivrsquos urban watersystem and the simulation results of AquaCyclefollowing conclusions are drawn

The volume of water imported into the city (onaverage 47 MCM per year) and the seasonalfluctuations in the period 2003ndash2007 was accu-rately described by the AquaCycle model usingthe input files on climate physical characteristicsof the city surface and average figures fordomestic end-use categories

Evaluation of several strategies to improve thesustainability of the water system showedthat rainwater harvesting from roofs for non-

Table 6 Energy consumption inventory of Tel Avivrsquos water system

Energy consumption(KWhm3)

Proportion oftotal amount

of water Source of data

Pumping water from the Lake ofGalilee to the city

13 90 Mekorot Company

Treating water from the Lake of Galilee 0 100 Mekorot Company(negligible since supplied toconsumer without treatment)

Treating amp pumping Sea water 39 2 Mekorot CompanyPumping groundwater from local wells 0371 8 Tel Aviv MunicipalityTreating groundwater from local wells 0 8 Tel Aviv Municipality

(negligible since supplied toconsumer without treatment)

Pumping for distributing water ndash North area 0103 135 Tel Aviv MunicipalityPumping for distributing water ndash South area 0077 72 Tel Aviv MunicipalityHeating water at household 407 27 EstimationWastewater collection 0111 100 Tel Aviv MunicipalityWastewater treatment 0425 100 Mekorot CompanyPumping treated wastewater for irrigation 145 100 Mekorot CompanyPumping stormwater 0 100 Tel Aviv Municipality

(negligible since dischargeddirectly to the Sea by gravity)

Total ( including heating water at household) 1427Total (not including household heating water ) 328

It was assumed that all water supplied by Mekorot to the city was taken from the Lake of Galilee rather than from groundwater pumpingstations closer to the city (such as Rosh HaAyin)

Based on 1 m3 supplied collected treated and reused

116 TTH Duong et al

Dow

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ober

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4

potable reuse in households is more promisingthan stormwater collection and reuse at clusterscale Assuming that it is feasible to install arainwater tank volume of about 075 m3 perhousehold then a total saving of 10 of waterimports into the city is possible

The overall water mass balance for the cityshowed that this rainwater harvesting strategywould reduce the amount of stormwater thatleaves the city per year from 22 MCM toabout 17 MCM which shows that othertechnologies or approaches are necessary ifone would like to make full beneficial use ofthis resource

Increasing rainwater infiltration for aquiferrecharge is most likely not financially sustainablesince the extra volume of recharge to allow moreaquifer abstraction is only 02 m3year per m2 ofmade-permeable pavement

The largest saving of water imports could beachieved by wastewater reuse for urban non-potable uses Wastewater collection storage(042 m3 per household) treatment and reuse atcluster scale is simulated to result in a 32 and40 reduction in water imports and wastewaterflows respectively

The most important factor of future scenariosfor water demand is population growth Effectsof climate change (reduced rainfall to a max-imum of 30 and increase in temperature to amaximum of 258C) on imported water weremuch smaller not more than 25 increase inthe extreme scenario This is in agreement withRozos et al (forthcoming) who have estimatedfor a Mediterranean climate an increase between0 and 4 depending on the capacity of therainwater harvesting scheme

Energy consumption in the urban water systemwas calculated as 289 kWh per m3 of volume ofwater used (import thorn reuse) in the city forthe period 2009ndash2050 Implementation of thestrategies affects the energy consumption indifferent ways Rainwater harvesting has somepotential to reduce energy consumption (to 274kWh per m3) but the best strategy in thisrespect is wastewater treatment and reuse atcluster scale (245 kWh per m3) The samestrategy at household scale causes an increasein energy consumption (318 kWh per m3)

The results of the model and the scenarioplanning study can be used to score a numberof the suggested sustainability indicators for theurban water system of Tel Aviv and as such canbe used by the multidisciplinary Water Club tosteer the city towards sustainability

Acknowledgements

The authors would like to thank the Dutch governmentfor its support through the NPT programme andthe European Commission for its support through theSWITCH project (FP6 Global Change and Ecosystems018530)

References

Butterworth JA Sutherland A Manning N Darteh BDziegielewska-Geitz M Eckart J Batchelor CMoriarty P Schouten T Da Silva C Verhagen Jand Bury PJ 2008 Building more effective partnershipsfor innovation in urban water management In Interna-tional Conference on Water and Urban DevelopmentParadigms Towards an integration of engineering designand management approaches 15ndash19 September 2008Katholieke Universiteit Leuven Belgium

Cities Alliance 2006 Guide to City Development StrategiesImproving urban performance Washington DC USApp 92

Colombo AF and Karney BW 2002 Energy and costs ofleaky pipes Toward comprehensive picture ASCEJournal of Water Resources Planning and Management128 (6) 441ndash450

ECAampD (European Climate Assessment amp Dataset Project)2008 Data records httpecaknminl [AccessedApril 2010]

Israel Ministry of Environmental Protection 2008 Israelrsquosadaption to climate change ndash Impacts and recommenda-tion httpwwwsvivagovil [Accessed April 2010]

Karka P Manoli E Lekkas DF and AssimacopoulosD 2007 A case study on integrated urban watermodelling using aquacyle In Proceedings of the 10thInternational Conference on Environmental Science ampTechnology Kos Island Greece 5ndash7 September 2007

Kenway SJ Priestley A Cook S Seo S Inman MGregory A and Hall M 2008 Energy use in theprovision and consumption of urban water in Australiaamp New Zealand Water for a Healthy country Flagshipreport series ISSN 1835ndash095X Water Service Associa-tion of Australia

Lundin M 2003 Indicators for measuring the sustainabilityof urban water system ndash A life cycle approach PhDdissertation Chalmers University of Technology

Makropoulos CK Memon FA Shirley-Smith C andButler D 2008a Futures An exploration of scenariosfor sustainable urban water management Water Policy10 345ndash373

Makropoulos CK Natsis K Liu S Mittas K andButler D 2008b Decision support for sustainableoption selection in integrated urban water managementEnvironmental Modelling amp Software 23 (12) 1448ndash1460

Mitchell V 2005 AquaCycle user guide A daily urban waterbalance model Australia Monash University Press

Mitchell V 2006 Applying integrated urban water manage-ment concepts A review of Australian experienceEnvironmental Management 37 (5) 589ndash605

Mitchell V Mein RG and McMahon TA 2001Modelling the urban water cycle Environmental Model-ling amp Software 16 615ndash629

Municipality of Tel Aviv 2006 City ndash The Strategic plan forTel Aviv Yafo Strategic Planning Unit Tel AvivMunicipality Israel

Urban Water Journal 117

Dow

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ibra

ry]

at 1

243

11

Oct

ober

201

4

Table

2

Specificobjectives

andsustainabilityindicators

fortheurbanwatersystem

ofTel

Aviv

Specificobjective

Indicator

Unit

WaterPolicy

1TA

willraiseawarenessamongitscitizensabout

lsquowaterandsustainabilityrsquoandwillinvolvethe

publicin

decisionmaking

Thenumber

ofcitizensthatwillparticipate

inconsultativemeetings

Number

ofcitizensper

year

2TA

willmanageitsurbanwatersystem

inan

integratedwayintegratingaspects

ofwater

supplystorm

wateramp

wastew

atermanagem

ent

Theproductionofanintegratedurbanwater

managem

entplanforthecity

at2-yearintervals

Tim

elyproductionofintegratedplan

3A

setofsustainabilityindicators

willbeaccepted

andtheseindicators

willbeusedfordecision

makingandplanning

Referencesin

municipalplanningpolicy

documents

andgovernmentdecisionsto

the

sustainabilityindicators

Number

ofdocuments

withreferences

4TA

willstrengthen

thescientificbasisofitsdecision

makingconcerningthemanagem

entofitsUrban

WaterSystem

Thenumber

ofmunicipality

staffthatisusing

resultsfrom

scientificresearchin

theirdailywork

Number

ofstaff

WaterDem

andManagem

ent

5Thetotaldem

andin

TA

forfreshwateristo

be

reducedby10

by2050

Thereductionin

freshwatervolumeim

ported

tothecitycomparedto

the2009value

m3yearor

reduction

6Rainwaterandstorm

waterharvestingfor

non-potable

reuse

inthedomesticsectorwillbe

investigatedandapplied

ifoverallsustainability

ofthesystem

isincreased

Availabilityofastudyonrainwaterandor

storm

waterharvestingin

TA

Availabilityofstudy

Thenumber

ofhouseholdscollectingrainwater

Number

ofhouseholds

Thevolumeofrainwaterandorstorm

water

collectedandusedfornon-potable

use

m3year

7TA

willphase

outtheirrigationofurbanparks

withfreshwaterandwillonly

use

recycled

wastew

ater

forthispurpose

Thevolumeoffreshwaterorrecycled

wastew

aterusedforpark

irrigation

m3year

Percentageoftotalareairrigatedbyfreshwater

8

TA

willinfiltrate

storm

watergeneratedin

itsareainto

theaquiferherebyreducingthespillofwaterto

thesea

reducingthehydraulicloadto

theWWTPand

contributingto

aquifer

replenishmentTA

willtakecare

thatthestorm

waterisnotpolluted

Thepercentageofstorm

waterthatisinfiltrated

into

theaquifer

EnvironmentalProtection

9TA

willrestore

andprotect

itssurface

water

(YarkonRiver)

Thewaterquality

oftheYarkonriver

expressed

incommonly

usedwaterquality

parameters

(BODCOD)

various

10

TA

willminim

izetheenergyconsumptionin

theurban

watersystem

Thetotalquantity

ofenergyfrom

non-renew

able

sources

usedto

operate

theurbanwatersystem

includingwaterheatingin

thehouseholds

kWhyear

Socio-economy

11

TA

willsupply

waterofgoodquality

toitscitizens

atreasonable

price

insufficientqualities

ThefractionofsamplesanalyzedbytheMinistry

ofHealththatdoes

notsatisfythehealthcriteria

Thefrequency

ofsupply

interruptions

Downtimeper

year

12

TA

willensure

equityin

theaccessto

wateraswell

asto

irrigatedgreen

areas

Thespatialdistributionofwaterquality

and

frequency

ofserviceinterruptionsin

thecity

Mapwithwaterquality

andservice

interruptionfrequency

Thegreen

areaavailable

per

personandits

spatialdistribution

Mapwithm

2green

areaper

capita

13

TA

willreduce

therisk

offloodingin

vulnerable

arearsquos

toafrequency

thatisacceptable

toallstakeholderseven

under

future

clim

ate

changescenarios

Thenumber

ofpeople

affectedbyfloodingper

year

Number

ofpeople

per

year

Theeconomic

damagecausedbyflooding

USDyear

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the system The natural precipitation would not besufficient to satisfy current demand therefore largewater imports are required About 7 of the totalsystem inputs infiltrate into the groundwater andare in principle available for recovery from theaquifer In 2008 the municipality pumped slightlymore than 4 MCM from the aquifer therefore theTel Aviv urban area does not directly contribute toaquifer depletion The largest outflow from the city isthe wastewater flow which is treated and reused in theNegev The largest flux that is not beneficially used isthe stormwater flow If all stormwater would becaptured and used for urban purposes then about50 of the urban demand could be met by reclaimedstormwater

34 Results of the energy balance

The water balance for the city was used to calculatethe energy consumption in the urban water system(Figure 8) For each point of energy consumption inthe system the specific energy consumption in kWhm3

was determined as well as the proportion of the totalflow passing through that specific pathway Thus thetotal energy consumption in the system was calculatedas 328 kWhm3 This figure does not include energyconsumption for water heating in the householdThe largest energy consumption in the water systemitself is due to the long distance from the Lake ofGalilee seawater desalination wastewater treatmentand conveyance of effluent to the Negev The current

Table 3 Overview of cluster characteristics

Cluster 1 2 3 4 5 6

Population 80007 49095 84834 14384 91656 74964Total area (ha) 7451 6477 1459 6590 6470 9846Roads ( ha) 1135 976 1579 248 1180 1588Public open space (ha) 1490 648 2927 3927 647 646Unit-blocks (ha) 4825 4854 10084 2415 4643 7612

Table 4 Overview of unit-block characteristics

ClusterNumber ofunit-blocks

Averageoccupancy

Average areaof a unit-block (m2)

Area ofroof m2 (70)

Area ofgarden m2 (15)

Area ofpavement m2 (15)

1 36367 22 1327 929 199 1992 22316 22 2175 1523 326 3263 38561 22 2615 1831 392 3924 6538 22 3694 2586 554 5545 41662 22 1115 780 167 1676 34074 22 2234 1564 335 335

Table 5 Parameters used for the model calibration

Output Calibration parameter Default After calibration Units

Stormwater Percentage area of store 1 22 Pervious storage 1 capacity 32 mmPervious storage 2 capacity 240 mmRoof area maximum initial loss 0 mmEffective roof area 100 Paved area maximum initial loss 0 mmEffective paved area 100 Road area maximum initial loss 0 mmEffective road area 100 Base flow index 055 RatioBase flow recession constant 00025 Ratio

Wastewater Infiltration index 0095 RatioInfiltration store recession constant 012 Ratio of surface runoff as inflow 3 7

Imported water Garden trigger to irrigate 05 062 RatioPublic open space trigger to irrigate 042 062 Ratio

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contribution of desalination is small because only asmall fraction of the water use originates in desalina-tion plants but this is likely to increase in the futureNote that the specific energy consumption for desali-nation is several times the sum of all specific energyconsumption in the rest of the system

Figure 9 compares the energy consumption in TelAviv with some Australian cities (Kenway et al 2008)and with Zaragosa in Spain (SWITCH 2008 unpub-lished data) The energy costs in those cities for watertreatment and water pumping are highly variabledepending on quality and distance of the waterresource The energy consumption for wastewatertreatment and wastewater pumping (not includingconveyance to the Negev) is in the same range asobserved for the other cities

35 Evaluation of strategies ndash for the 2009 populationand average climatic conditions of 1994ndash2007

A Stormwater use and temporary aquifer storage

The number of days with rain in Tel Aviv is on average45 per year but only 31 days have more than 2 mm perday and therefore only a small number of days

Figure 5 Simulated volume of imported water and figures provided by the municipality from 2003 to 2007 (X-axis mmyy)

Figure 6 Total monthly wastewater production of Tel Aviv in year 2008 as estimated based on total Tel Avivrsquos share of totalDan Region wastewater production (lsquoEstimated datarsquo) and as simulated by AquaCycle

Figure 7 Tel Avivrsquos average water balance for 2003ndash2007(Stormwater flux includes the groundwater baseflow)

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generate significant runoff for stormwater harvestingAnother limiting factor in Tel Aviv is that the demandfor stormwater for irrigation is in the dry season whenthere is obviously no stormwater generation Still withthe cluster storage volumes indicated earlier (in total60000 m3 or 033 m3 per household) a reduction inwater import of 34 can be achieved Increasing totalstorage volume increases the percentage water savingbut reduces the efficiency of the tank (Figure 10) Aneconomic analysis is required to determine a feasiblevolume for the cluster stormwater tanks and this inturn determines the potential for water saving ofthis strategy Saving more than 5 by stormwaterharvesting is estimated to be very unlikely

B Rainwater harvesting

This strategy is more effective than strategy A in termsof overall water savings in the city and also moreefficient in terms of the volume of water saved per unit

rainwater tank volume (Figure 10) This difference iscaused by the higher quality of the rainwater whichallows (in this study) use for all household purposesFor a tank of 330 L per household the collectedrainwater is used for 32 and spilled from the tank for68 In strategy A the quality of the stormwater onlyallows use for toilet flushing and it is therefore mostlyspilled from the storage tanks during storm events (peryear 8 usage 92 spillage for the case with 033 m3

tank volume per household) In addition stormwaterin strategy A is in fact hardly used for irrigation sincethe storm events take place outside the irrigationseason Assuming that it is economical feasible toinstall a rainwater tank volume of about 075 m3 perhousehold then a total saving of 10 of water importsinto the city is possible Rozos et al (forthcoming)calculated that a 10 reduction of potable waterdemand in households in a Mediterranean climatewould increase the capital cost of the water supplysystem with about 40 while a 20 reduction in

Figure 8 The energy consuming components of Tel Avivrsquos water system

Figure 9 Energy use intensity of water and wastewater services by city (For Tel Aviv without energy consumption for theconveyance of effluent to irrigation areas in the Negev)Source Kenway et al (2008) SWITCH unpublished data

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demand would be achievable when accepting a 160cost increase (ie even larger storage tanks)

C Permeable pavement

The surface of Tel Aviv is for 30 permeable and 70impermeable according to the calculated and esti-mated physical characteristics of the city (Tables 3and 4) The impermeable surface consists for 33 ofroads and pavements which could be made permeableby application of permeable types of pavementsAssuming that 80 of the roads and pavements canbe made permeable then the total impermeablesurface has been reduced by 26 Simulation withthe model showed that this would result in a reductionin stormwater generation of 20 (from 177 to 141MCM per year) The reduction in stormwater genera-tion is not only due to increased infiltration becausethe model simulates infiltration to increase onlyfrom 23 to 38 MCM per year The rest of thestormwater evaporates from the soil moisture storeand overflows via pervious surface runoff into thedrainage system

The purpose of this strategy would be to increaseaquifer recharge to allow more aquifer abstractionThe extra volume of abstraction per m2 of made-permeable pavement is about 02 m3m2 per yearA financial analysis will most likely show thatthis strategy is not feasible from a financial pointof view

D Wastewater reuse at unit-block scale

The model simulated grey wastewater treatmentstorage and reuse at household scale The storage

tank volumes based on the AquaCycle optimisationroutine resulted in a 21 reduced demand forimported water (99 MCM ) and a 27 reduction inwastewater flows from the city (94 MCM) Spillagefrom the tanks was small and therefore doubling thetank volumes changed the savings to 23 and 29 onlyrespectively Benefits of this strategy are reduced totaldemand which reduces the need for seawater desalina-tion and cost savings for wastewater collection andtreatment Costs of this strategy include costs forthe household-scale treatment and reuse system andthe reduction in effluent availability for agriculturein the Negev Potential health risks from wastewaterstorage and treatment at household and from potentialcross connections in double distribution networksshould also be addressed

E Wastewater reuse at cluster scale

The model simulated grey wastewater treatment andstorage at cluster level and reuse for toilet flushingirrigation of gardens and irrigation of open publicspace The storage tank volumes based on theAquaCycle optimisation routine resulted in a 25reduced demand for imported water (115 MCM )and a 31 reduction in wastewater flows from thecity (108 MCM) Doubling the tank volumeschanged the savings to 32 and 40 respectivelyThe saving of imported water per unit volumestorage tank for the smaller (021 m3household)and larger (042 m3 per household) tanks were 300and 194 m3m3 per year respectively Comparingthese figures to stormwater strategies A and B(Figure 10) clearly shows that wastewater reuse hasmore potential to save imported water and requires

Figure 10 Potential for yearly water saving by implementation of strategies A and B (for the 2009 population and averageclimatic conditions of 1994ndash2007)

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smaller tanks Reason for this difference is thatwastewater supply to the storage tanks is much lessfluctuating than stormwater flows

36 Evaluation of strategies under scenarios till2050 ndash demand for imported water (Indicator 5)

The demand for imported water in the city under thebaseline scenario increases from 472 MCM in 2009 to759 MCM in 2050 (Figure 11) due to populationgrowth The other scenarios slightly increase thedemand for imported water (778 MCM in 2050 forthe extreme scenario) The effect of climate change issmaller than one would maybe expect because thereduction in rainfall in the wet season does not increasethe demand for irrigation water since that demand isthere only in the dry season The increase intemperature during the dry season increases the

evapotranspiration and demand for irrigation waterbut only to a limited extend

The volume of water saved by the differentstrategies is constant with time for the lsquobaselinersquo andlsquono major changersquo scenarios but is affected by thechange in precipitation and temperature in the otherscenarios The volume of water saved by the strategy B(rainwater harvesting) will be less under the latterscenarios because the rainfall is less Figure 11 alsoshows that the volume of water saved in that strategyfluctuates from year to year with the fluctuations inyearly rainfall

The timing of the implementation of the strategiescould be based on keeping the total demand forimported water under a certain level Figure 12 showshow implementation of strategies B and D partlycancels the increase in demand due to populationgrowth

Figure 12 The simulated import of fresh water into Tel Aviv until 2050 based on phased implementation of strategies B and Dunder lsquonormalrsquo and lsquoextremersquo scenarios

Figure 11 The simulated import of fresh water into Tel Aviv until 2050 based on the lsquonormalrsquo scenario and different strategiesEmpirical data for 1996ndash2006 is also shown (source TahalMunicipality of Tel Aviv)

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37 Evaluation of strategies under scenarios till2050 ndash other indicators

Energy consumption per volume of water consumedcould be reduced by various measures such asreduction of physical leakage (Colombo et al 2002)or by optimising pump technology and pumpingschedules Energy consumption of the alternativestrategies was calculated to investigate their effecton the nexus water ndash energy The energy consumptionin the whole urban water system (Table 6) per m3

of water used (imported thorn reused water) in the citywas on average 289 kWh per m3 for the period2009ndash2050 (baseline scenario) Implementation of thestrategies affected the energy consumption in differentways Strategy B with a 330-L tank per householdresults in 274 kWhm3 mainly because rainwatersystems are estimated to use 0278 KWhm3 (Kenwayet al 2008) which is less energy intensive thenimporting water Wastewater treatment and reuse atcluster scale (strategy E 210-L tank per household)reduces energy consumption to 245 kWhm3 but thesame strategy at household (strategy D 200-L tankper household in cluster 1 2 3 5 6 and 100 L incluster 4) scale increases energy consumption till 318kWhm3 This is due to the higher energy con-sumption for on-site wastewater treatment systems(4 kWhm3 Steendam 2009) than for small waste-water treatment plants (estimated as 08 kWhm3

based on a reported range of 039 to 117 kWhm3 by

Young and Koopman 1991) Therefore it seems thatstrategy D performs best for both saving water andsaving energy

Implementation of the strategies will clearly affectsome of the indicators (Table 2 indicators 5 6 7 810) while other indicators are conditions for successfulimplementation (indicators 1 2 4 6) rather thanresults and yet other indicators are not likely to beaffected (indicators 11 12 13) The effect of thestrategies on groundwater quality and receiving surfacewater quality (indicator 9) is unsure and the topic ofongoing investigations

4 Conclusions

Based on the investigation of Tel Avivrsquos urban watersystem and the simulation results of AquaCyclefollowing conclusions are drawn

The volume of water imported into the city (onaverage 47 MCM per year) and the seasonalfluctuations in the period 2003ndash2007 was accu-rately described by the AquaCycle model usingthe input files on climate physical characteristicsof the city surface and average figures fordomestic end-use categories

Evaluation of several strategies to improve thesustainability of the water system showedthat rainwater harvesting from roofs for non-

Table 6 Energy consumption inventory of Tel Avivrsquos water system

Energy consumption(KWhm3)

Proportion oftotal amount

of water Source of data

Pumping water from the Lake ofGalilee to the city

13 90 Mekorot Company

Treating water from the Lake of Galilee 0 100 Mekorot Company(negligible since supplied toconsumer without treatment)

Treating amp pumping Sea water 39 2 Mekorot CompanyPumping groundwater from local wells 0371 8 Tel Aviv MunicipalityTreating groundwater from local wells 0 8 Tel Aviv Municipality

(negligible since supplied toconsumer without treatment)

Pumping for distributing water ndash North area 0103 135 Tel Aviv MunicipalityPumping for distributing water ndash South area 0077 72 Tel Aviv MunicipalityHeating water at household 407 27 EstimationWastewater collection 0111 100 Tel Aviv MunicipalityWastewater treatment 0425 100 Mekorot CompanyPumping treated wastewater for irrigation 145 100 Mekorot CompanyPumping stormwater 0 100 Tel Aviv Municipality

(negligible since dischargeddirectly to the Sea by gravity)

Total ( including heating water at household) 1427Total (not including household heating water ) 328

It was assumed that all water supplied by Mekorot to the city was taken from the Lake of Galilee rather than from groundwater pumpingstations closer to the city (such as Rosh HaAyin)

Based on 1 m3 supplied collected treated and reused

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potable reuse in households is more promisingthan stormwater collection and reuse at clusterscale Assuming that it is feasible to install arainwater tank volume of about 075 m3 perhousehold then a total saving of 10 of waterimports into the city is possible

The overall water mass balance for the cityshowed that this rainwater harvesting strategywould reduce the amount of stormwater thatleaves the city per year from 22 MCM toabout 17 MCM which shows that othertechnologies or approaches are necessary ifone would like to make full beneficial use ofthis resource

Increasing rainwater infiltration for aquiferrecharge is most likely not financially sustainablesince the extra volume of recharge to allow moreaquifer abstraction is only 02 m3year per m2 ofmade-permeable pavement

The largest saving of water imports could beachieved by wastewater reuse for urban non-potable uses Wastewater collection storage(042 m3 per household) treatment and reuse atcluster scale is simulated to result in a 32 and40 reduction in water imports and wastewaterflows respectively

The most important factor of future scenariosfor water demand is population growth Effectsof climate change (reduced rainfall to a max-imum of 30 and increase in temperature to amaximum of 258C) on imported water weremuch smaller not more than 25 increase inthe extreme scenario This is in agreement withRozos et al (forthcoming) who have estimatedfor a Mediterranean climate an increase between0 and 4 depending on the capacity of therainwater harvesting scheme

Energy consumption in the urban water systemwas calculated as 289 kWh per m3 of volume ofwater used (import thorn reuse) in the city forthe period 2009ndash2050 Implementation of thestrategies affects the energy consumption indifferent ways Rainwater harvesting has somepotential to reduce energy consumption (to 274kWh per m3) but the best strategy in thisrespect is wastewater treatment and reuse atcluster scale (245 kWh per m3) The samestrategy at household scale causes an increasein energy consumption (318 kWh per m3)

The results of the model and the scenarioplanning study can be used to score a numberof the suggested sustainability indicators for theurban water system of Tel Aviv and as such canbe used by the multidisciplinary Water Club tosteer the city towards sustainability

Acknowledgements

The authors would like to thank the Dutch governmentfor its support through the NPT programme andthe European Commission for its support through theSWITCH project (FP6 Global Change and Ecosystems018530)

References

Butterworth JA Sutherland A Manning N Darteh BDziegielewska-Geitz M Eckart J Batchelor CMoriarty P Schouten T Da Silva C Verhagen Jand Bury PJ 2008 Building more effective partnershipsfor innovation in urban water management In Interna-tional Conference on Water and Urban DevelopmentParadigms Towards an integration of engineering designand management approaches 15ndash19 September 2008Katholieke Universiteit Leuven Belgium

Cities Alliance 2006 Guide to City Development StrategiesImproving urban performance Washington DC USApp 92

Colombo AF and Karney BW 2002 Energy and costs ofleaky pipes Toward comprehensive picture ASCEJournal of Water Resources Planning and Management128 (6) 441ndash450

ECAampD (European Climate Assessment amp Dataset Project)2008 Data records httpecaknminl [AccessedApril 2010]

Israel Ministry of Environmental Protection 2008 Israelrsquosadaption to climate change ndash Impacts and recommenda-tion httpwwwsvivagovil [Accessed April 2010]

Karka P Manoli E Lekkas DF and AssimacopoulosD 2007 A case study on integrated urban watermodelling using aquacyle In Proceedings of the 10thInternational Conference on Environmental Science ampTechnology Kos Island Greece 5ndash7 September 2007

Kenway SJ Priestley A Cook S Seo S Inman MGregory A and Hall M 2008 Energy use in theprovision and consumption of urban water in Australiaamp New Zealand Water for a Healthy country Flagshipreport series ISSN 1835ndash095X Water Service Associa-tion of Australia

Lundin M 2003 Indicators for measuring the sustainabilityof urban water system ndash A life cycle approach PhDdissertation Chalmers University of Technology

Makropoulos CK Memon FA Shirley-Smith C andButler D 2008a Futures An exploration of scenariosfor sustainable urban water management Water Policy10 345ndash373

Makropoulos CK Natsis K Liu S Mittas K andButler D 2008b Decision support for sustainableoption selection in integrated urban water managementEnvironmental Modelling amp Software 23 (12) 1448ndash1460

Mitchell V 2005 AquaCycle user guide A daily urban waterbalance model Australia Monash University Press

Mitchell V 2006 Applying integrated urban water manage-ment concepts A review of Australian experienceEnvironmental Management 37 (5) 589ndash605

Mitchell V Mein RG and McMahon TA 2001Modelling the urban water cycle Environmental Model-ling amp Software 16 615ndash629

Municipality of Tel Aviv 2006 City ndash The Strategic plan forTel Aviv Yafo Strategic Planning Unit Tel AvivMunicipality Israel

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the system The natural precipitation would not besufficient to satisfy current demand therefore largewater imports are required About 7 of the totalsystem inputs infiltrate into the groundwater andare in principle available for recovery from theaquifer In 2008 the municipality pumped slightlymore than 4 MCM from the aquifer therefore theTel Aviv urban area does not directly contribute toaquifer depletion The largest outflow from the city isthe wastewater flow which is treated and reused in theNegev The largest flux that is not beneficially used isthe stormwater flow If all stormwater would becaptured and used for urban purposes then about50 of the urban demand could be met by reclaimedstormwater

34 Results of the energy balance

The water balance for the city was used to calculatethe energy consumption in the urban water system(Figure 8) For each point of energy consumption inthe system the specific energy consumption in kWhm3

was determined as well as the proportion of the totalflow passing through that specific pathway Thus thetotal energy consumption in the system was calculatedas 328 kWhm3 This figure does not include energyconsumption for water heating in the householdThe largest energy consumption in the water systemitself is due to the long distance from the Lake ofGalilee seawater desalination wastewater treatmentand conveyance of effluent to the Negev The current

Table 3 Overview of cluster characteristics

Cluster 1 2 3 4 5 6

Population 80007 49095 84834 14384 91656 74964Total area (ha) 7451 6477 1459 6590 6470 9846Roads ( ha) 1135 976 1579 248 1180 1588Public open space (ha) 1490 648 2927 3927 647 646Unit-blocks (ha) 4825 4854 10084 2415 4643 7612

Table 4 Overview of unit-block characteristics

ClusterNumber ofunit-blocks

Averageoccupancy

Average areaof a unit-block (m2)

Area ofroof m2 (70)

Area ofgarden m2 (15)

Area ofpavement m2 (15)

1 36367 22 1327 929 199 1992 22316 22 2175 1523 326 3263 38561 22 2615 1831 392 3924 6538 22 3694 2586 554 5545 41662 22 1115 780 167 1676 34074 22 2234 1564 335 335

Table 5 Parameters used for the model calibration

Output Calibration parameter Default After calibration Units

Stormwater Percentage area of store 1 22 Pervious storage 1 capacity 32 mmPervious storage 2 capacity 240 mmRoof area maximum initial loss 0 mmEffective roof area 100 Paved area maximum initial loss 0 mmEffective paved area 100 Road area maximum initial loss 0 mmEffective road area 100 Base flow index 055 RatioBase flow recession constant 00025 Ratio

Wastewater Infiltration index 0095 RatioInfiltration store recession constant 012 Ratio of surface runoff as inflow 3 7

Imported water Garden trigger to irrigate 05 062 RatioPublic open space trigger to irrigate 042 062 Ratio

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contribution of desalination is small because only asmall fraction of the water use originates in desalina-tion plants but this is likely to increase in the futureNote that the specific energy consumption for desali-nation is several times the sum of all specific energyconsumption in the rest of the system

Figure 9 compares the energy consumption in TelAviv with some Australian cities (Kenway et al 2008)and with Zaragosa in Spain (SWITCH 2008 unpub-lished data) The energy costs in those cities for watertreatment and water pumping are highly variabledepending on quality and distance of the waterresource The energy consumption for wastewatertreatment and wastewater pumping (not includingconveyance to the Negev) is in the same range asobserved for the other cities

35 Evaluation of strategies ndash for the 2009 populationand average climatic conditions of 1994ndash2007

A Stormwater use and temporary aquifer storage

The number of days with rain in Tel Aviv is on average45 per year but only 31 days have more than 2 mm perday and therefore only a small number of days

Figure 5 Simulated volume of imported water and figures provided by the municipality from 2003 to 2007 (X-axis mmyy)

Figure 6 Total monthly wastewater production of Tel Aviv in year 2008 as estimated based on total Tel Avivrsquos share of totalDan Region wastewater production (lsquoEstimated datarsquo) and as simulated by AquaCycle

Figure 7 Tel Avivrsquos average water balance for 2003ndash2007(Stormwater flux includes the groundwater baseflow)

112 TTH Duong et al

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generate significant runoff for stormwater harvestingAnother limiting factor in Tel Aviv is that the demandfor stormwater for irrigation is in the dry season whenthere is obviously no stormwater generation Still withthe cluster storage volumes indicated earlier (in total60000 m3 or 033 m3 per household) a reduction inwater import of 34 can be achieved Increasing totalstorage volume increases the percentage water savingbut reduces the efficiency of the tank (Figure 10) Aneconomic analysis is required to determine a feasiblevolume for the cluster stormwater tanks and this inturn determines the potential for water saving ofthis strategy Saving more than 5 by stormwaterharvesting is estimated to be very unlikely

B Rainwater harvesting

This strategy is more effective than strategy A in termsof overall water savings in the city and also moreefficient in terms of the volume of water saved per unit

rainwater tank volume (Figure 10) This difference iscaused by the higher quality of the rainwater whichallows (in this study) use for all household purposesFor a tank of 330 L per household the collectedrainwater is used for 32 and spilled from the tank for68 In strategy A the quality of the stormwater onlyallows use for toilet flushing and it is therefore mostlyspilled from the storage tanks during storm events (peryear 8 usage 92 spillage for the case with 033 m3

tank volume per household) In addition stormwaterin strategy A is in fact hardly used for irrigation sincethe storm events take place outside the irrigationseason Assuming that it is economical feasible toinstall a rainwater tank volume of about 075 m3 perhousehold then a total saving of 10 of water importsinto the city is possible Rozos et al (forthcoming)calculated that a 10 reduction of potable waterdemand in households in a Mediterranean climatewould increase the capital cost of the water supplysystem with about 40 while a 20 reduction in

Figure 8 The energy consuming components of Tel Avivrsquos water system

Figure 9 Energy use intensity of water and wastewater services by city (For Tel Aviv without energy consumption for theconveyance of effluent to irrigation areas in the Negev)Source Kenway et al (2008) SWITCH unpublished data

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demand would be achievable when accepting a 160cost increase (ie even larger storage tanks)

C Permeable pavement

The surface of Tel Aviv is for 30 permeable and 70impermeable according to the calculated and esti-mated physical characteristics of the city (Tables 3and 4) The impermeable surface consists for 33 ofroads and pavements which could be made permeableby application of permeable types of pavementsAssuming that 80 of the roads and pavements canbe made permeable then the total impermeablesurface has been reduced by 26 Simulation withthe model showed that this would result in a reductionin stormwater generation of 20 (from 177 to 141MCM per year) The reduction in stormwater genera-tion is not only due to increased infiltration becausethe model simulates infiltration to increase onlyfrom 23 to 38 MCM per year The rest of thestormwater evaporates from the soil moisture storeand overflows via pervious surface runoff into thedrainage system

The purpose of this strategy would be to increaseaquifer recharge to allow more aquifer abstractionThe extra volume of abstraction per m2 of made-permeable pavement is about 02 m3m2 per yearA financial analysis will most likely show thatthis strategy is not feasible from a financial pointof view

D Wastewater reuse at unit-block scale

The model simulated grey wastewater treatmentstorage and reuse at household scale The storage

tank volumes based on the AquaCycle optimisationroutine resulted in a 21 reduced demand forimported water (99 MCM ) and a 27 reduction inwastewater flows from the city (94 MCM) Spillagefrom the tanks was small and therefore doubling thetank volumes changed the savings to 23 and 29 onlyrespectively Benefits of this strategy are reduced totaldemand which reduces the need for seawater desalina-tion and cost savings for wastewater collection andtreatment Costs of this strategy include costs forthe household-scale treatment and reuse system andthe reduction in effluent availability for agriculturein the Negev Potential health risks from wastewaterstorage and treatment at household and from potentialcross connections in double distribution networksshould also be addressed

E Wastewater reuse at cluster scale

The model simulated grey wastewater treatment andstorage at cluster level and reuse for toilet flushingirrigation of gardens and irrigation of open publicspace The storage tank volumes based on theAquaCycle optimisation routine resulted in a 25reduced demand for imported water (115 MCM )and a 31 reduction in wastewater flows from thecity (108 MCM) Doubling the tank volumeschanged the savings to 32 and 40 respectivelyThe saving of imported water per unit volumestorage tank for the smaller (021 m3household)and larger (042 m3 per household) tanks were 300and 194 m3m3 per year respectively Comparingthese figures to stormwater strategies A and B(Figure 10) clearly shows that wastewater reuse hasmore potential to save imported water and requires

Figure 10 Potential for yearly water saving by implementation of strategies A and B (for the 2009 population and averageclimatic conditions of 1994ndash2007)

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smaller tanks Reason for this difference is thatwastewater supply to the storage tanks is much lessfluctuating than stormwater flows

36 Evaluation of strategies under scenarios till2050 ndash demand for imported water (Indicator 5)

The demand for imported water in the city under thebaseline scenario increases from 472 MCM in 2009 to759 MCM in 2050 (Figure 11) due to populationgrowth The other scenarios slightly increase thedemand for imported water (778 MCM in 2050 forthe extreme scenario) The effect of climate change issmaller than one would maybe expect because thereduction in rainfall in the wet season does not increasethe demand for irrigation water since that demand isthere only in the dry season The increase intemperature during the dry season increases the

evapotranspiration and demand for irrigation waterbut only to a limited extend

The volume of water saved by the differentstrategies is constant with time for the lsquobaselinersquo andlsquono major changersquo scenarios but is affected by thechange in precipitation and temperature in the otherscenarios The volume of water saved by the strategy B(rainwater harvesting) will be less under the latterscenarios because the rainfall is less Figure 11 alsoshows that the volume of water saved in that strategyfluctuates from year to year with the fluctuations inyearly rainfall

The timing of the implementation of the strategiescould be based on keeping the total demand forimported water under a certain level Figure 12 showshow implementation of strategies B and D partlycancels the increase in demand due to populationgrowth

Figure 12 The simulated import of fresh water into Tel Aviv until 2050 based on phased implementation of strategies B and Dunder lsquonormalrsquo and lsquoextremersquo scenarios

Figure 11 The simulated import of fresh water into Tel Aviv until 2050 based on the lsquonormalrsquo scenario and different strategiesEmpirical data for 1996ndash2006 is also shown (source TahalMunicipality of Tel Aviv)

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37 Evaluation of strategies under scenarios till2050 ndash other indicators

Energy consumption per volume of water consumedcould be reduced by various measures such asreduction of physical leakage (Colombo et al 2002)or by optimising pump technology and pumpingschedules Energy consumption of the alternativestrategies was calculated to investigate their effecton the nexus water ndash energy The energy consumptionin the whole urban water system (Table 6) per m3

of water used (imported thorn reused water) in the citywas on average 289 kWh per m3 for the period2009ndash2050 (baseline scenario) Implementation of thestrategies affected the energy consumption in differentways Strategy B with a 330-L tank per householdresults in 274 kWhm3 mainly because rainwatersystems are estimated to use 0278 KWhm3 (Kenwayet al 2008) which is less energy intensive thenimporting water Wastewater treatment and reuse atcluster scale (strategy E 210-L tank per household)reduces energy consumption to 245 kWhm3 but thesame strategy at household (strategy D 200-L tankper household in cluster 1 2 3 5 6 and 100 L incluster 4) scale increases energy consumption till 318kWhm3 This is due to the higher energy con-sumption for on-site wastewater treatment systems(4 kWhm3 Steendam 2009) than for small waste-water treatment plants (estimated as 08 kWhm3

based on a reported range of 039 to 117 kWhm3 by

Young and Koopman 1991) Therefore it seems thatstrategy D performs best for both saving water andsaving energy

Implementation of the strategies will clearly affectsome of the indicators (Table 2 indicators 5 6 7 810) while other indicators are conditions for successfulimplementation (indicators 1 2 4 6) rather thanresults and yet other indicators are not likely to beaffected (indicators 11 12 13) The effect of thestrategies on groundwater quality and receiving surfacewater quality (indicator 9) is unsure and the topic ofongoing investigations

4 Conclusions

Based on the investigation of Tel Avivrsquos urban watersystem and the simulation results of AquaCyclefollowing conclusions are drawn

The volume of water imported into the city (onaverage 47 MCM per year) and the seasonalfluctuations in the period 2003ndash2007 was accu-rately described by the AquaCycle model usingthe input files on climate physical characteristicsof the city surface and average figures fordomestic end-use categories

Evaluation of several strategies to improve thesustainability of the water system showedthat rainwater harvesting from roofs for non-

Table 6 Energy consumption inventory of Tel Avivrsquos water system

Energy consumption(KWhm3)

Proportion oftotal amount

of water Source of data

Pumping water from the Lake ofGalilee to the city

13 90 Mekorot Company

Treating water from the Lake of Galilee 0 100 Mekorot Company(negligible since supplied toconsumer without treatment)

Treating amp pumping Sea water 39 2 Mekorot CompanyPumping groundwater from local wells 0371 8 Tel Aviv MunicipalityTreating groundwater from local wells 0 8 Tel Aviv Municipality

(negligible since supplied toconsumer without treatment)

Pumping for distributing water ndash North area 0103 135 Tel Aviv MunicipalityPumping for distributing water ndash South area 0077 72 Tel Aviv MunicipalityHeating water at household 407 27 EstimationWastewater collection 0111 100 Tel Aviv MunicipalityWastewater treatment 0425 100 Mekorot CompanyPumping treated wastewater for irrigation 145 100 Mekorot CompanyPumping stormwater 0 100 Tel Aviv Municipality

(negligible since dischargeddirectly to the Sea by gravity)

Total ( including heating water at household) 1427Total (not including household heating water ) 328

It was assumed that all water supplied by Mekorot to the city was taken from the Lake of Galilee rather than from groundwater pumpingstations closer to the city (such as Rosh HaAyin)

Based on 1 m3 supplied collected treated and reused

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potable reuse in households is more promisingthan stormwater collection and reuse at clusterscale Assuming that it is feasible to install arainwater tank volume of about 075 m3 perhousehold then a total saving of 10 of waterimports into the city is possible

The overall water mass balance for the cityshowed that this rainwater harvesting strategywould reduce the amount of stormwater thatleaves the city per year from 22 MCM toabout 17 MCM which shows that othertechnologies or approaches are necessary ifone would like to make full beneficial use ofthis resource

Increasing rainwater infiltration for aquiferrecharge is most likely not financially sustainablesince the extra volume of recharge to allow moreaquifer abstraction is only 02 m3year per m2 ofmade-permeable pavement

The largest saving of water imports could beachieved by wastewater reuse for urban non-potable uses Wastewater collection storage(042 m3 per household) treatment and reuse atcluster scale is simulated to result in a 32 and40 reduction in water imports and wastewaterflows respectively

The most important factor of future scenariosfor water demand is population growth Effectsof climate change (reduced rainfall to a max-imum of 30 and increase in temperature to amaximum of 258C) on imported water weremuch smaller not more than 25 increase inthe extreme scenario This is in agreement withRozos et al (forthcoming) who have estimatedfor a Mediterranean climate an increase between0 and 4 depending on the capacity of therainwater harvesting scheme

Energy consumption in the urban water systemwas calculated as 289 kWh per m3 of volume ofwater used (import thorn reuse) in the city forthe period 2009ndash2050 Implementation of thestrategies affects the energy consumption indifferent ways Rainwater harvesting has somepotential to reduce energy consumption (to 274kWh per m3) but the best strategy in thisrespect is wastewater treatment and reuse atcluster scale (245 kWh per m3) The samestrategy at household scale causes an increasein energy consumption (318 kWh per m3)

The results of the model and the scenarioplanning study can be used to score a numberof the suggested sustainability indicators for theurban water system of Tel Aviv and as such canbe used by the multidisciplinary Water Club tosteer the city towards sustainability

Acknowledgements

The authors would like to thank the Dutch governmentfor its support through the NPT programme andthe European Commission for its support through theSWITCH project (FP6 Global Change and Ecosystems018530)

References

Butterworth JA Sutherland A Manning N Darteh BDziegielewska-Geitz M Eckart J Batchelor CMoriarty P Schouten T Da Silva C Verhagen Jand Bury PJ 2008 Building more effective partnershipsfor innovation in urban water management In Interna-tional Conference on Water and Urban DevelopmentParadigms Towards an integration of engineering designand management approaches 15ndash19 September 2008Katholieke Universiteit Leuven Belgium

Cities Alliance 2006 Guide to City Development StrategiesImproving urban performance Washington DC USApp 92

Colombo AF and Karney BW 2002 Energy and costs ofleaky pipes Toward comprehensive picture ASCEJournal of Water Resources Planning and Management128 (6) 441ndash450

ECAampD (European Climate Assessment amp Dataset Project)2008 Data records httpecaknminl [AccessedApril 2010]

Israel Ministry of Environmental Protection 2008 Israelrsquosadaption to climate change ndash Impacts and recommenda-tion httpwwwsvivagovil [Accessed April 2010]

Karka P Manoli E Lekkas DF and AssimacopoulosD 2007 A case study on integrated urban watermodelling using aquacyle In Proceedings of the 10thInternational Conference on Environmental Science ampTechnology Kos Island Greece 5ndash7 September 2007

Kenway SJ Priestley A Cook S Seo S Inman MGregory A and Hall M 2008 Energy use in theprovision and consumption of urban water in Australiaamp New Zealand Water for a Healthy country Flagshipreport series ISSN 1835ndash095X Water Service Associa-tion of Australia

Lundin M 2003 Indicators for measuring the sustainabilityof urban water system ndash A life cycle approach PhDdissertation Chalmers University of Technology

Makropoulos CK Memon FA Shirley-Smith C andButler D 2008a Futures An exploration of scenariosfor sustainable urban water management Water Policy10 345ndash373

Makropoulos CK Natsis K Liu S Mittas K andButler D 2008b Decision support for sustainableoption selection in integrated urban water managementEnvironmental Modelling amp Software 23 (12) 1448ndash1460

Mitchell V 2005 AquaCycle user guide A daily urban waterbalance model Australia Monash University Press

Mitchell V 2006 Applying integrated urban water manage-ment concepts A review of Australian experienceEnvironmental Management 37 (5) 589ndash605

Mitchell V Mein RG and McMahon TA 2001Modelling the urban water cycle Environmental Model-ling amp Software 16 615ndash629

Municipality of Tel Aviv 2006 City ndash The Strategic plan forTel Aviv Yafo Strategic Planning Unit Tel AvivMunicipality Israel

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contribution of desalination is small because only asmall fraction of the water use originates in desalina-tion plants but this is likely to increase in the futureNote that the specific energy consumption for desali-nation is several times the sum of all specific energyconsumption in the rest of the system

Figure 9 compares the energy consumption in TelAviv with some Australian cities (Kenway et al 2008)and with Zaragosa in Spain (SWITCH 2008 unpub-lished data) The energy costs in those cities for watertreatment and water pumping are highly variabledepending on quality and distance of the waterresource The energy consumption for wastewatertreatment and wastewater pumping (not includingconveyance to the Negev) is in the same range asobserved for the other cities

35 Evaluation of strategies ndash for the 2009 populationand average climatic conditions of 1994ndash2007

A Stormwater use and temporary aquifer storage

The number of days with rain in Tel Aviv is on average45 per year but only 31 days have more than 2 mm perday and therefore only a small number of days

Figure 5 Simulated volume of imported water and figures provided by the municipality from 2003 to 2007 (X-axis mmyy)

Figure 6 Total monthly wastewater production of Tel Aviv in year 2008 as estimated based on total Tel Avivrsquos share of totalDan Region wastewater production (lsquoEstimated datarsquo) and as simulated by AquaCycle

Figure 7 Tel Avivrsquos average water balance for 2003ndash2007(Stormwater flux includes the groundwater baseflow)

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generate significant runoff for stormwater harvestingAnother limiting factor in Tel Aviv is that the demandfor stormwater for irrigation is in the dry season whenthere is obviously no stormwater generation Still withthe cluster storage volumes indicated earlier (in total60000 m3 or 033 m3 per household) a reduction inwater import of 34 can be achieved Increasing totalstorage volume increases the percentage water savingbut reduces the efficiency of the tank (Figure 10) Aneconomic analysis is required to determine a feasiblevolume for the cluster stormwater tanks and this inturn determines the potential for water saving ofthis strategy Saving more than 5 by stormwaterharvesting is estimated to be very unlikely

B Rainwater harvesting

This strategy is more effective than strategy A in termsof overall water savings in the city and also moreefficient in terms of the volume of water saved per unit

rainwater tank volume (Figure 10) This difference iscaused by the higher quality of the rainwater whichallows (in this study) use for all household purposesFor a tank of 330 L per household the collectedrainwater is used for 32 and spilled from the tank for68 In strategy A the quality of the stormwater onlyallows use for toilet flushing and it is therefore mostlyspilled from the storage tanks during storm events (peryear 8 usage 92 spillage for the case with 033 m3

tank volume per household) In addition stormwaterin strategy A is in fact hardly used for irrigation sincethe storm events take place outside the irrigationseason Assuming that it is economical feasible toinstall a rainwater tank volume of about 075 m3 perhousehold then a total saving of 10 of water importsinto the city is possible Rozos et al (forthcoming)calculated that a 10 reduction of potable waterdemand in households in a Mediterranean climatewould increase the capital cost of the water supplysystem with about 40 while a 20 reduction in

Figure 8 The energy consuming components of Tel Avivrsquos water system

Figure 9 Energy use intensity of water and wastewater services by city (For Tel Aviv without energy consumption for theconveyance of effluent to irrigation areas in the Negev)Source Kenway et al (2008) SWITCH unpublished data

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demand would be achievable when accepting a 160cost increase (ie even larger storage tanks)

C Permeable pavement

The surface of Tel Aviv is for 30 permeable and 70impermeable according to the calculated and esti-mated physical characteristics of the city (Tables 3and 4) The impermeable surface consists for 33 ofroads and pavements which could be made permeableby application of permeable types of pavementsAssuming that 80 of the roads and pavements canbe made permeable then the total impermeablesurface has been reduced by 26 Simulation withthe model showed that this would result in a reductionin stormwater generation of 20 (from 177 to 141MCM per year) The reduction in stormwater genera-tion is not only due to increased infiltration becausethe model simulates infiltration to increase onlyfrom 23 to 38 MCM per year The rest of thestormwater evaporates from the soil moisture storeand overflows via pervious surface runoff into thedrainage system

The purpose of this strategy would be to increaseaquifer recharge to allow more aquifer abstractionThe extra volume of abstraction per m2 of made-permeable pavement is about 02 m3m2 per yearA financial analysis will most likely show thatthis strategy is not feasible from a financial pointof view

D Wastewater reuse at unit-block scale

The model simulated grey wastewater treatmentstorage and reuse at household scale The storage

tank volumes based on the AquaCycle optimisationroutine resulted in a 21 reduced demand forimported water (99 MCM ) and a 27 reduction inwastewater flows from the city (94 MCM) Spillagefrom the tanks was small and therefore doubling thetank volumes changed the savings to 23 and 29 onlyrespectively Benefits of this strategy are reduced totaldemand which reduces the need for seawater desalina-tion and cost savings for wastewater collection andtreatment Costs of this strategy include costs forthe household-scale treatment and reuse system andthe reduction in effluent availability for agriculturein the Negev Potential health risks from wastewaterstorage and treatment at household and from potentialcross connections in double distribution networksshould also be addressed

E Wastewater reuse at cluster scale

The model simulated grey wastewater treatment andstorage at cluster level and reuse for toilet flushingirrigation of gardens and irrigation of open publicspace The storage tank volumes based on theAquaCycle optimisation routine resulted in a 25reduced demand for imported water (115 MCM )and a 31 reduction in wastewater flows from thecity (108 MCM) Doubling the tank volumeschanged the savings to 32 and 40 respectivelyThe saving of imported water per unit volumestorage tank for the smaller (021 m3household)and larger (042 m3 per household) tanks were 300and 194 m3m3 per year respectively Comparingthese figures to stormwater strategies A and B(Figure 10) clearly shows that wastewater reuse hasmore potential to save imported water and requires

Figure 10 Potential for yearly water saving by implementation of strategies A and B (for the 2009 population and averageclimatic conditions of 1994ndash2007)

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smaller tanks Reason for this difference is thatwastewater supply to the storage tanks is much lessfluctuating than stormwater flows

36 Evaluation of strategies under scenarios till2050 ndash demand for imported water (Indicator 5)

The demand for imported water in the city under thebaseline scenario increases from 472 MCM in 2009 to759 MCM in 2050 (Figure 11) due to populationgrowth The other scenarios slightly increase thedemand for imported water (778 MCM in 2050 forthe extreme scenario) The effect of climate change issmaller than one would maybe expect because thereduction in rainfall in the wet season does not increasethe demand for irrigation water since that demand isthere only in the dry season The increase intemperature during the dry season increases the

evapotranspiration and demand for irrigation waterbut only to a limited extend

The volume of water saved by the differentstrategies is constant with time for the lsquobaselinersquo andlsquono major changersquo scenarios but is affected by thechange in precipitation and temperature in the otherscenarios The volume of water saved by the strategy B(rainwater harvesting) will be less under the latterscenarios because the rainfall is less Figure 11 alsoshows that the volume of water saved in that strategyfluctuates from year to year with the fluctuations inyearly rainfall

The timing of the implementation of the strategiescould be based on keeping the total demand forimported water under a certain level Figure 12 showshow implementation of strategies B and D partlycancels the increase in demand due to populationgrowth

Figure 12 The simulated import of fresh water into Tel Aviv until 2050 based on phased implementation of strategies B and Dunder lsquonormalrsquo and lsquoextremersquo scenarios

Figure 11 The simulated import of fresh water into Tel Aviv until 2050 based on the lsquonormalrsquo scenario and different strategiesEmpirical data for 1996ndash2006 is also shown (source TahalMunicipality of Tel Aviv)

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37 Evaluation of strategies under scenarios till2050 ndash other indicators

Energy consumption per volume of water consumedcould be reduced by various measures such asreduction of physical leakage (Colombo et al 2002)or by optimising pump technology and pumpingschedules Energy consumption of the alternativestrategies was calculated to investigate their effecton the nexus water ndash energy The energy consumptionin the whole urban water system (Table 6) per m3

of water used (imported thorn reused water) in the citywas on average 289 kWh per m3 for the period2009ndash2050 (baseline scenario) Implementation of thestrategies affected the energy consumption in differentways Strategy B with a 330-L tank per householdresults in 274 kWhm3 mainly because rainwatersystems are estimated to use 0278 KWhm3 (Kenwayet al 2008) which is less energy intensive thenimporting water Wastewater treatment and reuse atcluster scale (strategy E 210-L tank per household)reduces energy consumption to 245 kWhm3 but thesame strategy at household (strategy D 200-L tankper household in cluster 1 2 3 5 6 and 100 L incluster 4) scale increases energy consumption till 318kWhm3 This is due to the higher energy con-sumption for on-site wastewater treatment systems(4 kWhm3 Steendam 2009) than for small waste-water treatment plants (estimated as 08 kWhm3

based on a reported range of 039 to 117 kWhm3 by

Young and Koopman 1991) Therefore it seems thatstrategy D performs best for both saving water andsaving energy

Implementation of the strategies will clearly affectsome of the indicators (Table 2 indicators 5 6 7 810) while other indicators are conditions for successfulimplementation (indicators 1 2 4 6) rather thanresults and yet other indicators are not likely to beaffected (indicators 11 12 13) The effect of thestrategies on groundwater quality and receiving surfacewater quality (indicator 9) is unsure and the topic ofongoing investigations

4 Conclusions

Based on the investigation of Tel Avivrsquos urban watersystem and the simulation results of AquaCyclefollowing conclusions are drawn

The volume of water imported into the city (onaverage 47 MCM per year) and the seasonalfluctuations in the period 2003ndash2007 was accu-rately described by the AquaCycle model usingthe input files on climate physical characteristicsof the city surface and average figures fordomestic end-use categories

Evaluation of several strategies to improve thesustainability of the water system showedthat rainwater harvesting from roofs for non-

Table 6 Energy consumption inventory of Tel Avivrsquos water system

Energy consumption(KWhm3)

Proportion oftotal amount

of water Source of data

Pumping water from the Lake ofGalilee to the city

13 90 Mekorot Company

Treating water from the Lake of Galilee 0 100 Mekorot Company(negligible since supplied toconsumer without treatment)

Treating amp pumping Sea water 39 2 Mekorot CompanyPumping groundwater from local wells 0371 8 Tel Aviv MunicipalityTreating groundwater from local wells 0 8 Tel Aviv Municipality

(negligible since supplied toconsumer without treatment)

Pumping for distributing water ndash North area 0103 135 Tel Aviv MunicipalityPumping for distributing water ndash South area 0077 72 Tel Aviv MunicipalityHeating water at household 407 27 EstimationWastewater collection 0111 100 Tel Aviv MunicipalityWastewater treatment 0425 100 Mekorot CompanyPumping treated wastewater for irrigation 145 100 Mekorot CompanyPumping stormwater 0 100 Tel Aviv Municipality

(negligible since dischargeddirectly to the Sea by gravity)

Total ( including heating water at household) 1427Total (not including household heating water ) 328

It was assumed that all water supplied by Mekorot to the city was taken from the Lake of Galilee rather than from groundwater pumpingstations closer to the city (such as Rosh HaAyin)

Based on 1 m3 supplied collected treated and reused

116 TTH Duong et al

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ober

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potable reuse in households is more promisingthan stormwater collection and reuse at clusterscale Assuming that it is feasible to install arainwater tank volume of about 075 m3 perhousehold then a total saving of 10 of waterimports into the city is possible

The overall water mass balance for the cityshowed that this rainwater harvesting strategywould reduce the amount of stormwater thatleaves the city per year from 22 MCM toabout 17 MCM which shows that othertechnologies or approaches are necessary ifone would like to make full beneficial use ofthis resource

Increasing rainwater infiltration for aquiferrecharge is most likely not financially sustainablesince the extra volume of recharge to allow moreaquifer abstraction is only 02 m3year per m2 ofmade-permeable pavement

The largest saving of water imports could beachieved by wastewater reuse for urban non-potable uses Wastewater collection storage(042 m3 per household) treatment and reuse atcluster scale is simulated to result in a 32 and40 reduction in water imports and wastewaterflows respectively

The most important factor of future scenariosfor water demand is population growth Effectsof climate change (reduced rainfall to a max-imum of 30 and increase in temperature to amaximum of 258C) on imported water weremuch smaller not more than 25 increase inthe extreme scenario This is in agreement withRozos et al (forthcoming) who have estimatedfor a Mediterranean climate an increase between0 and 4 depending on the capacity of therainwater harvesting scheme

Energy consumption in the urban water systemwas calculated as 289 kWh per m3 of volume ofwater used (import thorn reuse) in the city forthe period 2009ndash2050 Implementation of thestrategies affects the energy consumption indifferent ways Rainwater harvesting has somepotential to reduce energy consumption (to 274kWh per m3) but the best strategy in thisrespect is wastewater treatment and reuse atcluster scale (245 kWh per m3) The samestrategy at household scale causes an increasein energy consumption (318 kWh per m3)

The results of the model and the scenarioplanning study can be used to score a numberof the suggested sustainability indicators for theurban water system of Tel Aviv and as such canbe used by the multidisciplinary Water Club tosteer the city towards sustainability

Acknowledgements

The authors would like to thank the Dutch governmentfor its support through the NPT programme andthe European Commission for its support through theSWITCH project (FP6 Global Change and Ecosystems018530)

References

Butterworth JA Sutherland A Manning N Darteh BDziegielewska-Geitz M Eckart J Batchelor CMoriarty P Schouten T Da Silva C Verhagen Jand Bury PJ 2008 Building more effective partnershipsfor innovation in urban water management In Interna-tional Conference on Water and Urban DevelopmentParadigms Towards an integration of engineering designand management approaches 15ndash19 September 2008Katholieke Universiteit Leuven Belgium

Cities Alliance 2006 Guide to City Development StrategiesImproving urban performance Washington DC USApp 92

Colombo AF and Karney BW 2002 Energy and costs ofleaky pipes Toward comprehensive picture ASCEJournal of Water Resources Planning and Management128 (6) 441ndash450

ECAampD (European Climate Assessment amp Dataset Project)2008 Data records httpecaknminl [AccessedApril 2010]

Israel Ministry of Environmental Protection 2008 Israelrsquosadaption to climate change ndash Impacts and recommenda-tion httpwwwsvivagovil [Accessed April 2010]

Karka P Manoli E Lekkas DF and AssimacopoulosD 2007 A case study on integrated urban watermodelling using aquacyle In Proceedings of the 10thInternational Conference on Environmental Science ampTechnology Kos Island Greece 5ndash7 September 2007

Kenway SJ Priestley A Cook S Seo S Inman MGregory A and Hall M 2008 Energy use in theprovision and consumption of urban water in Australiaamp New Zealand Water for a Healthy country Flagshipreport series ISSN 1835ndash095X Water Service Associa-tion of Australia

Lundin M 2003 Indicators for measuring the sustainabilityof urban water system ndash A life cycle approach PhDdissertation Chalmers University of Technology

Makropoulos CK Memon FA Shirley-Smith C andButler D 2008a Futures An exploration of scenariosfor sustainable urban water management Water Policy10 345ndash373

Makropoulos CK Natsis K Liu S Mittas K andButler D 2008b Decision support for sustainableoption selection in integrated urban water managementEnvironmental Modelling amp Software 23 (12) 1448ndash1460

Mitchell V 2005 AquaCycle user guide A daily urban waterbalance model Australia Monash University Press

Mitchell V 2006 Applying integrated urban water manage-ment concepts A review of Australian experienceEnvironmental Management 37 (5) 589ndash605

Mitchell V Mein RG and McMahon TA 2001Modelling the urban water cycle Environmental Model-ling amp Software 16 615ndash629

Municipality of Tel Aviv 2006 City ndash The Strategic plan forTel Aviv Yafo Strategic Planning Unit Tel AvivMunicipality Israel

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generate significant runoff for stormwater harvestingAnother limiting factor in Tel Aviv is that the demandfor stormwater for irrigation is in the dry season whenthere is obviously no stormwater generation Still withthe cluster storage volumes indicated earlier (in total60000 m3 or 033 m3 per household) a reduction inwater import of 34 can be achieved Increasing totalstorage volume increases the percentage water savingbut reduces the efficiency of the tank (Figure 10) Aneconomic analysis is required to determine a feasiblevolume for the cluster stormwater tanks and this inturn determines the potential for water saving ofthis strategy Saving more than 5 by stormwaterharvesting is estimated to be very unlikely

B Rainwater harvesting

This strategy is more effective than strategy A in termsof overall water savings in the city and also moreefficient in terms of the volume of water saved per unit

rainwater tank volume (Figure 10) This difference iscaused by the higher quality of the rainwater whichallows (in this study) use for all household purposesFor a tank of 330 L per household the collectedrainwater is used for 32 and spilled from the tank for68 In strategy A the quality of the stormwater onlyallows use for toilet flushing and it is therefore mostlyspilled from the storage tanks during storm events (peryear 8 usage 92 spillage for the case with 033 m3

tank volume per household) In addition stormwaterin strategy A is in fact hardly used for irrigation sincethe storm events take place outside the irrigationseason Assuming that it is economical feasible toinstall a rainwater tank volume of about 075 m3 perhousehold then a total saving of 10 of water importsinto the city is possible Rozos et al (forthcoming)calculated that a 10 reduction of potable waterdemand in households in a Mediterranean climatewould increase the capital cost of the water supplysystem with about 40 while a 20 reduction in

Figure 8 The energy consuming components of Tel Avivrsquos water system

Figure 9 Energy use intensity of water and wastewater services by city (For Tel Aviv without energy consumption for theconveyance of effluent to irrigation areas in the Negev)Source Kenway et al (2008) SWITCH unpublished data

Urban Water Journal 113

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demand would be achievable when accepting a 160cost increase (ie even larger storage tanks)

C Permeable pavement

The surface of Tel Aviv is for 30 permeable and 70impermeable according to the calculated and esti-mated physical characteristics of the city (Tables 3and 4) The impermeable surface consists for 33 ofroads and pavements which could be made permeableby application of permeable types of pavementsAssuming that 80 of the roads and pavements canbe made permeable then the total impermeablesurface has been reduced by 26 Simulation withthe model showed that this would result in a reductionin stormwater generation of 20 (from 177 to 141MCM per year) The reduction in stormwater genera-tion is not only due to increased infiltration becausethe model simulates infiltration to increase onlyfrom 23 to 38 MCM per year The rest of thestormwater evaporates from the soil moisture storeand overflows via pervious surface runoff into thedrainage system

The purpose of this strategy would be to increaseaquifer recharge to allow more aquifer abstractionThe extra volume of abstraction per m2 of made-permeable pavement is about 02 m3m2 per yearA financial analysis will most likely show thatthis strategy is not feasible from a financial pointof view

D Wastewater reuse at unit-block scale

The model simulated grey wastewater treatmentstorage and reuse at household scale The storage

tank volumes based on the AquaCycle optimisationroutine resulted in a 21 reduced demand forimported water (99 MCM ) and a 27 reduction inwastewater flows from the city (94 MCM) Spillagefrom the tanks was small and therefore doubling thetank volumes changed the savings to 23 and 29 onlyrespectively Benefits of this strategy are reduced totaldemand which reduces the need for seawater desalina-tion and cost savings for wastewater collection andtreatment Costs of this strategy include costs forthe household-scale treatment and reuse system andthe reduction in effluent availability for agriculturein the Negev Potential health risks from wastewaterstorage and treatment at household and from potentialcross connections in double distribution networksshould also be addressed

E Wastewater reuse at cluster scale

The model simulated grey wastewater treatment andstorage at cluster level and reuse for toilet flushingirrigation of gardens and irrigation of open publicspace The storage tank volumes based on theAquaCycle optimisation routine resulted in a 25reduced demand for imported water (115 MCM )and a 31 reduction in wastewater flows from thecity (108 MCM) Doubling the tank volumeschanged the savings to 32 and 40 respectivelyThe saving of imported water per unit volumestorage tank for the smaller (021 m3household)and larger (042 m3 per household) tanks were 300and 194 m3m3 per year respectively Comparingthese figures to stormwater strategies A and B(Figure 10) clearly shows that wastewater reuse hasmore potential to save imported water and requires

Figure 10 Potential for yearly water saving by implementation of strategies A and B (for the 2009 population and averageclimatic conditions of 1994ndash2007)

114 TTH Duong et al

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ded

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ober

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4

smaller tanks Reason for this difference is thatwastewater supply to the storage tanks is much lessfluctuating than stormwater flows

36 Evaluation of strategies under scenarios till2050 ndash demand for imported water (Indicator 5)

The demand for imported water in the city under thebaseline scenario increases from 472 MCM in 2009 to759 MCM in 2050 (Figure 11) due to populationgrowth The other scenarios slightly increase thedemand for imported water (778 MCM in 2050 forthe extreme scenario) The effect of climate change issmaller than one would maybe expect because thereduction in rainfall in the wet season does not increasethe demand for irrigation water since that demand isthere only in the dry season The increase intemperature during the dry season increases the

evapotranspiration and demand for irrigation waterbut only to a limited extend

The volume of water saved by the differentstrategies is constant with time for the lsquobaselinersquo andlsquono major changersquo scenarios but is affected by thechange in precipitation and temperature in the otherscenarios The volume of water saved by the strategy B(rainwater harvesting) will be less under the latterscenarios because the rainfall is less Figure 11 alsoshows that the volume of water saved in that strategyfluctuates from year to year with the fluctuations inyearly rainfall

The timing of the implementation of the strategiescould be based on keeping the total demand forimported water under a certain level Figure 12 showshow implementation of strategies B and D partlycancels the increase in demand due to populationgrowth

Figure 12 The simulated import of fresh water into Tel Aviv until 2050 based on phased implementation of strategies B and Dunder lsquonormalrsquo and lsquoextremersquo scenarios

Figure 11 The simulated import of fresh water into Tel Aviv until 2050 based on the lsquonormalrsquo scenario and different strategiesEmpirical data for 1996ndash2006 is also shown (source TahalMunicipality of Tel Aviv)

Urban Water Journal 115

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37 Evaluation of strategies under scenarios till2050 ndash other indicators

Energy consumption per volume of water consumedcould be reduced by various measures such asreduction of physical leakage (Colombo et al 2002)or by optimising pump technology and pumpingschedules Energy consumption of the alternativestrategies was calculated to investigate their effecton the nexus water ndash energy The energy consumptionin the whole urban water system (Table 6) per m3

of water used (imported thorn reused water) in the citywas on average 289 kWh per m3 for the period2009ndash2050 (baseline scenario) Implementation of thestrategies affected the energy consumption in differentways Strategy B with a 330-L tank per householdresults in 274 kWhm3 mainly because rainwatersystems are estimated to use 0278 KWhm3 (Kenwayet al 2008) which is less energy intensive thenimporting water Wastewater treatment and reuse atcluster scale (strategy E 210-L tank per household)reduces energy consumption to 245 kWhm3 but thesame strategy at household (strategy D 200-L tankper household in cluster 1 2 3 5 6 and 100 L incluster 4) scale increases energy consumption till 318kWhm3 This is due to the higher energy con-sumption for on-site wastewater treatment systems(4 kWhm3 Steendam 2009) than for small waste-water treatment plants (estimated as 08 kWhm3

based on a reported range of 039 to 117 kWhm3 by

Young and Koopman 1991) Therefore it seems thatstrategy D performs best for both saving water andsaving energy

Implementation of the strategies will clearly affectsome of the indicators (Table 2 indicators 5 6 7 810) while other indicators are conditions for successfulimplementation (indicators 1 2 4 6) rather thanresults and yet other indicators are not likely to beaffected (indicators 11 12 13) The effect of thestrategies on groundwater quality and receiving surfacewater quality (indicator 9) is unsure and the topic ofongoing investigations

4 Conclusions

Based on the investigation of Tel Avivrsquos urban watersystem and the simulation results of AquaCyclefollowing conclusions are drawn

The volume of water imported into the city (onaverage 47 MCM per year) and the seasonalfluctuations in the period 2003ndash2007 was accu-rately described by the AquaCycle model usingthe input files on climate physical characteristicsof the city surface and average figures fordomestic end-use categories

Evaluation of several strategies to improve thesustainability of the water system showedthat rainwater harvesting from roofs for non-

Table 6 Energy consumption inventory of Tel Avivrsquos water system

Energy consumption(KWhm3)

Proportion oftotal amount

of water Source of data

Pumping water from the Lake ofGalilee to the city

13 90 Mekorot Company

Treating water from the Lake of Galilee 0 100 Mekorot Company(negligible since supplied toconsumer without treatment)

Treating amp pumping Sea water 39 2 Mekorot CompanyPumping groundwater from local wells 0371 8 Tel Aviv MunicipalityTreating groundwater from local wells 0 8 Tel Aviv Municipality

(negligible since supplied toconsumer without treatment)

Pumping for distributing water ndash North area 0103 135 Tel Aviv MunicipalityPumping for distributing water ndash South area 0077 72 Tel Aviv MunicipalityHeating water at household 407 27 EstimationWastewater collection 0111 100 Tel Aviv MunicipalityWastewater treatment 0425 100 Mekorot CompanyPumping treated wastewater for irrigation 145 100 Mekorot CompanyPumping stormwater 0 100 Tel Aviv Municipality

(negligible since dischargeddirectly to the Sea by gravity)

Total ( including heating water at household) 1427Total (not including household heating water ) 328

It was assumed that all water supplied by Mekorot to the city was taken from the Lake of Galilee rather than from groundwater pumpingstations closer to the city (such as Rosh HaAyin)

Based on 1 m3 supplied collected treated and reused

116 TTH Duong et al

Dow

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ded

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Uni

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ity o

f C

hica

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ibra

ry]

at 1

243

11

Oct

ober

201

4

potable reuse in households is more promisingthan stormwater collection and reuse at clusterscale Assuming that it is feasible to install arainwater tank volume of about 075 m3 perhousehold then a total saving of 10 of waterimports into the city is possible

The overall water mass balance for the cityshowed that this rainwater harvesting strategywould reduce the amount of stormwater thatleaves the city per year from 22 MCM toabout 17 MCM which shows that othertechnologies or approaches are necessary ifone would like to make full beneficial use ofthis resource

Increasing rainwater infiltration for aquiferrecharge is most likely not financially sustainablesince the extra volume of recharge to allow moreaquifer abstraction is only 02 m3year per m2 ofmade-permeable pavement

The largest saving of water imports could beachieved by wastewater reuse for urban non-potable uses Wastewater collection storage(042 m3 per household) treatment and reuse atcluster scale is simulated to result in a 32 and40 reduction in water imports and wastewaterflows respectively

The most important factor of future scenariosfor water demand is population growth Effectsof climate change (reduced rainfall to a max-imum of 30 and increase in temperature to amaximum of 258C) on imported water weremuch smaller not more than 25 increase inthe extreme scenario This is in agreement withRozos et al (forthcoming) who have estimatedfor a Mediterranean climate an increase between0 and 4 depending on the capacity of therainwater harvesting scheme

Energy consumption in the urban water systemwas calculated as 289 kWh per m3 of volume ofwater used (import thorn reuse) in the city forthe period 2009ndash2050 Implementation of thestrategies affects the energy consumption indifferent ways Rainwater harvesting has somepotential to reduce energy consumption (to 274kWh per m3) but the best strategy in thisrespect is wastewater treatment and reuse atcluster scale (245 kWh per m3) The samestrategy at household scale causes an increasein energy consumption (318 kWh per m3)

The results of the model and the scenarioplanning study can be used to score a numberof the suggested sustainability indicators for theurban water system of Tel Aviv and as such canbe used by the multidisciplinary Water Club tosteer the city towards sustainability

Acknowledgements

The authors would like to thank the Dutch governmentfor its support through the NPT programme andthe European Commission for its support through theSWITCH project (FP6 Global Change and Ecosystems018530)

References

Butterworth JA Sutherland A Manning N Darteh BDziegielewska-Geitz M Eckart J Batchelor CMoriarty P Schouten T Da Silva C Verhagen Jand Bury PJ 2008 Building more effective partnershipsfor innovation in urban water management In Interna-tional Conference on Water and Urban DevelopmentParadigms Towards an integration of engineering designand management approaches 15ndash19 September 2008Katholieke Universiteit Leuven Belgium

Cities Alliance 2006 Guide to City Development StrategiesImproving urban performance Washington DC USApp 92

Colombo AF and Karney BW 2002 Energy and costs ofleaky pipes Toward comprehensive picture ASCEJournal of Water Resources Planning and Management128 (6) 441ndash450

ECAampD (European Climate Assessment amp Dataset Project)2008 Data records httpecaknminl [AccessedApril 2010]

Israel Ministry of Environmental Protection 2008 Israelrsquosadaption to climate change ndash Impacts and recommenda-tion httpwwwsvivagovil [Accessed April 2010]

Karka P Manoli E Lekkas DF and AssimacopoulosD 2007 A case study on integrated urban watermodelling using aquacyle In Proceedings of the 10thInternational Conference on Environmental Science ampTechnology Kos Island Greece 5ndash7 September 2007

Kenway SJ Priestley A Cook S Seo S Inman MGregory A and Hall M 2008 Energy use in theprovision and consumption of urban water in Australiaamp New Zealand Water for a Healthy country Flagshipreport series ISSN 1835ndash095X Water Service Associa-tion of Australia

Lundin M 2003 Indicators for measuring the sustainabilityof urban water system ndash A life cycle approach PhDdissertation Chalmers University of Technology

Makropoulos CK Memon FA Shirley-Smith C andButler D 2008a Futures An exploration of scenariosfor sustainable urban water management Water Policy10 345ndash373

Makropoulos CK Natsis K Liu S Mittas K andButler D 2008b Decision support for sustainableoption selection in integrated urban water managementEnvironmental Modelling amp Software 23 (12) 1448ndash1460

Mitchell V 2005 AquaCycle user guide A daily urban waterbalance model Australia Monash University Press

Mitchell V 2006 Applying integrated urban water manage-ment concepts A review of Australian experienceEnvironmental Management 37 (5) 589ndash605

Mitchell V Mein RG and McMahon TA 2001Modelling the urban water cycle Environmental Model-ling amp Software 16 615ndash629

Municipality of Tel Aviv 2006 City ndash The Strategic plan forTel Aviv Yafo Strategic Planning Unit Tel AvivMunicipality Israel

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demand would be achievable when accepting a 160cost increase (ie even larger storage tanks)

C Permeable pavement

The surface of Tel Aviv is for 30 permeable and 70impermeable according to the calculated and esti-mated physical characteristics of the city (Tables 3and 4) The impermeable surface consists for 33 ofroads and pavements which could be made permeableby application of permeable types of pavementsAssuming that 80 of the roads and pavements canbe made permeable then the total impermeablesurface has been reduced by 26 Simulation withthe model showed that this would result in a reductionin stormwater generation of 20 (from 177 to 141MCM per year) The reduction in stormwater genera-tion is not only due to increased infiltration becausethe model simulates infiltration to increase onlyfrom 23 to 38 MCM per year The rest of thestormwater evaporates from the soil moisture storeand overflows via pervious surface runoff into thedrainage system

The purpose of this strategy would be to increaseaquifer recharge to allow more aquifer abstractionThe extra volume of abstraction per m2 of made-permeable pavement is about 02 m3m2 per yearA financial analysis will most likely show thatthis strategy is not feasible from a financial pointof view

D Wastewater reuse at unit-block scale

The model simulated grey wastewater treatmentstorage and reuse at household scale The storage

tank volumes based on the AquaCycle optimisationroutine resulted in a 21 reduced demand forimported water (99 MCM ) and a 27 reduction inwastewater flows from the city (94 MCM) Spillagefrom the tanks was small and therefore doubling thetank volumes changed the savings to 23 and 29 onlyrespectively Benefits of this strategy are reduced totaldemand which reduces the need for seawater desalina-tion and cost savings for wastewater collection andtreatment Costs of this strategy include costs forthe household-scale treatment and reuse system andthe reduction in effluent availability for agriculturein the Negev Potential health risks from wastewaterstorage and treatment at household and from potentialcross connections in double distribution networksshould also be addressed

E Wastewater reuse at cluster scale

The model simulated grey wastewater treatment andstorage at cluster level and reuse for toilet flushingirrigation of gardens and irrigation of open publicspace The storage tank volumes based on theAquaCycle optimisation routine resulted in a 25reduced demand for imported water (115 MCM )and a 31 reduction in wastewater flows from thecity (108 MCM) Doubling the tank volumeschanged the savings to 32 and 40 respectivelyThe saving of imported water per unit volumestorage tank for the smaller (021 m3household)and larger (042 m3 per household) tanks were 300and 194 m3m3 per year respectively Comparingthese figures to stormwater strategies A and B(Figure 10) clearly shows that wastewater reuse hasmore potential to save imported water and requires

Figure 10 Potential for yearly water saving by implementation of strategies A and B (for the 2009 population and averageclimatic conditions of 1994ndash2007)

114 TTH Duong et al

Dow

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ded

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ity o

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ry]

at 1

243

11

Oct

ober

201

4

smaller tanks Reason for this difference is thatwastewater supply to the storage tanks is much lessfluctuating than stormwater flows

36 Evaluation of strategies under scenarios till2050 ndash demand for imported water (Indicator 5)

The demand for imported water in the city under thebaseline scenario increases from 472 MCM in 2009 to759 MCM in 2050 (Figure 11) due to populationgrowth The other scenarios slightly increase thedemand for imported water (778 MCM in 2050 forthe extreme scenario) The effect of climate change issmaller than one would maybe expect because thereduction in rainfall in the wet season does not increasethe demand for irrigation water since that demand isthere only in the dry season The increase intemperature during the dry season increases the

evapotranspiration and demand for irrigation waterbut only to a limited extend

The volume of water saved by the differentstrategies is constant with time for the lsquobaselinersquo andlsquono major changersquo scenarios but is affected by thechange in precipitation and temperature in the otherscenarios The volume of water saved by the strategy B(rainwater harvesting) will be less under the latterscenarios because the rainfall is less Figure 11 alsoshows that the volume of water saved in that strategyfluctuates from year to year with the fluctuations inyearly rainfall

The timing of the implementation of the strategiescould be based on keeping the total demand forimported water under a certain level Figure 12 showshow implementation of strategies B and D partlycancels the increase in demand due to populationgrowth

Figure 12 The simulated import of fresh water into Tel Aviv until 2050 based on phased implementation of strategies B and Dunder lsquonormalrsquo and lsquoextremersquo scenarios

Figure 11 The simulated import of fresh water into Tel Aviv until 2050 based on the lsquonormalrsquo scenario and different strategiesEmpirical data for 1996ndash2006 is also shown (source TahalMunicipality of Tel Aviv)

Urban Water Journal 115

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Oct

ober

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4

37 Evaluation of strategies under scenarios till2050 ndash other indicators

Energy consumption per volume of water consumedcould be reduced by various measures such asreduction of physical leakage (Colombo et al 2002)or by optimising pump technology and pumpingschedules Energy consumption of the alternativestrategies was calculated to investigate their effecton the nexus water ndash energy The energy consumptionin the whole urban water system (Table 6) per m3

of water used (imported thorn reused water) in the citywas on average 289 kWh per m3 for the period2009ndash2050 (baseline scenario) Implementation of thestrategies affected the energy consumption in differentways Strategy B with a 330-L tank per householdresults in 274 kWhm3 mainly because rainwatersystems are estimated to use 0278 KWhm3 (Kenwayet al 2008) which is less energy intensive thenimporting water Wastewater treatment and reuse atcluster scale (strategy E 210-L tank per household)reduces energy consumption to 245 kWhm3 but thesame strategy at household (strategy D 200-L tankper household in cluster 1 2 3 5 6 and 100 L incluster 4) scale increases energy consumption till 318kWhm3 This is due to the higher energy con-sumption for on-site wastewater treatment systems(4 kWhm3 Steendam 2009) than for small waste-water treatment plants (estimated as 08 kWhm3

based on a reported range of 039 to 117 kWhm3 by

Young and Koopman 1991) Therefore it seems thatstrategy D performs best for both saving water andsaving energy

Implementation of the strategies will clearly affectsome of the indicators (Table 2 indicators 5 6 7 810) while other indicators are conditions for successfulimplementation (indicators 1 2 4 6) rather thanresults and yet other indicators are not likely to beaffected (indicators 11 12 13) The effect of thestrategies on groundwater quality and receiving surfacewater quality (indicator 9) is unsure and the topic ofongoing investigations

4 Conclusions

Based on the investigation of Tel Avivrsquos urban watersystem and the simulation results of AquaCyclefollowing conclusions are drawn

The volume of water imported into the city (onaverage 47 MCM per year) and the seasonalfluctuations in the period 2003ndash2007 was accu-rately described by the AquaCycle model usingthe input files on climate physical characteristicsof the city surface and average figures fordomestic end-use categories

Evaluation of several strategies to improve thesustainability of the water system showedthat rainwater harvesting from roofs for non-

Table 6 Energy consumption inventory of Tel Avivrsquos water system

Energy consumption(KWhm3)

Proportion oftotal amount

of water Source of data

Pumping water from the Lake ofGalilee to the city

13 90 Mekorot Company

Treating water from the Lake of Galilee 0 100 Mekorot Company(negligible since supplied toconsumer without treatment)

Treating amp pumping Sea water 39 2 Mekorot CompanyPumping groundwater from local wells 0371 8 Tel Aviv MunicipalityTreating groundwater from local wells 0 8 Tel Aviv Municipality

(negligible since supplied toconsumer without treatment)

Pumping for distributing water ndash North area 0103 135 Tel Aviv MunicipalityPumping for distributing water ndash South area 0077 72 Tel Aviv MunicipalityHeating water at household 407 27 EstimationWastewater collection 0111 100 Tel Aviv MunicipalityWastewater treatment 0425 100 Mekorot CompanyPumping treated wastewater for irrigation 145 100 Mekorot CompanyPumping stormwater 0 100 Tel Aviv Municipality

(negligible since dischargeddirectly to the Sea by gravity)

Total ( including heating water at household) 1427Total (not including household heating water ) 328

It was assumed that all water supplied by Mekorot to the city was taken from the Lake of Galilee rather than from groundwater pumpingstations closer to the city (such as Rosh HaAyin)

Based on 1 m3 supplied collected treated and reused

116 TTH Duong et al

Dow

nloa

ded

by [

Uni

vers

ity o

f C

hica

go L

ibra

ry]

at 1

243

11

Oct

ober

201

4

potable reuse in households is more promisingthan stormwater collection and reuse at clusterscale Assuming that it is feasible to install arainwater tank volume of about 075 m3 perhousehold then a total saving of 10 of waterimports into the city is possible

The overall water mass balance for the cityshowed that this rainwater harvesting strategywould reduce the amount of stormwater thatleaves the city per year from 22 MCM toabout 17 MCM which shows that othertechnologies or approaches are necessary ifone would like to make full beneficial use ofthis resource

Increasing rainwater infiltration for aquiferrecharge is most likely not financially sustainablesince the extra volume of recharge to allow moreaquifer abstraction is only 02 m3year per m2 ofmade-permeable pavement

The largest saving of water imports could beachieved by wastewater reuse for urban non-potable uses Wastewater collection storage(042 m3 per household) treatment and reuse atcluster scale is simulated to result in a 32 and40 reduction in water imports and wastewaterflows respectively

The most important factor of future scenariosfor water demand is population growth Effectsof climate change (reduced rainfall to a max-imum of 30 and increase in temperature to amaximum of 258C) on imported water weremuch smaller not more than 25 increase inthe extreme scenario This is in agreement withRozos et al (forthcoming) who have estimatedfor a Mediterranean climate an increase between0 and 4 depending on the capacity of therainwater harvesting scheme

Energy consumption in the urban water systemwas calculated as 289 kWh per m3 of volume ofwater used (import thorn reuse) in the city forthe period 2009ndash2050 Implementation of thestrategies affects the energy consumption indifferent ways Rainwater harvesting has somepotential to reduce energy consumption (to 274kWh per m3) but the best strategy in thisrespect is wastewater treatment and reuse atcluster scale (245 kWh per m3) The samestrategy at household scale causes an increasein energy consumption (318 kWh per m3)

The results of the model and the scenarioplanning study can be used to score a numberof the suggested sustainability indicators for theurban water system of Tel Aviv and as such canbe used by the multidisciplinary Water Club tosteer the city towards sustainability

Acknowledgements

The authors would like to thank the Dutch governmentfor its support through the NPT programme andthe European Commission for its support through theSWITCH project (FP6 Global Change and Ecosystems018530)

References

Butterworth JA Sutherland A Manning N Darteh BDziegielewska-Geitz M Eckart J Batchelor CMoriarty P Schouten T Da Silva C Verhagen Jand Bury PJ 2008 Building more effective partnershipsfor innovation in urban water management In Interna-tional Conference on Water and Urban DevelopmentParadigms Towards an integration of engineering designand management approaches 15ndash19 September 2008Katholieke Universiteit Leuven Belgium

Cities Alliance 2006 Guide to City Development StrategiesImproving urban performance Washington DC USApp 92

Colombo AF and Karney BW 2002 Energy and costs ofleaky pipes Toward comprehensive picture ASCEJournal of Water Resources Planning and Management128 (6) 441ndash450

ECAampD (European Climate Assessment amp Dataset Project)2008 Data records httpecaknminl [AccessedApril 2010]

Israel Ministry of Environmental Protection 2008 Israelrsquosadaption to climate change ndash Impacts and recommenda-tion httpwwwsvivagovil [Accessed April 2010]

Karka P Manoli E Lekkas DF and AssimacopoulosD 2007 A case study on integrated urban watermodelling using aquacyle In Proceedings of the 10thInternational Conference on Environmental Science ampTechnology Kos Island Greece 5ndash7 September 2007

Kenway SJ Priestley A Cook S Seo S Inman MGregory A and Hall M 2008 Energy use in theprovision and consumption of urban water in Australiaamp New Zealand Water for a Healthy country Flagshipreport series ISSN 1835ndash095X Water Service Associa-tion of Australia

Lundin M 2003 Indicators for measuring the sustainabilityof urban water system ndash A life cycle approach PhDdissertation Chalmers University of Technology

Makropoulos CK Memon FA Shirley-Smith C andButler D 2008a Futures An exploration of scenariosfor sustainable urban water management Water Policy10 345ndash373

Makropoulos CK Natsis K Liu S Mittas K andButler D 2008b Decision support for sustainableoption selection in integrated urban water managementEnvironmental Modelling amp Software 23 (12) 1448ndash1460

Mitchell V 2005 AquaCycle user guide A daily urban waterbalance model Australia Monash University Press

Mitchell V 2006 Applying integrated urban water manage-ment concepts A review of Australian experienceEnvironmental Management 37 (5) 589ndash605

Mitchell V Mein RG and McMahon TA 2001Modelling the urban water cycle Environmental Model-ling amp Software 16 615ndash629

Municipality of Tel Aviv 2006 City ndash The Strategic plan forTel Aviv Yafo Strategic Planning Unit Tel AvivMunicipality Israel

Urban Water Journal 117

Dow

nloa

ded

by [

Uni

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f C

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ibra

ry]

at 1

243

11

Oct

ober

201

4

smaller tanks Reason for this difference is thatwastewater supply to the storage tanks is much lessfluctuating than stormwater flows

36 Evaluation of strategies under scenarios till2050 ndash demand for imported water (Indicator 5)

The demand for imported water in the city under thebaseline scenario increases from 472 MCM in 2009 to759 MCM in 2050 (Figure 11) due to populationgrowth The other scenarios slightly increase thedemand for imported water (778 MCM in 2050 forthe extreme scenario) The effect of climate change issmaller than one would maybe expect because thereduction in rainfall in the wet season does not increasethe demand for irrigation water since that demand isthere only in the dry season The increase intemperature during the dry season increases the

evapotranspiration and demand for irrigation waterbut only to a limited extend

The volume of water saved by the differentstrategies is constant with time for the lsquobaselinersquo andlsquono major changersquo scenarios but is affected by thechange in precipitation and temperature in the otherscenarios The volume of water saved by the strategy B(rainwater harvesting) will be less under the latterscenarios because the rainfall is less Figure 11 alsoshows that the volume of water saved in that strategyfluctuates from year to year with the fluctuations inyearly rainfall

The timing of the implementation of the strategiescould be based on keeping the total demand forimported water under a certain level Figure 12 showshow implementation of strategies B and D partlycancels the increase in demand due to populationgrowth

Figure 12 The simulated import of fresh water into Tel Aviv until 2050 based on phased implementation of strategies B and Dunder lsquonormalrsquo and lsquoextremersquo scenarios

Figure 11 The simulated import of fresh water into Tel Aviv until 2050 based on the lsquonormalrsquo scenario and different strategiesEmpirical data for 1996ndash2006 is also shown (source TahalMunicipality of Tel Aviv)

Urban Water Journal 115

Dow

nloa

ded

by [

Uni

vers

ity o

f C

hica

go L

ibra

ry]

at 1

243

11

Oct

ober

201

4

37 Evaluation of strategies under scenarios till2050 ndash other indicators

Energy consumption per volume of water consumedcould be reduced by various measures such asreduction of physical leakage (Colombo et al 2002)or by optimising pump technology and pumpingschedules Energy consumption of the alternativestrategies was calculated to investigate their effecton the nexus water ndash energy The energy consumptionin the whole urban water system (Table 6) per m3

of water used (imported thorn reused water) in the citywas on average 289 kWh per m3 for the period2009ndash2050 (baseline scenario) Implementation of thestrategies affected the energy consumption in differentways Strategy B with a 330-L tank per householdresults in 274 kWhm3 mainly because rainwatersystems are estimated to use 0278 KWhm3 (Kenwayet al 2008) which is less energy intensive thenimporting water Wastewater treatment and reuse atcluster scale (strategy E 210-L tank per household)reduces energy consumption to 245 kWhm3 but thesame strategy at household (strategy D 200-L tankper household in cluster 1 2 3 5 6 and 100 L incluster 4) scale increases energy consumption till 318kWhm3 This is due to the higher energy con-sumption for on-site wastewater treatment systems(4 kWhm3 Steendam 2009) than for small waste-water treatment plants (estimated as 08 kWhm3

based on a reported range of 039 to 117 kWhm3 by

Young and Koopman 1991) Therefore it seems thatstrategy D performs best for both saving water andsaving energy

Implementation of the strategies will clearly affectsome of the indicators (Table 2 indicators 5 6 7 810) while other indicators are conditions for successfulimplementation (indicators 1 2 4 6) rather thanresults and yet other indicators are not likely to beaffected (indicators 11 12 13) The effect of thestrategies on groundwater quality and receiving surfacewater quality (indicator 9) is unsure and the topic ofongoing investigations

4 Conclusions

Based on the investigation of Tel Avivrsquos urban watersystem and the simulation results of AquaCyclefollowing conclusions are drawn

The volume of water imported into the city (onaverage 47 MCM per year) and the seasonalfluctuations in the period 2003ndash2007 was accu-rately described by the AquaCycle model usingthe input files on climate physical characteristicsof the city surface and average figures fordomestic end-use categories

Evaluation of several strategies to improve thesustainability of the water system showedthat rainwater harvesting from roofs for non-

Table 6 Energy consumption inventory of Tel Avivrsquos water system

Energy consumption(KWhm3)

Proportion oftotal amount

of water Source of data

Pumping water from the Lake ofGalilee to the city

13 90 Mekorot Company

Treating water from the Lake of Galilee 0 100 Mekorot Company(negligible since supplied toconsumer without treatment)

Treating amp pumping Sea water 39 2 Mekorot CompanyPumping groundwater from local wells 0371 8 Tel Aviv MunicipalityTreating groundwater from local wells 0 8 Tel Aviv Municipality

(negligible since supplied toconsumer without treatment)

Pumping for distributing water ndash North area 0103 135 Tel Aviv MunicipalityPumping for distributing water ndash South area 0077 72 Tel Aviv MunicipalityHeating water at household 407 27 EstimationWastewater collection 0111 100 Tel Aviv MunicipalityWastewater treatment 0425 100 Mekorot CompanyPumping treated wastewater for irrigation 145 100 Mekorot CompanyPumping stormwater 0 100 Tel Aviv Municipality

(negligible since dischargeddirectly to the Sea by gravity)

Total ( including heating water at household) 1427Total (not including household heating water ) 328

It was assumed that all water supplied by Mekorot to the city was taken from the Lake of Galilee rather than from groundwater pumpingstations closer to the city (such as Rosh HaAyin)

Based on 1 m3 supplied collected treated and reused

116 TTH Duong et al

Dow

nloa

ded

by [

Uni

vers

ity o

f C

hica

go L

ibra

ry]

at 1

243

11

Oct

ober

201

4

potable reuse in households is more promisingthan stormwater collection and reuse at clusterscale Assuming that it is feasible to install arainwater tank volume of about 075 m3 perhousehold then a total saving of 10 of waterimports into the city is possible

The overall water mass balance for the cityshowed that this rainwater harvesting strategywould reduce the amount of stormwater thatleaves the city per year from 22 MCM toabout 17 MCM which shows that othertechnologies or approaches are necessary ifone would like to make full beneficial use ofthis resource

Increasing rainwater infiltration for aquiferrecharge is most likely not financially sustainablesince the extra volume of recharge to allow moreaquifer abstraction is only 02 m3year per m2 ofmade-permeable pavement

The largest saving of water imports could beachieved by wastewater reuse for urban non-potable uses Wastewater collection storage(042 m3 per household) treatment and reuse atcluster scale is simulated to result in a 32 and40 reduction in water imports and wastewaterflows respectively

The most important factor of future scenariosfor water demand is population growth Effectsof climate change (reduced rainfall to a max-imum of 30 and increase in temperature to amaximum of 258C) on imported water weremuch smaller not more than 25 increase inthe extreme scenario This is in agreement withRozos et al (forthcoming) who have estimatedfor a Mediterranean climate an increase between0 and 4 depending on the capacity of therainwater harvesting scheme

Energy consumption in the urban water systemwas calculated as 289 kWh per m3 of volume ofwater used (import thorn reuse) in the city forthe period 2009ndash2050 Implementation of thestrategies affects the energy consumption indifferent ways Rainwater harvesting has somepotential to reduce energy consumption (to 274kWh per m3) but the best strategy in thisrespect is wastewater treatment and reuse atcluster scale (245 kWh per m3) The samestrategy at household scale causes an increasein energy consumption (318 kWh per m3)

The results of the model and the scenarioplanning study can be used to score a numberof the suggested sustainability indicators for theurban water system of Tel Aviv and as such canbe used by the multidisciplinary Water Club tosteer the city towards sustainability

Acknowledgements

The authors would like to thank the Dutch governmentfor its support through the NPT programme andthe European Commission for its support through theSWITCH project (FP6 Global Change and Ecosystems018530)

References

Butterworth JA Sutherland A Manning N Darteh BDziegielewska-Geitz M Eckart J Batchelor CMoriarty P Schouten T Da Silva C Verhagen Jand Bury PJ 2008 Building more effective partnershipsfor innovation in urban water management In Interna-tional Conference on Water and Urban DevelopmentParadigms Towards an integration of engineering designand management approaches 15ndash19 September 2008Katholieke Universiteit Leuven Belgium

Cities Alliance 2006 Guide to City Development StrategiesImproving urban performance Washington DC USApp 92

Colombo AF and Karney BW 2002 Energy and costs ofleaky pipes Toward comprehensive picture ASCEJournal of Water Resources Planning and Management128 (6) 441ndash450

ECAampD (European Climate Assessment amp Dataset Project)2008 Data records httpecaknminl [AccessedApril 2010]

Israel Ministry of Environmental Protection 2008 Israelrsquosadaption to climate change ndash Impacts and recommenda-tion httpwwwsvivagovil [Accessed April 2010]

Karka P Manoli E Lekkas DF and AssimacopoulosD 2007 A case study on integrated urban watermodelling using aquacyle In Proceedings of the 10thInternational Conference on Environmental Science ampTechnology Kos Island Greece 5ndash7 September 2007

Kenway SJ Priestley A Cook S Seo S Inman MGregory A and Hall M 2008 Energy use in theprovision and consumption of urban water in Australiaamp New Zealand Water for a Healthy country Flagshipreport series ISSN 1835ndash095X Water Service Associa-tion of Australia

Lundin M 2003 Indicators for measuring the sustainabilityof urban water system ndash A life cycle approach PhDdissertation Chalmers University of Technology

Makropoulos CK Memon FA Shirley-Smith C andButler D 2008a Futures An exploration of scenariosfor sustainable urban water management Water Policy10 345ndash373

Makropoulos CK Natsis K Liu S Mittas K andButler D 2008b Decision support for sustainableoption selection in integrated urban water managementEnvironmental Modelling amp Software 23 (12) 1448ndash1460

Mitchell V 2005 AquaCycle user guide A daily urban waterbalance model Australia Monash University Press

Mitchell V 2006 Applying integrated urban water manage-ment concepts A review of Australian experienceEnvironmental Management 37 (5) 589ndash605

Mitchell V Mein RG and McMahon TA 2001Modelling the urban water cycle Environmental Model-ling amp Software 16 615ndash629

Municipality of Tel Aviv 2006 City ndash The Strategic plan forTel Aviv Yafo Strategic Planning Unit Tel AvivMunicipality Israel

Urban Water Journal 117

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37 Evaluation of strategies under scenarios till2050 ndash other indicators

Energy consumption per volume of water consumedcould be reduced by various measures such asreduction of physical leakage (Colombo et al 2002)or by optimising pump technology and pumpingschedules Energy consumption of the alternativestrategies was calculated to investigate their effecton the nexus water ndash energy The energy consumptionin the whole urban water system (Table 6) per m3

of water used (imported thorn reused water) in the citywas on average 289 kWh per m3 for the period2009ndash2050 (baseline scenario) Implementation of thestrategies affected the energy consumption in differentways Strategy B with a 330-L tank per householdresults in 274 kWhm3 mainly because rainwatersystems are estimated to use 0278 KWhm3 (Kenwayet al 2008) which is less energy intensive thenimporting water Wastewater treatment and reuse atcluster scale (strategy E 210-L tank per household)reduces energy consumption to 245 kWhm3 but thesame strategy at household (strategy D 200-L tankper household in cluster 1 2 3 5 6 and 100 L incluster 4) scale increases energy consumption till 318kWhm3 This is due to the higher energy con-sumption for on-site wastewater treatment systems(4 kWhm3 Steendam 2009) than for small waste-water treatment plants (estimated as 08 kWhm3

based on a reported range of 039 to 117 kWhm3 by

Young and Koopman 1991) Therefore it seems thatstrategy D performs best for both saving water andsaving energy

Implementation of the strategies will clearly affectsome of the indicators (Table 2 indicators 5 6 7 810) while other indicators are conditions for successfulimplementation (indicators 1 2 4 6) rather thanresults and yet other indicators are not likely to beaffected (indicators 11 12 13) The effect of thestrategies on groundwater quality and receiving surfacewater quality (indicator 9) is unsure and the topic ofongoing investigations

4 Conclusions

Based on the investigation of Tel Avivrsquos urban watersystem and the simulation results of AquaCyclefollowing conclusions are drawn

The volume of water imported into the city (onaverage 47 MCM per year) and the seasonalfluctuations in the period 2003ndash2007 was accu-rately described by the AquaCycle model usingthe input files on climate physical characteristicsof the city surface and average figures fordomestic end-use categories

Evaluation of several strategies to improve thesustainability of the water system showedthat rainwater harvesting from roofs for non-

Table 6 Energy consumption inventory of Tel Avivrsquos water system

Energy consumption(KWhm3)

Proportion oftotal amount

of water Source of data

Pumping water from the Lake ofGalilee to the city

13 90 Mekorot Company

Treating water from the Lake of Galilee 0 100 Mekorot Company(negligible since supplied toconsumer without treatment)

Treating amp pumping Sea water 39 2 Mekorot CompanyPumping groundwater from local wells 0371 8 Tel Aviv MunicipalityTreating groundwater from local wells 0 8 Tel Aviv Municipality

(negligible since supplied toconsumer without treatment)

Pumping for distributing water ndash North area 0103 135 Tel Aviv MunicipalityPumping for distributing water ndash South area 0077 72 Tel Aviv MunicipalityHeating water at household 407 27 EstimationWastewater collection 0111 100 Tel Aviv MunicipalityWastewater treatment 0425 100 Mekorot CompanyPumping treated wastewater for irrigation 145 100 Mekorot CompanyPumping stormwater 0 100 Tel Aviv Municipality

(negligible since dischargeddirectly to the Sea by gravity)

Total ( including heating water at household) 1427Total (not including household heating water ) 328

It was assumed that all water supplied by Mekorot to the city was taken from the Lake of Galilee rather than from groundwater pumpingstations closer to the city (such as Rosh HaAyin)

Based on 1 m3 supplied collected treated and reused

116 TTH Duong et al

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ober

201

4

potable reuse in households is more promisingthan stormwater collection and reuse at clusterscale Assuming that it is feasible to install arainwater tank volume of about 075 m3 perhousehold then a total saving of 10 of waterimports into the city is possible

The overall water mass balance for the cityshowed that this rainwater harvesting strategywould reduce the amount of stormwater thatleaves the city per year from 22 MCM toabout 17 MCM which shows that othertechnologies or approaches are necessary ifone would like to make full beneficial use ofthis resource

Increasing rainwater infiltration for aquiferrecharge is most likely not financially sustainablesince the extra volume of recharge to allow moreaquifer abstraction is only 02 m3year per m2 ofmade-permeable pavement

The largest saving of water imports could beachieved by wastewater reuse for urban non-potable uses Wastewater collection storage(042 m3 per household) treatment and reuse atcluster scale is simulated to result in a 32 and40 reduction in water imports and wastewaterflows respectively

The most important factor of future scenariosfor water demand is population growth Effectsof climate change (reduced rainfall to a max-imum of 30 and increase in temperature to amaximum of 258C) on imported water weremuch smaller not more than 25 increase inthe extreme scenario This is in agreement withRozos et al (forthcoming) who have estimatedfor a Mediterranean climate an increase between0 and 4 depending on the capacity of therainwater harvesting scheme

Energy consumption in the urban water systemwas calculated as 289 kWh per m3 of volume ofwater used (import thorn reuse) in the city forthe period 2009ndash2050 Implementation of thestrategies affects the energy consumption indifferent ways Rainwater harvesting has somepotential to reduce energy consumption (to 274kWh per m3) but the best strategy in thisrespect is wastewater treatment and reuse atcluster scale (245 kWh per m3) The samestrategy at household scale causes an increasein energy consumption (318 kWh per m3)

The results of the model and the scenarioplanning study can be used to score a numberof the suggested sustainability indicators for theurban water system of Tel Aviv and as such canbe used by the multidisciplinary Water Club tosteer the city towards sustainability

Acknowledgements

The authors would like to thank the Dutch governmentfor its support through the NPT programme andthe European Commission for its support through theSWITCH project (FP6 Global Change and Ecosystems018530)

References

Butterworth JA Sutherland A Manning N Darteh BDziegielewska-Geitz M Eckart J Batchelor CMoriarty P Schouten T Da Silva C Verhagen Jand Bury PJ 2008 Building more effective partnershipsfor innovation in urban water management In Interna-tional Conference on Water and Urban DevelopmentParadigms Towards an integration of engineering designand management approaches 15ndash19 September 2008Katholieke Universiteit Leuven Belgium

Cities Alliance 2006 Guide to City Development StrategiesImproving urban performance Washington DC USApp 92

Colombo AF and Karney BW 2002 Energy and costs ofleaky pipes Toward comprehensive picture ASCEJournal of Water Resources Planning and Management128 (6) 441ndash450

ECAampD (European Climate Assessment amp Dataset Project)2008 Data records httpecaknminl [AccessedApril 2010]

Israel Ministry of Environmental Protection 2008 Israelrsquosadaption to climate change ndash Impacts and recommenda-tion httpwwwsvivagovil [Accessed April 2010]

Karka P Manoli E Lekkas DF and AssimacopoulosD 2007 A case study on integrated urban watermodelling using aquacyle In Proceedings of the 10thInternational Conference on Environmental Science ampTechnology Kos Island Greece 5ndash7 September 2007

Kenway SJ Priestley A Cook S Seo S Inman MGregory A and Hall M 2008 Energy use in theprovision and consumption of urban water in Australiaamp New Zealand Water for a Healthy country Flagshipreport series ISSN 1835ndash095X Water Service Associa-tion of Australia

Lundin M 2003 Indicators for measuring the sustainabilityof urban water system ndash A life cycle approach PhDdissertation Chalmers University of Technology

Makropoulos CK Memon FA Shirley-Smith C andButler D 2008a Futures An exploration of scenariosfor sustainable urban water management Water Policy10 345ndash373

Makropoulos CK Natsis K Liu S Mittas K andButler D 2008b Decision support for sustainableoption selection in integrated urban water managementEnvironmental Modelling amp Software 23 (12) 1448ndash1460

Mitchell V 2005 AquaCycle user guide A daily urban waterbalance model Australia Monash University Press

Mitchell V 2006 Applying integrated urban water manage-ment concepts A review of Australian experienceEnvironmental Management 37 (5) 589ndash605

Mitchell V Mein RG and McMahon TA 2001Modelling the urban water cycle Environmental Model-ling amp Software 16 615ndash629

Municipality of Tel Aviv 2006 City ndash The Strategic plan forTel Aviv Yafo Strategic Planning Unit Tel AvivMunicipality Israel

Urban Water Journal 117

Dow

nloa

ded

by [

Uni

vers

ity o

f C

hica

go L

ibra

ry]

at 1

243

11

Oct

ober

201

4

potable reuse in households is more promisingthan stormwater collection and reuse at clusterscale Assuming that it is feasible to install arainwater tank volume of about 075 m3 perhousehold then a total saving of 10 of waterimports into the city is possible

The overall water mass balance for the cityshowed that this rainwater harvesting strategywould reduce the amount of stormwater thatleaves the city per year from 22 MCM toabout 17 MCM which shows that othertechnologies or approaches are necessary ifone would like to make full beneficial use ofthis resource

Increasing rainwater infiltration for aquiferrecharge is most likely not financially sustainablesince the extra volume of recharge to allow moreaquifer abstraction is only 02 m3year per m2 ofmade-permeable pavement

The largest saving of water imports could beachieved by wastewater reuse for urban non-potable uses Wastewater collection storage(042 m3 per household) treatment and reuse atcluster scale is simulated to result in a 32 and40 reduction in water imports and wastewaterflows respectively

The most important factor of future scenariosfor water demand is population growth Effectsof climate change (reduced rainfall to a max-imum of 30 and increase in temperature to amaximum of 258C) on imported water weremuch smaller not more than 25 increase inthe extreme scenario This is in agreement withRozos et al (forthcoming) who have estimatedfor a Mediterranean climate an increase between0 and 4 depending on the capacity of therainwater harvesting scheme

Energy consumption in the urban water systemwas calculated as 289 kWh per m3 of volume ofwater used (import thorn reuse) in the city forthe period 2009ndash2050 Implementation of thestrategies affects the energy consumption indifferent ways Rainwater harvesting has somepotential to reduce energy consumption (to 274kWh per m3) but the best strategy in thisrespect is wastewater treatment and reuse atcluster scale (245 kWh per m3) The samestrategy at household scale causes an increasein energy consumption (318 kWh per m3)

The results of the model and the scenarioplanning study can be used to score a numberof the suggested sustainability indicators for theurban water system of Tel Aviv and as such canbe used by the multidisciplinary Water Club tosteer the city towards sustainability

Acknowledgements

The authors would like to thank the Dutch governmentfor its support through the NPT programme andthe European Commission for its support through theSWITCH project (FP6 Global Change and Ecosystems018530)

References

Butterworth JA Sutherland A Manning N Darteh BDziegielewska-Geitz M Eckart J Batchelor CMoriarty P Schouten T Da Silva C Verhagen Jand Bury PJ 2008 Building more effective partnershipsfor innovation in urban water management In Interna-tional Conference on Water and Urban DevelopmentParadigms Towards an integration of engineering designand management approaches 15ndash19 September 2008Katholieke Universiteit Leuven Belgium

Cities Alliance 2006 Guide to City Development StrategiesImproving urban performance Washington DC USApp 92

Colombo AF and Karney BW 2002 Energy and costs ofleaky pipes Toward comprehensive picture ASCEJournal of Water Resources Planning and Management128 (6) 441ndash450

ECAampD (European Climate Assessment amp Dataset Project)2008 Data records httpecaknminl [AccessedApril 2010]

Israel Ministry of Environmental Protection 2008 Israelrsquosadaption to climate change ndash Impacts and recommenda-tion httpwwwsvivagovil [Accessed April 2010]

Karka P Manoli E Lekkas DF and AssimacopoulosD 2007 A case study on integrated urban watermodelling using aquacyle In Proceedings of the 10thInternational Conference on Environmental Science ampTechnology Kos Island Greece 5ndash7 September 2007

Kenway SJ Priestley A Cook S Seo S Inman MGregory A and Hall M 2008 Energy use in theprovision and consumption of urban water in Australiaamp New Zealand Water for a Healthy country Flagshipreport series ISSN 1835ndash095X Water Service Associa-tion of Australia

Lundin M 2003 Indicators for measuring the sustainabilityof urban water system ndash A life cycle approach PhDdissertation Chalmers University of Technology

Makropoulos CK Memon FA Shirley-Smith C andButler D 2008a Futures An exploration of scenariosfor sustainable urban water management Water Policy10 345ndash373

Makropoulos CK Natsis K Liu S Mittas K andButler D 2008b Decision support for sustainableoption selection in integrated urban water managementEnvironmental Modelling amp Software 23 (12) 1448ndash1460

Mitchell V 2005 AquaCycle user guide A daily urban waterbalance model Australia Monash University Press

Mitchell V 2006 Applying integrated urban water manage-ment concepts A review of Australian experienceEnvironmental Management 37 (5) 589ndash605

Mitchell V Mein RG and McMahon TA 2001Modelling the urban water cycle Environmental Model-ling amp Software 16 615ndash629

Municipality of Tel Aviv 2006 City ndash The Strategic plan forTel Aviv Yafo Strategic Planning Unit Tel AvivMunicipality Israel

Urban Water Journal 117

Dow

nloa

ded

by [

Uni

vers

ity o

f C

hica

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ry]

at 1

243

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Oct

ober

201

4

Rozos E Makropoulos C and Butler D forthcomingDesign robustness of local water-recycling schemesWater Resources Planning and Management ASCEhttpdxdoiorg101061(ASCE)WR1943-54520000067

Scheller A 2000 Measuring sustainability The making ofsustainability indicators in Interdisciplinary Researchsettings In 3th POSTI International Conference onPolicy Agendas for Sustainable Technological InnovationUnited Kingdom 1ndash3 December

Steendam R 2009 The effects of urban water managementoptions on the water balance and energy use in a newurban development (Haulender Weg) A field researchin Hamburg Germany MSC thesis MWI0902UNESCO-IHE Delft The Netherlands

SWITCH (EU Project ndash Sustainable Water Management inthe City of the Future) 2008 Switch approach to strategicplanning for integrated urban water managementSWITCH report httpwwwswitchurbanwatereu[Accessed April 2010]

Thornthwaite CW 1948 An approach toward a rationalclassification of climate Geographical Review (AmericanGeographical Society) 38 (1) 55ndash94

Van der Steen P and Howe C 2009 Managing water inthe city of the future strategic planning and scienceReviews in Environmental Science and Bio-Technology8 (2) 115ndash120

Young DF and Koopman B 1991 Electricity use in smallwastewater treatment plants Journal of EnvironmentalEngineering 117 (3) 300ndash307

White S and Turner A 2003 The role of effluent reuse insustainable urban water system Untapped opportunitiesIn National water recycling in Australia ConferenceBrisbane September 2003

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