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Matthew McCartney, Tadesse Alemayehu, Abeyu Shiferaw and Seleshi Bekele Awulachew
Evaluation of Current and Future Water Resources Development in the Lake Tana Basin, Ethiopia
134
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International Water Management InstituteP O Box 2075, Colombo, Sri Lanka
IWMI Research Report 134
Evaluation of Current and Future WaterResources Development in the Lake TanaBasin, Ethiopia
Matthew McCartney, Tadesse Alemayehu, Abeyu Shiferawand Seleshi Bekele Awulachew
ii
The authors: Matthew McCartney is a senior researcher specializing in hydrology andwater resource management at the subregional office for East Africa and the Nile Basin ofthe International Water Management Institute (IWMI) in Addis Ababa, Ethiopia (email:[email protected]); Tadesse Alemayehu was an independent consultant in AddisAbaba when this report was prepared and is now a lecturer at the University of Bahir Dar,Ethiopia. Abeyu Shiferaw was an independent consultant in Addis Ababa, Ethiopia whenthis report was prepared and is now the coordinator of an international Nuffic project onintegrated river basin management at Addis Ababa University; and Seleshi BekeleAwulachew is a senior researcher and the regional representative for the East Africa andNile Basin office of the International Water Management Institute in Addis Ababa, Ethiopia.
McCartney, M.; Alemayehu, T.; Shiferaw, A.; Awulachew, S. B. 2010. Evaluation of currentand future water resources development in the Lake Tana Basin, Ethiopia. Colombo, SriLanka: International Water Management Institute. 39p. (IWMI Research Report 134). doi:10.3910/2010. 204
/ water resources development / lakes / dams / environmental flows / hydrology /stakeholders / models / irrigation / hydropower / Ethiopia /
ISSN 1026-0862ISBN 978-92-9090-721-3
Copyright © 2010, by IWMI. All rights reserved. IWMI encourages the use of its materialprovided that the organization is acknowledged and kept informed in all such instances.
Cover photograph shows the shoreline of Lake Tana, Ethiopia (photo credit: MatthewMcCartney)
Please send inquiries and comments to: [email protected]
A free copy of this publication can be downloaded at
www.iwmi.org/Publications/IWMI_Research_Reports/index.aspx
iii
Acknowledgements
The authors would like to thank Ayalew Gebre and Derese Getachew of Addis Ababa University for theirassistance in conducting the stakeholder review. They are grateful to the Ethiopian Electric PowerCorporation, the Federal Ministry of Water Resources, the National Meteorological Agency and the CentralStatistical Agency of Ethiopia for the provision of data.
Project
This report presents findings from project number 36 entitled “ImprovedPlanning of Large Dam Operation: Using Decision Support Systems toOptimize Livelihood Benefits, Safeguard Health and Protect theEnvironment” of the CGIAR Challenge Program on Water and Food (CPWF).
The following organizations collaborated in the research conducted for this report.
International Water Management Institute, Addis Ababa, Ethiopia
Addis-Ababa University, Addis Ababa, Ethiopia
Southern Waters, Cape Town, South Africa
Water scarcity is one of the most pressing issues facing humanity today. The Challenge Program on Waterand Food (CPWF), an initiative of the Consultative Group on International Agricultural Research (CGIAR),contributes to efforts of the international community to ensure global diversions of water to agriculture aremaintained at the level of the year 2000. It is a multiinstitutional research initiative that aims to increasewater productivity for agriculture-that is, to change the way water is managed and used to meet internationalfood security and poverty eradication goals-and to leave more water for other users and the environment.
The CPWF deals with complex agriculture-related systems, for which there are a growing number ofstakeholders generating information. Its community-of-practice works in innovative ways to collate, unify,organize, extract, distill and share the ideas, information and knowledge to allow next-users to gain insightsand deduce principles, concepts and cause-and-effect relationships from its research results. To helpachieve this, the CPWF focuses on building multi-disciplinary north-south and south-south partnerships.
www.waterandfood.org
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Contents
Acronyms and Abbreviations vi
Summary vii
Introduction 1
The Study Area 2
Impacts of the Chara Chara Weir on Lake Tana Outflow and EnvironmentalFlow Assessment 6
Stakeholder Analysis of the Chara Chara Weir 15
Simulation of Future Water Resources Development 19
Discussion 26
Concluding Remarks 28
References 29
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Acronyms and Abbreviations
ARBWR Amhara Region - Bureau of Water Resources
BCEOM Egis Bceom International
BS Baseline Scenario
DRM Desktop Reserve Model
EEPCO Ethiopian Electric Power Corporation
EELPA Ethiopian Electricity Light and Power Authority
EIA Environmental Impact Assessment
EPLAUA Environmental Protection, Land Administration and Use Authority
EU European Union
FDS Full Development Scenario
LDS Likely Development Scenario
LTBRC Lake Tana Basin Research Centre
ODS Ongoing Development Scenario
PaDPA Amhara Parks Development and Protection Authority
TBF Tana Beles Flow
VEF Variable Environmental Flow
WEAP Water Evaluation And Planning (Model)
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adversely affected others. Future development willexacerbate pressure on the lake. If all the planneddevelopment occurs, the mean water level of thelake will drop by 0.44 meters (m), and the averagesurface area wil l decrease by 30 squarekilometers (km2) (i.e., 1%) and up to 81 km2 (i.e.,2.6%) during some dry seasons. There will beprolonged periods of several years during whichwater levels will be much lower than they wouldbe naturally. If environmental flow requirements(estimated to average 862 Mm3y-1) are maintainedin the reach containing the Tis Issat Waterfall, themean water level of the lake will reduce by a further0.37 m and the average lake area will reduce byan additional 26 km2. Without careful managementthese changes are likely to have severe ecologicaland social consequences. Hard choices must bemade about how the water is best utilized. It isimportant that all stakeholders, including localpeople, are involved in the decision-makingprocess and benefit from investments.
Summary
Lake Tana is valuable for many people, includingthe communities who live around the lakeshore,those living on islands and close to the Blue NileRiver, which flows from it. The area has beenidentified as a region for irrigation and hydropowerdevelopment, which are vital for food security andeconomic growth in Ethiopia. This report presentsfindings from an integrated multidisciplinary studythat was conducted to investigate the implicationsof this development. The study comprised threecomponents: i) an environmental flow evaluation; ii)a stakeholder analysis of the impact of currentinfrastructure and water management; and iii)computer modeling of future water resourcesdevelopment. The study found that existing waterresources development, for hydropowergeneration, has modified flows downstream of thelake, reduced water levels of the lake andsignificantly decreased flow over the Tis IssatWaterfall. Interviews with stakeholders indicate thatthe changes have benefited some people but have
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1
Evaluation of Current and Future Water ResourcesDevelopment in the Lake Tana Basin, Ethiopia
Matthew McCartney, Tadesse Alemayehu, Abeyu Shiferaw and Seleshi Bekele Awulachew
Introduction
Effective water resources development is widelyrecognized as crucial for sustainable economicgrowth and poverty reduction in developingcountries (World Bank 2004; Grey and Sadoff2006). However, such development incurs costs aswell as benefits. In the past, large hydraulicinfrastructure as well as water transfers, from onecatchment to another, has resulted in unforeseenenvironmental and social costs, which in someinstances outweigh the benefits (WCD 2000; Kingand McCartney 2007). Consequently, great care isneeded in the planning and management of waterresources development. In order to maximizebenefits and minimize costs, it is essential thatdecision-making incorporates different stakeholder
perspectives and is based on informedassessments of the trade-offs associated withallocation of water resources between competingneeds (McCartney and Awulachew 2006).Multidisciplinary research, comprising objectiveanalyses, is vital to understand complex systemsand how development will impact people andecosystems (Gichuki and McCornick 2008).
As part of its strategy for economicdevelopment, as well as contributing to attainingthe Millennium Development Goals, the Governmentof Ethiopia has identified the Lake Tana catchment,located in the headwaters of the Blue Nile (knownin Ethiopia as the Abay River) (Figure 1), as aregion with high priority for infrastructure
Hydropower stationsMajor townsMain rivers
Potential irrigation schemes
Watershed boundary
FIGURE 1. Map showing the Lake Tana and Beles River catchments and future irrigation and hydropower development.
2
investment. This includes the intention to transferwater to the adjacent Beles River catchment andis within the overall context of plans for significantwater resources development (i.e., primarily forhydropower and irrigation) throughout the whole ofthe Blue Nile Basin, both in Ethiopia and Sudan(Awulachew et al. 2008; Block et al. 2007;McCartney et al. 2009).
Lake Tana is important, directly and indirectly,for the livelihoods of many people, but currently thewater resources of the catchment are largelyunexploited. At present, there is a single dam atthe outlet of the lake called the Chara Chara Weir1.This regulates outflow from the lake for hydropowergeneration. The intention is, in future, to stimulateeconomic growth and reduce poverty through theconstruction of additional infrastructure, specificallyhydropower and irrigation schemes (MoFED 2006).To this end, the Tana and adjacent Belescatchments have been identified as one of five“growth corridors” in the country and an integratedwater resources development plan is beingimplemented (World Bank 2008).
This report comprises a synthesis of findingsfrom three component studies conducted to assess
the implications of water resources development inthe Lake Tana catchment. These were:
i) An environmental flow evaluation, conducted toestimate the environmental flow requirementsof the Abay River, downstream of the CharaChara Weir;
ii) A stakeholder analysis of the Chara CharaWeir conducted to assess the opinions,interests and concerns of various stakeholders,in relation to past water infrastructuredevelopment; and
iii) A modeling study conducted to assess thelikely impact of planned future water resourcesdevelopment on lake water levels and thepossible implications for local people and otherstakeholders.
The next section of this report, The StudyArea, describes the natural characteristics, currentsocioeconomic situation and planned waterresources development in the catchment. Thefollowing sections each describe the researchcomponents and the major findings of the study.Finally, there is a discussion of the implications ofthe findings of the study and conclusions.
1 Although called the Chara Chara “Weir”, by international definitions the structure at the outlet of Lake Tana constitutes a largedam since it stores more than 3 million cubic meters (Mm3) of water (ICOLD 2003).
The Study Area
Natural Characteristics
Lake Tana is the source of the Blue Nile River.Located at an altitude of 1,786 meters above sealevel (masl), the surface area of the lake is 3,156km2. The climate of the area is largely controlledby the movement of the intertropical convergencezone, which results in a single rainy seasonbetween June and September. Rainfall is highlycorrelated with elevation. The mean annual rainfallover the catchment is approximately 1,326millimeters (mm) (SMEC 2008). Average annual
evaporation over the lake surface is approximately1,675 mm (SMEC 2008).
The catchment area at the lake outlet is15,321 km2. Since 1996, flow from the lake hasbeen regulated by the Chara Chara Weir. The lakeis fed by more than 40 rivers and streams, but93% of the water comes from four major rivers:Gilgel Abay, Ribb, Gumara and Megech (Figure 1).Mean annual inflow is approximately 4,986 Mm3y-1
(i.e., 158 m3s-1) and the mean annual outflow isapproximately 3,753 Mm3y-1 (i.e., 119 m3s-1) (SMEC2008).
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Under natural conditions, prior to theconstruction of the Chara Chara Weir, dischargefrom the lake was closely linked to rainfall andthere was considerable seasonal and interannualvariability. Typically, the lake water level fluctuatedbetween 1,785.75 and 1,786.36 masl (Figure 2).Since the dam became fully operational in 2001(see section, The Current SocioeconomicSituation), the seasonal variation in flows hasgreatly reduced.
The plains surrounding the lake (i.e., theDembiya, Fogera and Kunzila plains in the north,east and southwest, respectively) form extensive(1,600 km2) wetlands during the rainy season. Asa result of the high heterogeneity in habitats, thelake and surrounding riparian areas support highbiodiversity and are listed in the top 250 lakeregions of global importance for biodiversity(www.worldlakes.org/lakedetails.asp?lakeid=8568).A quarter of the nearly 65 fish species found in thelake are endemic. The lake contains 18 species ofbarbus fish (i.e., of the Cyprinidae family) and theonly extended cyprinid species flock in Africa
(LakeNet 2004). In the area there are at least 217bird species and the lake is estimated to hold aminimum of 20,000 waterbirds (EWNHS 1996).
The Current Socioeconomic Situation
The total population in the lake basin was estimatedto be in excess of 3 million in 2007 (CSA 2003). Thelargest city on the lakeshore, Bahir Dar, has apopulation of over 200,000 and at least 15,000 peopleare believed to live on the 37 islands in the lake(www.worldlakes.org/lakedetails.asp?lakeid=8568).The majority of the population are dependent onrainfed agriculture. Cultivation practices are primitiveand crop production and livestock raising are closelyintegrated. Despite significant potential, there iscurrently very little irrigated agriculture in the basin.Recent data are hard to come by, but of theestimated 517,500 ha cultivated, traditional small-scale irrigation is practiced on only a small fraction(ca. 500 hectares (ha)). In some places, farmerspump water from the rivers flowing into Lake Tana,
FIGURE 2. Lake level and monthly outflow from Lake Tana (Source: SMEC 2008; MOWR hydrological database).
0
500
1,000
1,500
2,000
2,500
3,000
1,781
1,782
1,783
1,784
1,785
1,786
1,787
1,788
Jan
-60
Jan
-62
Jan
-64
Jan
-66
Jan
-68
Jan
-70
Jan
-72
Jan
-74
Jan
-76
Jan
-78
Jan
-80
Jan
-82
Jan
-84
Jan
-86
Jan
-88
Jan
-90
Jan
-92
Jan
-94
Jan
-96
Jan
-98
Jan
-00
Jan
-02
Jan
-04
Ou
tflo
w (M
m3 )
Wat
er le
vel (
mas
l)
Lake level Outflow
Before regulation After regulation
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but the current areal extent of this is unknown. Large-scale irrigation is planned but currently very little hasbeen constructed. Recession cropping, mainly formaize and rice (ca. 6,000 ha), is carried out in thewetlands adjacent to the lakeshore (World Bank2008).
The potential for wild fish production of LakeTana is estimated to be 13,000 tonnes per annum,but the current production is only about 1,000tonnes per year (Berhanu et al. 2001). Manypeople live on the islands and close to thelakeshore, at locations where there are no roads.Consequently, boat transport is vitally important. Formany centuries, the Negede or Weito people, alocal ethnic group, have built boats known as‘tanquas’ from the papyrus reeds (Gebre et al.2007). Tanquas are still widely used, but in recenttimes, some modern fishing boats have beenintroduced. Ferries also make regular servicesbetween the islands.
The Lake Tana region is endowed with manycultural and natural assets. Key amongst these
are approximately 20 monasteries, dating from thesixteenth and seventeenth century, located on thelake islands. Also, the Tis Issat Falls, one ofAfrica’s greatest waterfalls, is located on the BlueNile approximately 35 ki lometers (km)downstream from the Lake Tana outf low.Consequently, the area is an important touristdestination. It is estimated that close to 30,000people (both domestic and foreign) visit the areaeach year (EPLAUA 2006).
A hydropower plant was constructed by theEthiopian Electricity Light and Power Authority(EELPA) at Tis Abay in 1964. Located close to theTis Issat Falls (Figure 3), the station (Tis Abay-I)was initially used to provide electricity for a textilefactory and for domestic supply to the city of BahirDar. By diverting water from upstream of the Fallsthe power plant makes use of the natural 46 mhead of the Falls. The installed capacity of thepower plant is 11.4 megawatts (MW) and itoriginally relied entirely on the diversion of thenatural flow of the river.
FIGURE 3. Schematic of the Abay River (Blue Nile) downstream of Chara Chara Weir (not to scale).
Desilting channel Blue Nile Falls
Lake Tana
Abay River (Blue Nile)
Canal
Tis Abay-II
Tis Abay-I
Intake gates
Chara Chara Weir
Tributary inflow
Andassa River
Flow gauging station
Power station
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The concept of building a dam to regulate theoutflow from Lake Tana was first suggested in theearly years of the twentieth century. However,construction of the dam was not completed untilMay 1996. Initially, the dam had only two gates,each with a capacity of 70 m3s-1, and providedsufficient regulation only to improve the powerproduction from Tis Abay-I. An additional five gates,each also with a capacity of 70 m3s-1, were addedto the dam in 2001 and a second power station(Tis Abay-II), with an installed capacity of 72 MW,was built 100 m downstream of Tis Abay-I (Figure3). Since then the dam has been operated by theEthiopian Electric Power Corporation (EEPCO) (thesuccessor to the EELPA) to maximize electricityproduction from both power stations. Currently, thetwo stations represent 10% of the total grid-basedelectricity generating capacity of the country (814MW) (www.eepco.gov.et/eepco.htm). Combined, thetwo power stations generate approximately 440gigawatt hours (GWh) y-1.
The Chara Chara Weir regulates water storagein Lake Tana over a 3 m range of water levels from1,784 masl2 to 1,787 masl. The active storage ofthe lake between these levels is 9,100 Mm3, whichrepresents approximately 2.4 times the averageannual outflow. At full supply level, the total flowthrough the seven gates is 490m3s-1.Approximately 110 m3s-1 (i.e., the total flowcapacity of both stations Tis Abay-I and Tis Abay-II) can be released continuously with 95% reliability(Bellier et al. 1997).
Regulation for power production has modifiedthe natural lake-level regime, resulting in reducedseasonal but greater interannual variability (Figure2). The lowest level ever recorded (1,784.4 masl)was in June 2003. This was a drought year inmuch of Ethiopia and hydropower production wasconstrained in many places. In an attempt tomaintain electricity supplies, production at both TisAbay power stations was maximized and as aresult lake levels dropped sharply. As aconsequence of the low lake levels in 2003,navigation ceased for approximately four months(i.e., when lake levels dropped below 1,785 masl,the minimum level at which ships can currently
operate safely), large areas of papyrus reed weredestroyed, there was significant encroachment ofagriculture on the exposed lake bed and there wasa decrease in fisheries production (EPLAUA 2004).
Planned Water ResourcesDevelopment
As a result of its significant water resourcespotential, the Lake Tana catchment is at the coreof Ethiopia’s plans for economic development. Anumber of schemes are planned for the nearfuture. Currently, the Tana-Beles hydropower projectis under construction. This scheme involves thetransfer of water from the western side of LakeTana to the Beles River via a 12 km long, 7.1 mdiameter tunnel (Salini and Mid-day 2006). TheBeles River is a tributary of the Abay River, withheadwaters close to Lake Tana. However, theconfluence of the Beles and Abay rivers isapproximately 850 km downstream of Lake Tana(Figure 1). As a result, in contrast to the currentsituation where water diverted for the Tis Abaypower stations reenters the river just a short waydownstream, water diverted from Lake Tana to theBeles River will be effectively “lost” from the Abayfor almost the entire length of the river.Nevertheless, it will flow back into the river justbefore it crosses the border into Sudan.
The aim of the intra-basin transfer is togenerate hydropower by exploiting the 311 mdifference in elevation between the lake and theBeles River. A power station, generating a capacityof 460 MW, is being built in the Upper Belescatchment. This will enable far more electricity tobe generated than is currently produced by the TisAbay power stations. The intention is to divertapproximately 2,985 Mm3 through the tunnel (ratherthan via the Chara Chara Weir) each year togenerate 2,310 GWh of electricity (SMEC 2008).After passing through the power station, water willbe discharged to the Jehana River, a tributary ofthe Beles River. Both Tis Abay power stations willbe mothballed and only used in emergencies orwhen lake levels are very high.
2 During the construction of the weir, the riverbed at the lake outlet was lowered from 1,785 to 1,784 masl.
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TABLE 1. Planned irrigation development in the Lake Tana catchment (Source: BCEOM 1998; Mott MacDonald 2004;WWDSE and ICT 2008; WWDSE and TAHAL 2008a, 2008b).
Irrigation Irrigable Estimated Estimated Large dam Stage of developmentscheme area (ha) annual gross net water storage
water demand demand (Mm3)(Mm3)+ (Mm3)+
Gilgel Abay B 12,852 104 – 142 88 – 121 563 Feasibility studies ongoing
Gumara A 14,000 115 98 59.7 Feasibility studies completed
Ribb 19,925 172 – 220 146 – 187 233.7 Feasibility studies completed
Megech 7,300 63 – 98 54 – 83 181.9 Feasibility studies completed
Jema++ 7,800 57 48 173 Feasibility studies ongoing
Koga 6,000 62 52 78.5 Under construction
Northeast LakeTana 5,745 50 – 62 43 – 53 Withdrawals Pre-feasibility studies completed
from the lake
Northwest Lake 6,720 54 46 WithdrawalsTana from the lake Identification
Southwest Lake 5,132 42 36 WithdrawalsTana from the lake Identification
Notes: + Demands estimated through crop water modeling and presented in feasibility study reports. Where a range of demands is presented this reflects alternative cropping patterns. Gross – net demand is water returned to the rivers.
++ The scheme was not considered in the current study due to lack of reliable data.
In addition, a number of irrigation schemes(ultimately totaling approximately 70,000 ha) areplanned on the main rivers flowing into LakeTana (Table 1).
Of these schemes, only the Koga irrigation
Impacts of the Chara Chara Weir on Lake Tana Outflow andEnvironmental Flow Assessment
This component of the study comprised anevaluation of the impact of the Chara Chara Weiron outflow from Lake Tana and an estimate ofenvironmental flow requirements in the river reachcontaining the Tis Issat Falls. These werecompared with the actual flows in the river sincethe dam became fully operational in 2001.
Currently, Ethiopian law (through proclamationnumber 9/1995 passed in 2002) requires that, forall major development projects, an environmental
impact assessment (EIA) is conducted and thatenvironmental impacts should be minimized.However, there is no specific requirement forenvironmental flows to be maintained. Although theChara Chara Weir was constructed prior toproclamation 9/1995, an EIA was conducted. Aspart of this assessment, an attempt was made toestimate flow requirements over the Tis Issat Falls.However, the focus was on tourist needs and sothis evaluation was based primarily on the
project (6,000 ha) is current ly underconstruction. However, for several of the otherschemes detailed feasibility studies have beenundertaken and planning is at an advancedstage.
7
appearance of the Falls under different flow regimes(Bellier et al. 1997). The maximum flows wererecommended, not for the wet season when flowswould naturally be highest, but to make the Fallslook most dramatic during the peak tourist seasonfrom December to February (Table 2).
More recently, the EIA conducted for the TanaBeles transfer scheme recommended releasesfrom the lake with an annual average of 17 m3s-1
(i.e., 536 Mm3y-1) and an absolute minimum flow of10m3s-1 (Salini and Mid-day 2006). Although notbased on an ecological study, these flows, incombination with tributary inflows, were deemedadequate to maintain the ecology of both the upperriver and the Falls.
Method
In recent years, there has been a rapid proliferationof methods for estimating environmental flows,ranging from relatively simple, low-confidence,desktop approaches, to resource-intensive, high-confidence approaches (Tharme 2003). Thecomprehensive methods are based on detailedmultidisciplinary studies, which often involve expertdiscussions and the collection of large amounts ofgeomorphological and ecological data (e.g., Kingand Louw 1998). Typically, these studies takemany months, sometimes years, to complete.
A key constraint to the application ofcomprehensive methods, particularly in developingcountries, is the lack of data linking ecologicalconditions to specific flows. To compensate forthis, several methods of estimating environmentalflows have been developed that are based solelyon hydrological indices derived from historical data.Although it is recognized that a myriad of factorsinfluence the ecology of aquatic ecosystems (e.g.,temperature, water quality and turbidity), the
common supposition of these approaches is thatthe flow regime is the primary driving force (Richteret al. 1997).
One such method that can be applied is theDesktop Reserve Model (DRM). This is intended toquantify environmental flow requirements when arapid appraisal is needed and data availability islimited (Hughes and Hannart 2003). It should beviewed only as a preliminary step in derivingenvironmental flows. Ideally, flow estimatesgenerated by the model should be refined basedon far more extensive and detailed ecological andlivelihood studies that quantify the links betweenchanging river flows and natural resources, andhence the likely impacts for riparian people.
The DRM is built on the concepts of thebuilding block method, which was developed bySouth African scientists over several years (King etal. 2000), and is widely recognized as a scientificallylegitimate approach to setting environmental flowrequirements (Hughes and Hannart 2003). TheBuilding Block Method is developed on the premisethat, under natural conditions, different flows playdifferent roles in the ecological functioning of a river.Consequently, to ensure sustainability, it isnecessary to retain key elements of natural flowvariation. Hence, so called Building Blocks aredifferent components of flow which, when combined,comprise a regime that facilitates the maintenanceof the river in a pre-specified condition. The flow“blocks” comprise low discharges as well as highdischarges required for channel maintenance.Different estimates are derived for “normal years” and“drought years”. The flow requirements in normalyears are referred to as “maintenance requirements”.The flow requirements in drought years are referredto as “drought requirements” (Hughes 2001). TheDRM provides estimates of these building blocks forboth maintenance and drought requirements for eachmonth of the year.
TABLE 2. Recommended flow over the Tis Issat Falls from the Chara Chara Weir EIA.
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total
Flow (m3s-1) 60 60 10 10 10 10 20 20 40 40 40 60
Volume (Mm3) 161 146 27 26 27 26 54 54 104 107 104 161 997
(Source: Bellier et al. 1997)
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The DRM has been used extensively in SouthAfrica. Its use in other African countries is limited,but it has been applied in Swaziland, Zimbabwe,Mozambique (Hughes and Hannart 2003) andTanzania (Kashaigili et al. 2007). The model andsimilar hydrological approaches have also beenused in India and elsewhere in Asia (Jha et al.2008; Smakhtin et al. 2006). The model comprisesempirically derived statistical relationshipsdeveloped through an analysis of comprehensiveenvironmental flow studies. This found that riverswith more stable flow regimes have relatively higherflow requirements than rivers with more variableflow regimes. This is because in highly variable flowregimes the biota will have adjusted to the relativescarcity of water, whilst in more reliably flowingrivers the biota are more sensitive to reductions inflow (Hughes and Hannart 2003).
Change in Hydrological RegimeCaused by the Chara Chara Weir
A gauging station, located immediately downstreamof the outlet from Lake Tana (catchment area15,321 km2), has operated continuously since1959. The intermediate catchment between theChara Chara Weir and the diversion to the TisAbay power stations has an area of 1,094 km2. Theprincipal tributary between the lake and Tis Abayis the Andassa River, which is gauged justupstream of its confluence with the Blue Nile(Figure 3). The catchment area at the AndassaRiver gauging station (which has also operatedsince 1959) is 573 km2.
Time series of monthly flow data from January1959 to December 2006 were obtained for bothgauging stations from the Ministry of WaterResources. Daily flow series from January 1973 toDecember 2006 were obtained for both stations. Anestimate of the contribution from the ungaugedportion of catchment downstream of the lake outletwas derived simply by multiplying the flow seriesderived from the Andassa gauge using an area-weighting. The flows downstream of Lake Tana wereadded to the flows from the outlet to provide anestimate of the total flow at the diversion to thepower stations. Turbine discharge data for both TisAbay-I and Tis Abay-II power stations were obtainedfrom EEPCO and used to estimate the monthlyflows diverted to produce electricity as well as thewater remaining in the river to flow over the Falls.
Analyses of flows were conducted over threetime periods: May 1959 to April 1996, May 1996 toDecember 2000, and January 2001 to December2006. These periods correspond to different levelsof regulation of the Lake Tana outflow (Table 3).
Figure 4 shows the mean monthly flow,measured immediately downstream of the CharaChara Weir for the three periods investigated. Theresults from May 1959 to April 1996 indicate theextreme seasonal variability in the natural flowregime, ranging from a mean of 346 m3s-1 inSeptember to just 12 m3s-1 in June. On average,only 12% of the natural discharge from the lakeoccurred in the five months from February to June.In the period May 1996 to December 2000, bothwet and dry season flows were significantly higherthan those which occurred during the previousperiod. The higher dry season flows were a
TABLE 3. Periods of different flow regulation from Lake Tana.
Period Description
May 1959 - April 1996 No regulation of outflow from Lake Tana. Diversions to the Tis Abay-I power station,directly from the Abay River, commenced in January 1964.
May 1996 – December 2000 Two-gate Chara Chara Weir becomes operational in May 1996. Operated to regulateflow to the Tis-Abay-I power station.
January 2001 – December 2006 Five new gates constructed and become operational in January 2001. Operated toregulate flow to both the Tis Abay-I and Tis Abay-II power stations.
9
consequence of partial flow regulation by the two-gate Chara Chara Weir. The higher wet seasonflows were a consequence of above average rainfallduring these years, particularly in 1998. Meanannual flow in 1998 (196.0 m3s-1; 6,182 Mm3) wasthe highest annual discharge measured in thewhole 48-year record. The results for the periodfrom January 2001 to December 2006 illustrate themuch higher dry season flows and reduced wetseason flows arising as a consequence of the fullflow regulation by the Chara Chara Weir. As aconsequence of regulation, there is much lessseasonal variability in flow from the lake. After 2001,43% of the discharge from the lake occurred in thefive months from February to June.
The data provided by the EEPCO indicate thatwhen only the Tis Abay-I power station wasoperational (i.e., from 1964-2000) average annualturbine discharge was just 192 Mm3 (i.e., 6.1 m3s-1).Throughout this period just 4.5% of the average
annual discharge at Tis Abay (4,227 Mm3) wasdiverted. Since 2001, when the Tis Abay-II powerstation came into operation, the average annualturbine discharge has increased to 3,090 Mm3
(i.e., 97.9 m3s-1). This equates to 72% of theaverage annual discharge at Tis Abay (4,306 Mm3)between 2001 and 2006.
Diversions to the original Tis Abay-I powerstation had very little impact on the flows over theTis Issat Waterfall. Between 1964 and 2000 averageannual discharge over the Falls is estimated to havebeen 128 m3s-1 (i.e., 4,040 Mm3). By comparison,between 2001 and 2006 the average annualdischarge over the Falls is estimated to have beenjust 41 m3s-1 (i.e., 1,305 Mm3), with a minimum ofjust 4.7 m3s-1 (i.e., 147 Mm3) in 2004 and less than12 m3s-1 (i.e., 378 Mm3) in both 2003 and 2005.Between 2001 and 2006, in many months, themean discharge was less than 50% of what it wasprior to 2001 (Figure 5).
FIGURE 4. Mean monthly flow (m3s-1) from Lake Tana for three periods of different flow regulation.
0
100
200
300
400
500
Jan
Feb
Mar
Ap
r
May Jun
Jul
Au
g
Sep
Oct
No
v
Dec
Mea
n m
on
thly
flo
w (m
3 S-1)
May 1959-Apr 1996 May 1996-Dec 2000 Jan 2001-Dec 2006
May-1959 May-1996 Jan-2001
Apr-1996 Dec-2000 Dec-2006
Jan 77.4 127.4 97.6
Feb 53.2 84.0 98.7
Mar 33.4 57.3 109.3
Apr 20.2 69.1 109.9
May 12.9 41.4 94.3
Jun 11.5 39.1 95.0
Jul 34.8 75.5 116.5
Aug 168.8 184.6 127.8
Sep 345.9 449.0 204.4
Oct 309.7 423.8 150.8
Nov 200.7 297.4 122.6
Dec 125.6 177.7 109.3
Average 116.2 168.9 119.7
10
Estimated Environmental FlowRequirements
The DRM was used to estimate environmental flowrequirements in the river reach between the diversionto the Tis Abay power stations and the point wherethe water currently returns to the river. This reachincludes the Tis Issat Falls. To estimateenvironmental flow requirements, the model needs anaturalized flow series as input. Prior to theconstruction of the two-gate Chara Chara Weir,outflows from Lake Tana were unmodified and sorepresent a naturalized flow series. These data wereused as input to the model. For the flow over theFalls, the contribution of flow from the Andassa Riverand the rest of the catchment between Lake Tanaand the Falls was added to the Lake Tana outflowseries. Some data were missing. Single months ofmissing data during periods of declining flow werefilled by interpolation. However, in cases where therewere consecutive months of missing data or wheremissing data occurred during periods when flowswere rising, this was not possible and as a resultthe entire year was eliminated from the analyses. Atotal of four months were filled by interpolation andsix years were eliminated. Hence, a total of 31years of data were used as input to the model.
In South Africa, rivers are classified in relation toa desired ecological condition, and flow requirementsset accordingly. Six management classes aredefined, ranging from A to F. Class A rivers are largelyunmodified and natural, and class F rivers areextremely modified and highly degraded (DWAF1999). Classes E and F are deemed ecologicallyunsustainable, so class D (i.e., largely modified) isthe lowest allowed “target” for the future status of ariver. This classification system is used in conjunctionwith the building block method and flow requirementsare computed accordingly; the higher the class, themore water is allocated for ecosystem maintenanceand the greater the range of flow variability preserved.In the current study, to reflect the importance ofwater abstractions for hydropower production, thedesired ecological condition of the Blue Nile was setas class C/D (i.e., moderately to largely modified).This means that the flow regime will change in sucha way that there is likely to be loss and change ofnatural habitat and biota (possibly including fish) butthe basic ecosystem functions of the system will onlybe moderately altered (Kleynhans 1996). No explicitallowance was made for the aesthetic quality of theflows. However, because the method incorporates theecological value of higher flows, larger environmentalflow requirements are estimated for the months in
FIGURE 5. Comparison of flow over the Tis Issat Falls for the periods 1964-2000 and 2001-2006.
0
50
100
150
200
250
300
350
400
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Mea
n m
on
thly
flo
w (m
3 s-1)
1964-2000 2001-2006
11
which they would occur naturally (i.e., August toDecember). This is in contrast with the original EIAconducted for the Chara Chara Weir, where tourist“needs” were given primary consideration and thehighest flows were recommended at peak touristtimes (i.e., December to February) (Bellier et al.1997). For the more recent Tana-Beles EIA there areno recommendations on the timing of high flows(Salini and Mid-day 2006).
Figure 6 presents a comparison of theobserved time series and the environmental flow
series derived from the DRM for the river reachincluding the Falls. Results from the model indicatethat to maintain the river at class C/D requires anaverage annual environmental flow allocation of 862Mm3 (i.e., equivalent to 22% of the natural meanannual flow) (Table 4). This is the average annual“maintenance flow” calculated from the sum of boththe maintenance low flows (i.e., 626 Mm3) andmaintenance high flows (i.e., 236 Mm3). Thedrought flows correspond to 11% of the meanannual flow (i.e., 440 Mm3).
FIGURE 6. Time series of monthly observed flow and estimated environmental flows (1960-1995) for the reach of AbayRiver that includes the Tis Issat Falls (log scale on the y-axis).
10
100
1,000
10,000
Jun
-60
Jun
-62
Jun
-64
Jun
-66
Jun
-68
Jun
-70
Jun
-72
Jun
-74
Jun
-76
Jun
-78
Jun
-80
Jun
-82
Jun
-84
Jun
-86
Jun
-88
Jun
-90
Jun
-92
Jun
-94
Mo
nth
ly fl
ow
vo
lum
e (M
m3 )
Observed Flow (1960-1995) DRM Estimated Environmental Flows
12
TABLE 4. Summary output from the Desktop Reserve Model applied to the reach of the Tis Issat Falls based on1960-1995 monthly flow series.
Annual Flows (Mm3 or index values)
MAR = 4,017 Total Environmental flow = 862 (22% MAR)
SD = 1,293 Maintenance Low flow = 626 (16% MAR)
CV = 0.322 Drought Low flow = 440 (11% MAR)
BFI = 0.37 Maintenance High flow = 236 (6% MAR)
Observed flow (Mm3) Environmental flow requirement (Mm3)
Maintenance flows Drought flows
Month Mean CV Low High Total
Jan 217 0.35 68 0 68 48
Feb 135 0.34 56 0 56 39
Mar 97 0.31 42 0 42 30
Apr 58 0.29 28 0 28 20
May 42 0.35 22 0 22 16
Jun 44 0.46 20 1 21 10
Jul 180 0.43 27 11 38 20
Aug 590 0.38 51 33 84 36
Sep 946 0.39 77 115 192 54
Oct 839 0.36 84 33 117 59
Nov 526 0.33 78 31 109 55
Dec 345 0.33 74 12 86 52
Note: MAR – Mean Annual Runoff; SD – Standard deviation; CV – coefficient of variation; BFI – Baseflow Index
For the period 2001 to 2006, average annualflows over the Falls (i.e., 1,306 Mm3) exceeded thetotal annual maintenance flow requirementspredicted by the model (i.e., 862 Mm3). However, amore detailed analysis shows that in most monthsaverage flows were significantly less than theenvironmental flow requirements predicted by themodel. For several months average flows were lessthan 70% of the estimated requirement (Table 5).Only in months July to October (i.e., wet seasonmonths) did the average flow over the period 2001to 2006 exceed the recommendation of the DRM(Table 5; Figure 7). This suggests that, in recent
years, dry season flows have been insufficient tomaintain even basic ecological functioning of thisreach of the Abay River. Furthermore, even thoughthe average over the period exceeds the DRMrecommendation, in several years even the wetseason flow was a lot less than recommended. Forexample, in September and October 2005, flowsover the Falls were estimated to have been just 44Mm3 and 7.6 Mm3 respectively; less than even therecommended minimum drought flows. As well asecological implications these very low wet seasonflows significantly impair the visual spectacle of theFalls (Figure 8).
13
TABLE 5. Comparison of environmental flow requirements computed by the DRM and observed mean monthly flows in theriver reach that includes the Tis Issat Falls, between 2001 and 2006.
Month Total Observed Ratio of observed tomaintenance flows environmental flow requirementrequirements
Mm3/month Mm3/month
Jan 68 44 0.64
Feb 56 36 0.64
Mar 42 36 0.85
Apr 28 22 0.81
May 22 21 0.96
Jun 21 16 0.76
Jul 39 178 4.57
Aug 83 252 3.03
Sep 192 352 1.83
Oct 117 196 1.68
Nov 109 92 0.85
Dec 86 61 0.71
Annual 863 1,306
FIGURE 7. Comparison of mean monthly environmental flow requirement estimated using the DRM, with the recommendationof the Chara Chara EIA and the actual flows over the Tis Issat Falls.
0
100
200
300
400
Jan
Feb
Mar
Ap
r
May
Jun
Jul
Aug Se
p
Oct
No
v
Dec
Flo
w (M
m3 )
Environmental flow estimate from DRM Flow recommended by Chara Chara EIA
Actual flow (2001-2006)
14
Operation of the Chara Chara Weir has alteredthe flow regime of the Abay River. Between theoutlet from Lake Tana and Tis Abay, the regulationhas significantly increased dry season, andsignificantly decreased wet season, flows. Noecological surveys have been conducted, but studieselsewhere in the world have shown that reducedinter-seasonal variability has an impact on theecology of the river, benefiting those species thatdepend on more regular flows whilst adverselyimpacting those species adapted to seasonal drying(Ward and Stanford 1995). It can also be speculatedthat the changes in flow are likely to have affectedsediment transport and altered water chemistry andtemperature regimes. Although the consequences ofthese changes may not be apparent for manydecades, it is possible that, again as has beenfound elsewhere, they will modify channel
morphology and substrate composition, as well asriver biota (Bergkamp et al. 2000).
Since 2001, flows in the reach containing theFalls have been significantly reduced as aconsequence of diversions to the power stations.Again, although no ecological surveys have beenconducted, there is little doubt that the reductionin flows will have had very severe consequences formany species including aquatic macrophytes,benthic organisms and fish (Staissny 1996). Thereduced flows are also very likely to have hadadverse impacts on many riparian species. Bychanging the magnitude and extent of inundation,and altering land-water interaction, the change inflows may have disrupted plant reproduction. Overtime it may allow the encroachment of uplandplants previously prevented by more frequentflooding (Nilsson et al. 1997).
FIGURE 8. Photographs to illustrate how the wet season visual spectacle of the Tis Issat Falls have been altered as aconsequence of upstream diversions to the Tis Abay hydropower station.
15
Stakeholder Analysis of the Chara Chara Weir
The stakeholder analysis of the Chara Chara Weir,conducted between May and July 2007, wasundertaken to assess: i) the opinions, interests,and concerns of various stakeholders, in relation tothe dam’s socioeconomic and environmentalimpacts; and ii) procedures for decision-making inrelation to dam operation. The stakeholders aredifferent community and livelihood groups, as wellas a range of relevant government and privateorganizations. Multiple data gathering instruments,essentially of a qualitative nature (i.e., in-depth(partly structured) interviews with relevantspecialists and community leaders, and focusgroup discussions), were employed to generateinformation about stakeholder perceptions of thedam, its management and its impact on naturalresources and livelihoods. The data gathering wasundertaken by a professor and his assistant fromthe Department of Sociology and SocialAnthropology at Addis Ababa University.
Identified stakeholders were divided intoprimary, secondary and tertiary groups:
1) The primary stakeholders are those who aredirectly affected on a daily basis by operationof the dam. They encompass: i) farmers livingupstream of the dam, in close proximity to theshore of the lake, as well as those living closeto the river downstream of the dam, between itand the Tis Abay power stations; ii) fishers,comprising both artisanal fishers utilizing reedboats as well as commercial fishers utilizingmotorized boats; iii) papyrus boat builders –the Negede; iv) the EEPCO which isresponsible for day-to-day operation of thedam; and v) private enterprises with a vestedinterest in tourism, including hotels and theoperators of tour boats.
2) The secondary stakeholders are those whodirectly represent the interests of the primarystakeholders. They include: i) the Lake TanaTransport Enterprise (TTE), responsible foroperating the ferries and overseeing navigationon the lake; and ii) the Fishers Cooperativewho represent fishers on the lake and promotefisheries development.
3) The tertiary stakeholders are regionalgovernment departments that make policiesand decisions that affect the lake and thelivelihoods of people living in its vicinity. Localresearch institutes, conducting research in thearea were also included in this category. Theyinclude: i) the Amhara Region Bureau of WaterResources (ARBWR); ii) the Amhara RegionEnvironmental Protection, Land Administrationand Use Authority (EPLAUA); iii) the AmharaParks Development and Protection Authority(PaDPA); iv) the Amhara Region Bureau ofCulture and Tourism (ARBCT); v) the LakeTana Basin Research Centre (LTBRC); and vi)the Amhara Region Agricultural ResearchInstitute (ARARI).
Identified Issues and Concerns
The study identified a range of issues andcompeting interests between the primarystakeholders, which are leading to conflicts insome instances (Table 6). There is no doubt thatthrough the production of electricity, the CharaChara Weir and Tis-Abay power stations havecontributed significantly to the economy of Ethiopia.However, whilst some local people have gained asa result of the dam, others have lost.
16
TABLE 6. Summary of issues identified by different stakeholders.
Stakeholders Issues Identified
Primary
EEPCO NC NC NC NC NC -ve NC NC + ve
Upstream farmers + ve - ve NC NC NC NC - ve NC NC
Downstream farmers NC NC + ve + ve -ve - ve NC NC - ve
Fishers - ve NC NC NC NC NC - ve - ve NC
Negede - ve NC NC NC NC NC - ve - ve NC
Hotel owners - ve - ve NC NC NC - ve NC - ve + ve
Tour boat operators - ve NC NC NC NC NC NC NC NC
Secondary
Tana Transport Enterprise - ve NC NC NC NC NC NC NC NC
Fishers Cooperative - ve NC NC NC NC NC - ve - ve NC
Tertiary
Amhara Culture and Tourism Bureau - ve - ve NC NC NC NC NC NC + ve
Amhara Region Bureau of WaterResources NC - ve NC NC NC NC NC NC + ve
Amhara Region EnvironmentalProtection, Land Administration andUse Authority - ve NC NC NC NC - ve - ve - ve NC
Amhara Parks Development andProtection Authority - ve NC NC NC NC NC - ve - ve NC
Lake Tana Basin Research Centre - ve NC NC NC NC - ve - ve - ve NC
Amhara Region Agriculture ResearchInstitute - ve NC NC NC NC - ve - ve - ve NC
Notes: +ve = positive impact; -ve = negative impact; NC = not an expressed concern
Red
uced
lak
e le
vels
in t
he d
ry s
easo
n
Wet
sea
son
flood
ing
Incr
ease
d dr
y se
ason
flow
s in
Upp
er A
bay
Red
uced
dow
nstr
eam
flood
ing
Lack
of
war
ning
of
high
flo
ws
dow
nstr
eam
Red
uced
flo
w o
ver
the
Tis
Iss
at F
alls
Loss
of
vege
tatio
nar
ound
the
lake
Dec
linin
g la
ke f
ish
popu
latio
n
Ele
ctric
ity p
rodu
ced
The EEPCO noted the importance of the TisAbay power plants for electricity generation inEthiopia and see the power production as both aregional and national benefit. The companyspokesman highlighted the Universal ElectrificationAccess Programme which aims to increaseaccess to electricity from 15 to 50% of thepopulation over the five years from 2005 to 2010.Between 2005 and 2007, the EEPCO claims tohave increased access to 22% with an additional758 towns and villages electrified in 2007. Thecompany recognizes that the diversion to thepower stations is adversely affecting the visual
spectacle of the Tis Issat Falls. However, thespokesman emphasized the fact that the shift toelectricity lessens environmental degradation byreducing biomass fuel requirements. The company,therefore, believes that the power stations haveoverall resulted in a net environmental benefit. Itwas acknowledged that the cost of electricalappliances, in particular stoves and cookers, limitsuptake by poor rural households.
Farmers living both upstream and downstreamof the dam have broadly benefited from it. Inupstream locations, increased drawdown of the lakehas resulted in increased exposure of the lake bed
17
and encouraged the practice of dry seasonrecession agriculture. In 2003, the lake was drawndown to its lowest recorded level, farmersextended crop production onto about 562 ha of thelake bed, utilizing the moist nutrient-rich siltdeposits for both horticultural and cereal crops(EPLAUA 2004). Downstream of the dam, farmershave benefited from reduced wet season floodingand, because of the guaranteed flows andconsequent access to water in the dry season,have expanded small-scale irrigation schemes.Women, who collect water from the river for drinkingand household use, have benefitted as aconsequence of easier access in the dry season.One farmer downstream of the dam stated:
The weir has not caused us harm in anyway. In fact, we are getting a greatersupply of water in the dry seasonbecause of it.
Other people have been adversely affected bythe dam. Many of those living in the smallcommunity of Tis Abay, adjacent to the powerstations and very close to the Tis Issat waterfallcomplained that they have been negativelyimpacted. Surprisingly, the number of touristsvisiting the Falls has increased in recent years(Shiferaw 2007). This is partly the result of greaternumbers of tourists generally in Ethiopia and partlybecause the Falls are still promoted as a majortourist attraction. Many of the tourists who visitBahir Dar are unaware that flows over the Fallshave decreased. However, according to localpeople, many visitors are now unhappy with thevisual spectacle3 and, because they are annoyed,refuse to buy locally-made handicrafts. In the past,the selling of these products contributedsignificantly to the income of many local people.Although a few people have gained employment atthe power stations many have not. The loss ofincome from tourists has had a negative impact onthe livelihoods of many local people which have notbeen compensated through alternativeopportunities. The local community also complains
that they have no access to electricity, despite thefact that the power stations are located very closeto their vil lage. Furthermore, developmentopportunities (e.g., a school and health center)promised when the Tis Abay-II power station wasbuilt, have not been forthcoming. One local elderstated:
We have not benefited in any way fromthe power plant. This is despiteconstant appeals to the concernedregional authorities, filing petitions anumber of times and pursuing the caseover a long period [of time]. Fourhundred households were promisedelectric power supply by [the] EEPCOand [were] required to pay registrationfees for that purpose. However, it hasnot so far materialized and the area stillremains without access to electricity.
A significant number of people are dependenton fishing from Lake Tana for their livelihoods. Thedevelopment of the commercial fishery, usingmotorized boats, was initiated by an EU-sponsoredLake Fisheries Development Program in 1986. Theestablishment of the Fishers Cooperative inDecember 1994 has added impetus to thedevelopment of the sector. The current membershipof this cooperative is 150 fishers, of whom 134 aremen and 16 women. Fishers complain that sincethe dam was constructed, dry season drawdown ofthe lake has increased and resulted in desiccationof reed beds and consequent loss of fish breedinghabitat. This has been exacerbated by farmersclearing reeds to create fields. Extreme drawdownof the lake in 2003 made navigation difficult andresulted in the sinking of some boats when theyhit submerged rocks. One fisher stated:
The shrinking of the lake dried out plantspecies vital for the reproduction of fishstocks, resulting in [a] large loss ofmany fish varieties. That was not theonly dire consequence. The further thelake retreated, the larger the area of
3 This perception was validated by hotel managers who confirmed that tourists complained to them that the Falls are no longer asdescribed in tourist books, brochures and publicity material.
18
lakeshore that turned into dry groundwhere fishers could no longer cast theirnets. The fish have also moved furtherin toward the deeper parts of the lakewhich makes catching them moredifficult.
The Negede people have been particularly hardhit. They rely on papyrus reeds for much of theirlivelihood; using it to construct canoes for laketraders and other people who move around the lakeby boat. They also use the reeds to makehousehold utensils (such as baskets and mats)which they sell in local markets, both for utilitarianpurposes and as tourist souvenirs. In addition, theycut and sell papyrus trunks to urban people forfence making. Since the construction of the dam,they complain that many of the papyrus beds havedried out and large areas have died. As with thefishers, they also complain that farmers have burntand cleared reeds to cultivate crops. A Negedespokesperson stated:
We are extremely worried in relation tothe Chara Chara Weir. If Lake Tanacontinues to shrink as the weir drainsits water the likely scenario is that ourlivelihood will be destroyed, and togetherwith it our future. Conflict with farminggroups who cultivate the wetlands isunavoidable….
Many people living in the vicinity of the lake useboat transport on an almost daily basis to attendschool, visit health facilities and travel to and frommarkets. For example, many of the 10,000inhabitants of Dek Island (the largest lake island) aredependent on growing mangoes and on boats to getthese to markets. Tourists also use boats to travelto many of the islands to visit the monasteries. Thehead of the TTE stated that navigation on the lakeis seriously compromised when water levels dropbelow 1,785 masl. When this happened in 2003,the cost arising because of service interruption anddamage to boats is estimated to have been about4 million Ethiopian Birr (i.e., approximatelyUS$400,000) (Alemayehu 2008).
The government departments had differingviews on the dam and its operation. The ARBWRtook the view that the socioeconomic benefits
arising from the electricity produced significantlyoutweighed any costs. In contrast, staff at theEPLAUA expressed concerns over theenvironmental impacts of the dam and its operationand the associated impacts on the Negede, fishersand communities dependent on tourism. Staff at thePaDPA argued that the historic and cultural valueof the lake, as well as the river corridor to the TisIssat Falls, meant that the region should bedesignated as a protected area with much greaterrecognition of its heritage value in currentmanagement and future development planning.
Decision-Making Process
A common view, expressed by many stakeholdersand implicitly recognized by the EEPCO andgovernment departments, was that the decision-making processes in relation to both the planningand operation of the dam were not ideal. There islittle doubt that the general lack of stakeholderconsultation has fuelled controversies and resultedin widespread rumors and speculation about thefunction of the dam and its resultant impacts. Boththe TTE and the Fishers Cooperative complainedthat the interests of the stakeholders they representwere totally ignored in the planning of the dam.This has been exacerbated by the lack oftransparency and participation in decision makingrelated to the way the dam is now operated. Bothorganizations feel that the EEPCO’s soleconsideration is electricity generation and otherstakeholder needs are simply ignored. The directorof the LTBRC complained that they experiencedifficulties in obtaining data and information whichhelp to make informed assessments of the benefitsand costs of the dam and its operation.
A similar lack of transparency has been afeature of decision-making in other developmentprojects in Ethiopia. A study of the follow-up of theEIA conducted for the Koga irrigation scheme foundthat almost nonexistent public participation indecision-making was a major constraint toimplementation of EIA recommendations (Abebe etal. 2008). Similarly, with the Tana-Beles scheme,there has been little public consultation. Even
19
though it will most likely be commissioned thisyear, there is no general understanding of how itwill be operated. Although, it was not a primaryfocus of the research conducted, this study foundthat many stakeholders hope that, overall, thescheme will be beneficial for both the lake andthemselves. However, there is little understandingof the likely impacts of the scheme. Many
stakeholders simply believe that with the closingof the Tis Abay power stations, all the problemswill be resolved and the lake and downstream flowswill revert to a natural cycle. The fact that thewater transfer to the Beles River, in conjunctionwith the planned irrigation schemes, is likely toincrease pressure on the lake and require verycareful management is not widely appreciated.
Simulation of Future Water Resources Development
In this component of the study, the WaterEvaluation And Planning (WEAP) model was usedto investigate scenarios of future water resourcesdevelopment in the Lake Tana catchment. Themodel was used to investigate both the reliabilityof water availability for the planned schemes andtheir impact on lake water levels and lake surfacearea. The implications of water-level fluctuations onlake navigation were assessed. The implications ofmaintaining environmental flows downstream of thelake to the Tis Issat Falls were also ascertained.
Configuration of the WEAP Model tothe Lake Tana Catchment
The WEAP model was developed by the StockholmEnvironment Institute (SEI) in Boston and providesan integrated approach to simulating watersystems associated with development (Yates et al.2005). The WEAP model represents the system interms of its various supply sources (e.g., rivers,inter-basin transfers and reservoirs); withdrawals,transmission and wastewater treatment facilities;ecosystem requirements, and water demands (i.e.,typically comprising hydropower, irrigation,domestic supply, etc.). The model essentially
performs a mass balance of flow sequentially downa river system, making allowance for abstractionsand inflows. The model optimizes water use in thecatchment using an iterative Linear Programmingalgorithm, the objective of which is to maximize thewater delivered to demand sites, according to aset of user-defined priorities (SEI 2007).
The modeling of the Lake Tana catchmentencompassed the major tributaries to the lake,upstream of the proposed dams (i.e., water thatcurrently flows directly into the lake that will in futurebe affected by regulation from the dams), estimatesof flows downstream of the proposed dams and totalinflows on other rivers (i.e., flows that will beunaffected by future development) and Lake Tana(Figure 9). Lake Tana was simulated as a reservoir.The Andassa River was also included. The modelwas configured to run on a monthly time step.
As primary input to the WEAP model, theinflow series at the planned dam sites wereobtained from the relevant feasibility studies for theperiod 1960-2004. Where necessary inflow datawere augmented using area-weighted estimatesfrom the nearest available flow gauging station. Tosimulate the current situation, the Tis Abayhydropower plants were included as a demandnode on the Abay River, downstream of the lake.
20
The model was calibrated by trial and error.Calibration was undertaken by comparing thesimulated and observed lake water levels and theflow from the lake. The final selection of modelparameters was based on both quantitativeobjective functions (e.g., the Nash coefficient), andqualitative assessment of the goodness of fit,based on simple comparison of observed andsimulated water-levels and flows over the period1960-2004. The parameters modified were thosethat altered the natural flow from the lake andoperation of the Chara Chara Weir after 1995. Withthe selected parameters, for the flow thepercentage error in the mean annual value was9.0% and the Nash coefficient was 0.57. For thelake water level, error in the mean annual valuewas <1% and the Nash coefficient was 0.74.These values indicate that the model performancewas reasonable.
Description of Development Scenarios
Data for the various scenarios used in this studywere obtained from the Abay River Basin IntegratedDevelopment Mater Plan and the feasibility studiesconducted for each of the proposed schemes
(BCEOM 1998; Mott MacDonald 2004; WWDSEand ICT 2008; WWDSE and TAHAL 2008a, 2008b).These indicate how the water demand for bothirrigation and hydropower is likely to change in thecatchment in the future.
Four scenarios were developed based on thecurrent stage of scheme development and hence thelikelihood of full implementation (Table 7). Eachdevelopment scenario was run for the 36 years (i.e.,1960-1995). This period was selected, both becausedata are available and because it represents a widerange of hydrological variability. Furthermore, itrepresents years before construction of the CharaChara Weir and so the impact of each developmentscenario could be compared with the natural water-level regime of the lake.
In all cases, irrigation demand was computedbased on assumptions about cropping patterns(i.e., encompassing crop type and percentage ofcommand are util ized) and crop waterrequirements. In the feasibility studies, the FAOCROPWAT program (Allen at al. 1998) was usedto determine total irrigation requirement. In somecases, alternative cropping patterns weresimulated, but for the results presented here, thepattern that created the highest demand wasselected for all schemes. In all cases, allowances
FIGURE 9. Schematic of existing and planned water demand in the Lake Tana catchment as simulated in the WEAP model,showing the mean annual flow upstream of the proposed irrigation dams as well as unregulated flows into the lake.
Lake Tana
Regulated flows Unregulated flows (downstream of proposed dams and unregulated rivers)
Lake pumping schemes
246
1925
Abay (Blue Nile)
Tis Issat FallsTis Abay power plants
116Koga
Gilgel AbayMegech
Gondar town
Ribb Gumara
Intermediate flow
Beles hydropowertransfer
LegendIrrigation Scheme
116 Mean annual inflow (Mm3)
270Andassa
Dam
Withdrawals
Return flow
176 216 244
Rivers
2180
21
were made for transmission losses from canals.Return flows were estimated as 15% of the waterdiverted.
For the proposed new dams no operating rulecurves are currently available. Consequently, nooperating rules were incorporated within the WEAPmodel. This meant that the reservoirs were notdrawn down to attenuate wet season floods and norestrictions were applied on abstractions as thereservoirs emptied. The one exception was LakeTana, where the operating rule was derived fromthe pattern of operation in recent years. Thus,restrictions on drawdown were applied to reduceabstractions as lake levels dropped below 1,786masl and to ensure levels did not drop lower thanthe minimum operating level of 1,784 masl. Netevaporation (i.e., evaporation minus rainfall) wascomputed from rainfall and evaporation dataobtained from the meteorological station locatedclosest to each reservoir.
Since it provides the highest economic returns,electricity generation was designated a higherpriority than irrigation. The water demand fordomestic, municipal and industrial uses were notconsidered. This is because their impact on waterresources of the lake, both now and in the nearfuture, is insignificant (SMEC 2008).
TABLE 7. Summary of development scenarios (Source: BCEOM 1998; EEPCO database; and SMEC 2008).
Scenario Hydropower developed Irrigation schemes developed Total mean annual waterdemand (Mm3)+
Baseline Tis Abay I and II - 3,469Scenario (BS)
Ongoing Development Tana Beles transfer Koga 3,047Scenario (ODS)
Likely Development Tana Beles transfer Koga, Megech, Ribb, Gumara and 3,621Scenario (LDS) Gilgel Abay
Full Development Tana Beles transfer Koga, Megech, Ribb, Gumara, Gilgel 3,768Scenario (FDS) Abay and 3 schemes pumping directly
from the lake
Note: +water demand has been calculated using the highest crop water estimates for each of the irrigation schemes.
Each scenario was run with the flowrequirement for the Tis Issat Falls as recommendedin the most recent EIA conducted for the Tana-Beles transfer scheme. These flows were termedthe Tana Beles Flow (TBF) requirements4. Thescenarios were then repeated with the time seriesof environmental flow requirements estimated in thecurrent study using the DRM (see section,Estimated Environmental Flow Requirements).These flows were termed the VariableEnvironmental Flow (VEF) requirements. In bothcases, the proposed minimum instream flowsdownstream of each of the proposed irrigation dams(as identified in the feasibility studies and in allcases simply a minimum baseflow) were alsoincluded. In all cases, environmental flows weregiven higher priority than hydropower production.
Analyses of Output from the WEAPModel
For each scenario, the WEAP model was used topredict: i) the impacts on lake water levels and lakearea for each month of the 36 years simulated; andii) unmet demand for hydropower and irrigation inany month. In each scenario, the time series of
4 For the baseline scenario, flows released from the lake to provide water for the power station exceed the TBF environmental flowrequirements. However, most of the water is diverted to the Tis Abay hydropower stations. To ensure a TBF over the Falls, for thebaseline scenario the location of the TBF requirement was moved from immediately below the dam to the location of the waterfall.
22
lake water levels was analyzed to determine thenumber of months where the mean water level wasless than 1,785 masl (i.e., the minimum requiredfor shipping) over the 36 years of simulation.
For unmet demand, the data were summed tocalculate the annual unmet demand for each of the 36years of simulation. Since the frequency of occurrenceof unmet demand is of more interest to planners thanthe mean annual unmet demand, standard frequencyanalyses were conducted to determine the returnperiods for different magnitudes of shortfall. Thisinvolved fitting a statistical distribution (i.e. a two-parameter log-normal equation) to each time series ofannual unmet demand. The results were thenconverted to assurance levels (i.e., volumes of waterthat can be guaranteed with different degrees ofcertainty). For each return period estimated, this wasdone by subtracting the shortfall from the demand (i.e.,to give the volume that could be guaranteed) andconverting the return period to a level of assurance. Forexample, return periods of two, five and 100 yearscorrespond to assurance levels of 50, 80, and 99%,respectively. For hydropower, the volumes of unmetwater demand were converted to shortfalls in electricityproduced, so that assured levels of electricitygeneration (i.e., GWhy-1) could be computed.
There is always some uncertainty associatedwith fitting statistical distributions. In this study thiswas particularly the case for those series in whichfailure to meet demand occurred in only a fewyears of the 36-year series. Consequently, theassurance levels are not precise, but in each caseare indicative of the probability of satisfying demandin any year.
Simulation Results
Figure 10 presents a comparison of the time seriesof simulated lake levels for all scenarios with thenatural condition, both with the downstream TBF
and the VEF included. Table 8 summarizes theresults of each scenario. The results indicate thedecline in mean annual lake levels, andconsequently lake area, as water resourcesdevelopment in the catchment increases.
As would be expected, the greatest impact ofthe water resources development occurs during drycycles, in particular, from years 8 to 14 and, mostsignificantly, from years 20 to 29 of the simulation.During these periods, even without VEF releases,lake water levels are, depending on thedevelopment scenario, up to 0.82 and 1.76 mlower than natural levels in the dry and wetseason, respectively (Figure 10).
As water resources development increasesthere are longer periods of time when meanmonthly lake levels are below 1,785 masl (Table8). Under natural conditions lake levels neverdropped below this level. Under current conditions(BS), they exceed this level in 88% of the months.In the ODS, this will increase to 90%. Theimprovement occurs because the total demand ofthe Beles power station and Koga irrigationscheme (i.e., 3,047 Mm3y-1) is slightly less thancurrent demand of the Tis Abay power stations(i.e., 3,469 Mm3y-1). However, when the additionalirrigation schemes become operational, lake waterlevels will decline. In the FDS, even without theVEF releases, water levels exceed 1,785 masl just78% of the time (Table 8). In some drier years (i.e.,years 20 to 28) they hardly exceed this level inany month (Figure 10d).
In comparison to the TBF, the VEFrequirements, because they necessitate more waterflowing over the Falls, exacerbate the drop in lakewater levels in all scenarios. In the current situation(BS), the VEF would result in water levels beingabove 1,785 masl just 75% of the time (c.f. 88% withTBF). In the FDS with VEF, water level exceeds1,785 masl just 60% of the time and the mean lakearea is reduced from 3,080 to 3,023 km2 (Table 8).
23
1,783
1,784
1,785
1,786
1,787
1,788
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35
Lake
leve
l (m
asl)
Year
Natural BS with TBF BS with VEF
1,783
1,784
1,785
1,786
1,787
1,788
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35
Lake
leve
l (m
asl)
Year
Natural ODS with TBF ODS with VEF
1,783
1,784
1,785
1,786
1,787
1,788
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35
Lake
leve
l (m
asl)
Year
Natural LDS with TBF LDS with VEF
(a) (b)
(c)
FIGURE 10. Comparison of simulated and natural (observed) lake levels over 36 years with the TBF and the VEF for eachscenario. Scenarios are: a) BS, b) ODS, c) LDS, and d) FDS.
1,783
1,784
1,785
1,786
1,787
1,788
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35
Lake
leve
l (m
asl)
Year
Natural FDS with TBF FDS with VEF
(d)
Table 9 presents the estimates of irrigationwater that can be supplied at different levels ofassurance in each of the scenarios. The resultsindicate that, as would be expected, as the levelof water resources development increases (i.e.,there are more dams built) the amount of waterthat can be supplied for irr igation at lowassurance levels increases. The results alsoindicate that, again, as would be expected, lesswater can be delivered at higher levels ofassurance. This simply means that, in years oflower rainfall and hence lower flow in the rivers,less water is available for irrigation. The resultsshow that in years of very severe drought (e.g.,
approximately once in a 100 years) almost nowater would be available for irrigation. Between theLDS and FDS, the increase in irrigated arearesults in a decrease in the amount of water thatcan be supplied at high levels of assurance. Theresults also show the degree to which, in allscenarios, implementation of the VEF reduceswater availability for irrigation (i.e. from 1% to68%). The VEF has a greater impact, both athigher levels of assurance and higher levels ofdevelopment.
Table 10 presents the estimates of electricitythat can be generated with different levels ofassurance in each of the scenarios. These
24
TAB
LE 8
. S
umm
ary
of s
imul
atio
n re
sults
for
eac
h sc
enar
io w
ith m
inim
um m
aint
enan
ce f
low
and
var
iabl
e en
viro
nmen
tal f
low
s.
Sce
nario
TB
F
V
EF
Mea
n w
ater
Mea
n la
keM
ean
pow
erM
ean
irrig
atio
n%
tim
e th
atM
ean
wat
erM
ean
lake
Mea
n po
wer
Mea
n irr
igat
ion
% t
ime
mea
nle
vels
(m
asl)
area
(km
2 )ge
nera
ted
wat
er s
uppl
ied
mea
n w
ater
leve
ls (
mas
l)ar
ea (
km2 )
gene
rate
dw
ater
sup
plie
dw
ater
lev
elG
Why
-1M
m3 y
-1le
vel
exce
eds
GW
hy-1
Mm
3 y-1
exce
eds
1,78
51,
785
mas
l+m
asl
Nat
ural
1,78
6.1
3,08
016
*0
100
1,78
6.1
3,08
016
*0
100
BS
1,78
5.9
3,07
044
50
881,
785.
63,
045
333
075
OD
S1,
786.
03,
077
2,24
755
901,
785.
93,
067
2,22
554
89
LDS
1,78
5.7
3,05
72,
207
548
811,
785.
43,
034
2,17
853
766
FD
S1,
785.
63,
049
2,19
867
778
1,78
5.2
3,02
32,
134
644
60
Not
e: + 1
,785
mas
l is
the
min
imum
lev
el r
equi
red
for
ship
ping
* hy
drop
ower
pro
duce
d by
Tis
Aba
y-I
pow
er s
tatio
n by
div
ertin
g un
regu
late
d flo
w
25
estimates confirm that far more electricity isgenerated through implementation of the TanaBeles transfer than is currently produced fromthe Tis Abay power stations. The results showthat in the ODS with the TBF, 1,903 GWhy-1 canbe generated with 99% assurance (i.e., lesswould be generated on average only once every100 years). This compares to a firm energy
estimate of 1,866 GWhy-1 (Salini and Mid-day2006). Firm energy is normally defined as thatwhich can be guaranteed at an assurance levelof 99.5%. Hence, this indicates that the resultsfrom the WEAP model are comparable with thosederived in the system design and so add to theconfidence that the WEAP model simulation isreasonable.
TABLE 9. Comparison of scenarios: irrigation water that can be supplied at different levels of assurance (Mm3).
Assurance BS ODS LDS FDS
level (%) TBF VEF TBF VEF TBF VEF TBF VEF
50 - - 59 58 561 540 687 645
80 - - 54 52 475 440 575 510
90 - - 47 44 397 353 471 391
96 - - 34 29 272 217 296 208
98 - - 20 14 159 96 147 47
99 - - 1 - 26 - - -
TABLE 10. Comparison of scenarios: electricity that can be generated at different levels of assurance (GWhy-1).
Assurance BS ODS LDS FDS
level (%) TBF VEF TBF VEF TBF VEF TBF VEF
50 439 392 2,154 2,138 2,088 2,043 2,108 2,111
80 426 340 2,089 2,040 1,996 1,954 2,009 1,992
90 417 299 2,045 1,967 1,937 1,896 1,938 1,904
96 404 239 1,989 1,869 1,861 1,824 1,845 1,784
98 394 189 1,946 1,791 1,805 1,771 1,773 1,687
99 384 135 1,903 1,709 1,748 1,718 1,698 1,659
Table 10 shows that as irrigation in the LakeTana Basin increases, even though electricitygeneration is given the higher priority, thereliability of generation declines. Thus, in theLDS and the FDS, electricity generation at the99% assurance level decreases to 1,748 GWhy-
1 and 1,698 GWhy-1, respectively, under the TBFrequirement. This is the consequence of reduced
inflows to Lake Tana as a result of the increasedirrigation. The results also show the degree towhich implementation of the VEF further reducesthe reliability of electricity generation in allscenarios. As with irrigation, the VEF has agreater impact on electricity generation, both athigher levels of assurance and at greater levelsof development.
26
Discussion
Current Situation
By contributing to a significant proportion of thecountry’s electricity, the Chara Chara Weir hascontributed to the development of Ethiopia andbrought significant benefits to many people.However, the construction of the Chara Chara Weirand its operation has also had an impact on thenatural and social landscape of the Lake Tanacatchment and upper reaches of the Abay River.The changes caused by the dam have affected thecustomary and de facto entitlements to naturalresources, environmental quality and socioculturalintegrity experienced by communities living bothupstream and downstream of the dam. Whilstsome people have gained the dam has broughthardship to others. To date, the needs of thoseadversely affected have, for the most part, beeninadequately considered in decision-makingprocesses.
The operation of the Chara Chara Weir hasincreased interannual variability in lake levels.Increased drawdown in the dry season, mostsignificantly in 2003, resulted in the desiccation ofmany areas that were permanently inundatedpreviously. This has caused the loss of aquaticvegetation, including most significantly papyrusreeds, on which the Negede people depend.Although this has not been scientifically confirmed,this may have also contributed to a decline infisheries, since the reeds provide both breedinghabitat and refugia for fish. In 2003, the disruptionto shipping, as a result of the reduced waterlevels, had significant economic and socialimplications for many of the people who live on theislands and around the lakeshore.
Although there have been no detailedecological studies, the reduction in flows in thereach containing the Tis Issat Falls will mostlikely have had adverse ecological impacts.Although the average annual total flow over thefalls exceeds the DRM estimated f lowrequirement, the flow during many months isconsiderably lower than the minimum estimatedrequirement. In this study, by selecting a C/D
management classification for the reach, theimportance of electricity for the socioeconomicdevelopment of the country is recognized. A C/Dclassification recognizes that, in the interests ofEthiopia’s development, it is necessary to modifythe river from its natural condition. However, forreasons of equity and sustainability, it is stillnecessary to maintain the basic ecosystemfunctions of the river. If flows are changed toomuch, the lotic system wil l be modif iedcompletely with major loss of natural habitat andthe destruction of basic ecosystem functions. Thiscould have long-term consequences, not only forbiota but also for people living in the area. It is,therefore, necessary to derive an adequatecompromise between the ecologicalcharacteristics of the river and the level of directhuman utilization. The current planning for futuredevelopment should provide the opportunity toconsider how the basic ecosystem functions ofthe river can be safeguarded, even if this meansforegoing some electricity and irrigation.
The accuracy of the results from the DRMcannot be substantiated without further study.Given that it is underpinned by empirical equations,developed specifically for South Africa, and is onlyintended to be a “low-confidence” approach, theresults must be treated with caution. However, inthe absence of quantitative information on therelationships between flow and the ecologicalfunctioning of the river ecosystem, it provides avaluable estimate of environmental flowrequirements in the upper reach of the river. Toimprove the environmental flow estimates, detailedstudies need to be undertaken to investigate theecological sensitivity of the river to flow modificationthroughout its length - from the Lake Tana outlet tothe Falls and, indeed, downstream from this pointonwards.
Future Development
The analyses conducted in this study quantifysome of the possible impacts arising from future
27
water resources development in the catchment. Inthe past, the water level of the lake was affectedprimarily by variation in rainfall (Kebede et al.2006). Results of the simulations indicate thatanthropogenic activities are the major control nowand increasingly will be in the future.
If the full development scenario in the Lake Tanacatchment is implemented, approximately 3,600Mm3y-1 of water will be diverted for hydropower andirrigation schemes. As a result, the mean annualwater level will be lowered by 0.44 m and there willbe prolonged periods of several years, during whichwater levels will be much lower than they would benaturally. Furthermore, the average surface area ofthe lake will decrease by 30 km2 (i.e., 3,000 ha). Insome years, this will be reduced by as much as 81km2 (81,000 ha) during the dry season. This is likelyto have significant impacts on the ecology of thelake, particularly in the littoral zone and in thewetlands around the shore.
The experience of 2003, when farmersextended crop production onto the lake bed,indicates that lower water levels will almostcertainly result in people moving both cultivationand grazing onto the dried lake bed. This wouldexacerbate adverse impacts on near-shorevegetation and could increase sedimentation in thelake. Moreover, during periods of several years ofdrawdown (as occurs during dry years 20 to 29 inthe simulation), it is possible that people wouldmove their homes onto the waterless lake bed,maybe to be closer to cultivated fields. In such asituation, rapid rises in lake levels could bedisastrous, threatening both livelihoods and houses.To avoid this, it will be necessary to educate localpopulations about lake-level changes.
Lower water levels, particularly in the dryseason, will have a negative impact on navigation.Since the livelihoods of many people depend onshipping, strategies need to be developed tomitigate these impacts. These could includemodification of ports as well as the shipsthemselves to enable them to operate at lowerwater levels.
The results show that as future irrigationincreases, even though hydropower is given ahigher priority, assured supplies for electricitygeneration will reduce. Although decisions
concerning water allocation should not be guidedby economic concerns alone, economic valuationcan help to guide allocations by providing acommon point of reference and highlighting trade-offs between competing needs (Turner et al. 2004).Consequently, it would be extremely beneficial fora future study to undertake a detailed analysis ofthe economic implications of increased irrigationversus the reduced reliability of electricitygeneration. For completeness such an assessmentshould also include planned irrigation schemes inthe Beles catchment.
The results indicate that the allowance for VEFover the Tis Issat Falls reduces the availability ofwater for both hydropower and irrigation, andcauses increased drawdown of the lake. In theFDS, the VEF reduces the average lake levels byan additional 0.37 m and the average surface areaof the lake by an additional 26 km2 (i.e., 2,600 ha).This is over and above the reductions resultingfrom the TBF and will certainly exacerbate theadverse environmental and social impacts arisingfrom drawdown of the lake. Therefore, a potentialtrade-off exists between the lake ecosystem andthe ecosystem of the upper Abay River and theFalls. Since the livelihoods and well-being of manypeople are directly dependent on the ecologicalcharacteristics of both ecosystems, carefulconsideration needs to be given to determining howthe water is best utilized. This requires much moredetailed analyses of both the environmental andsocial consequences of water allocation patternsand very careful assessment of the implications forthe livelihoods of the poor.
In this study, no consideration was given to thepossible impacts of climate change. Currently, thereis great uncertainty about the likely impacts ofclimate change in the Abay Basin and in Ethiopia ingeneral. Results from Global Climate Models (GCMs)are contradictory; some show increases in rainfallwhilst others show decreases. A recent study of 17GCMs indicated that precipitation changes between-15 and +14% which, compounded by the highclimatic sensitivity of the basin, translated intochanges in annual flow of the Abay at the Sudanborder between -60 and +45% (Elshamy et al. 2008).Kim et al. (2008) found a generally increasing trendin both precipitation and runoff in the northern part of
28
the basin. Other studies have found a decline in therunoff into Lake Tana (Shaka 2008). To date, nostudies have been conducted into the possiblechanges in water demand arising from changes intemperature and rainfall in the Lake Tana catchment(e.g., for irrigation).
The water resources of the Lake Tanacatchment are highly vulnerable to changes inrainfall and hence runoff (Kebede et al. 2006). Thelack of certainty in trends in rainfall and runoffgreatly complicates water resources planning and
Concluding Remarks
Whilst acknowledging the significant contributionthat the Chara Chara Weir has made to thesocioeconomic development in Ethiopia, and hencepoverty alleviation, the results of this study haveprovided some indication of the ecological andsocial costs of both current and likely future waterresources development in the basin. Althoughlargely unreported, there is no doubt that operationof the Chara Chara Weir and diversions of water tothe Tis Abay power stations, have, in common withalmost all infrastructure development, resulted insome negative environmental and social impacts.This information may not have been available todecision-makers in the past, but disregarding thesedetails distorts the true economic costs ofdevelopment and also reduces the scope forsuccessful mitigation.
In future, there is significant potential for furthersocioeconomic development based on increasedutilization of water in the catchment. However, greatcare is needed to ensure that such development issustainable and does not adversely impact thosecommunities that depend on the natural resourcesof the lake and the rivers that feed into it. Thepredicted drop in average water levels of 0.44 m,and much more in prolonged dry periods, couldhave significant adverse ecological and social
management in what is already an uncertainenvironment. Climate change means thatstationarity (i.e., the idea that flows fluctuatewithin an unchanging envelope of variability) canno longer be assumed and necessitates that allfuture water resources development is adaptable.Further research is needed to improve quantitativeunderstanding of the impacts of climate change onwater resources and to fulfil the pragmaticinformation needs of water managers anddecision-makers.
consequences. In order to make informeddecisions about the desired ecological state of thelake and the upper reaches of the Abay River, verydetailed environmental and social impactassessments must be conducted. To becomprehensive, such evaluations must go beyondsimple cost-benefit analyses and also includeintangible benefits that cannot be expressed inmonetary terms. It is also important that decision-making processes facilitate the involvement of localpeople in order that their concerns can beadequately addressed.
This study has highlighted the value ofintegrated approaches to assessing the impacts ofplanned development. Wise management of waterresources requires decision-makers to makedifficult choices that balance the needs of nationaldevelopment with the needs of local people.Research can be useful in contributing to thedecision-making process by highlighting theconsequences, including trade-offs, associated withdifferent options. Hence, such research has animportant role to play in determining how waterresources development can best contribute toobtaining reliable and sustainable sources of water,food and energy, whilst simultaneously avoiding andmitigating harmful impacts.
29
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IWMI Research Reports
134. Evaluation of Current and Future Water Resources Development in the LakeTana Basin, Ethiopia. Matthew McCartney, Tadesse Alemayehu, Abeyu Shiferawand Seleshi Bekele Awulachew. 2010.
133. Mapping Drought Patterns and Impacts: A Global Perspective. Nishadi Eriyagama,Vladimir Smakhtin and Nilantha Gamage. 2009.
132. Malaria Transmission in the Vicinity of Impounded Water: Evidence from theKoka Reservoir, Ethiopia. Solomon Kibret, Matthew McCartney, Jonathan Lautzeand Gayathree Jayasinghe. 2009.
131. Implementing Integrated River Basin Management: Lessons from the Red RiverBasin, Vietnam. François Molle and Chu Thai Hoanh. 2009.
130. Economic Gains of Improving Soil Fertility and Water Holding Capacity with ClayApplication: The Impact of Soil Remediation Research in Northeast Thailand.Rathinasamy Maria Saleth, Arlene Inocencio, Andrew Noble and SawaengRuaysoongnern. 2009.
129. Adaptive Water Resource Management in the South Indian Lower Bhavani ProjectCommand Area. Mats Lannerstad and David Molden. 2009.
128. Importance of Irrigated Agriculture to the Ethiopian Economy: Capturing the DirectNet Benefits of Irrigation. Fitsum Hagos, Godswill Makombe, Regassa E. Namaraand Seleshi Bekele Awulachew. 2009.
127. Drivers and Characteristics of Wastewater Agriculture in Developing Countries:Results from a Global Assessment. Liqa Raschid-Sally and Priyantha Jayakody.2008.
126. Climate Change Impacts on Hydrology and Water Resources of the Upper BlueRiver Basin, Ethiopia. Ungtae Kim, Jagath J. Kaluarachchi and Vladimir U.Smakhtin. 2008.
125. The Lower Krishna Basin Trajectory: Relationships between Basin Developmentand Downstream Environmental Degradation. Jean-Philippe Venot, Bharat R.Sharma and Kamineni V. G. K. Rao. 2008.
124. Institutions, Impact Synergies and Food Security: A Methodology with Resultsfrom the Kala Oya Basin, Sri Lanka. Rathinasamy Maria Saleth, Ariel Dinar,Susanne Neubert, Bandi Kamaiah, Seenithamby Manoharan, SarathAbayawardana, Ranjith Ariyaratne and Shyamalie de Silva. 2007.
Matthew McCartney, Tadesse Alemayehu, Abeyu Shiferaw and Seleshi Bekele Awulachew
Evaluation of Current and Future Water Resources Development in the Lake Tana Basin, Ethiopia
134
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