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Green Infrastructure – Cost Effectiveness at Different Scales
Franco Montalto, P.E. PhD
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Low Impact Development in Houston, TXRice University, February 26, 2013
1767 2013
Gowanus CanalBrooklyn, NY
Superfund site10 CSOs on the canal1.1 million m3/y (290 MGY)50 events per year
Montalto et al 2007
Research Question
Can LID cost-effectively reduce CSOs to the Gowanus Canal?
4
Observation #1
For property owners, LID retrofits appeared more
expensive than conventional building improvements
5
Standard Turf
Rain Garden
Lower Cost Option
Total Initial Cost $84 $2,800 Standard Turf
Annual O&M Cost $36 $136 Standard TurfTotal Present Value
(discounted LCC including initial, periodic and salvage value) $649.06 $978.67 Standard Turf
Rain garden is more expensive in terms of initial, O&M, and TPV
Data derived from : 2009 Green Values National Stormwater Calculator (greenvalues.cnt.org), WERF tool, considering 50 year planning period
Turf vs Rain Garden(20 ft x 20 ft patch of private property)
Porous vs. Ordinary Concrete Sidewalk (500 ft x 10 ft segment of public ROW)
Porous pavement is more expensive in terms of initial, O&M, and TPV
Data derived from : 2009 Green Values National Stormwater Calculator (greenvalues.cnt.org), WERF tool, considering 50 year planning period
Standard Sidewalk
Porous Concrete
Lower Cost Option
Total Initial Cost $25,950 $30,000 Standard
Annual O&M Cost $145 $800 StandardTotal Present Value
(discounted LCC including initial, periodic and salvage value) $24,781 $50,803 Standard
Observation #2
New policies, cost-sharing arrangements, and/or
incentives will be necessary for LID to be widely implemented.
Sample Policy* (with carrots)• Local water utility provides grant to private
property owners to install LID on their property
• Grant amount = difference in life cycle costs between the LID and conventional surface
ex: homeowner pays for conventional roof but gets a green roof
* Most water utilities today are focusing LID investments on public ROW, not private property. LID on private property most often comes about through smaller grants or new regulations.
LID ScenariosOH007 sewershed, Gowanus Canal
Montalto et al 2007
0%
10%
20%
30%
40%
50%
0 10 20 30 40 50 60 70 80 90
Cost (Millions of $)
% R
educ
tion
in C
SO D
isch
arge
Small Tank
Medium Tank
Large Tank
Porous Pavements
Urban Brooks
Green Roofs
Comparison of “grey” and “green” approaches (implemented separately)
Montalto et al 2007
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10%
20%
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0 10 20 30 40 50 60 70 80 90
Cost (Millions of $)
% R
educ
tion
in C
SO D
isch
arge
Small Tank
Medium Tank
Large Tank
Porous Pavements
Urban Brooks
Green Roofs
Comparison of “grey” and “green” approaches (implemented separately)
Montalto et al 2007
Limited availability of implementation sites
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0 10 20 30 40 50 60 70 80 90
Cost (Millions of $)
% R
educ
tion
in C
SO D
isch
arge
Small Tank
Medium Tank
Large Tank
Porous Pavements
Urban Brooks
Green Roofs
Comparison of “grey” and “green” approaches (implemented separately)
Montalto et al 2007
Green roofs cost more than a small tank
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0 10 20 30 40 50 60 70 80 90
Cost (Millions of $)
% R
educ
tion
in C
SO D
isch
arge
Small TankMedium Tank
Large Tank
Porous Pavements
Urban Brooks
Green Roofs
Montalto et al 2007
Comparison of “grey” and “green” approaches (implemented together)
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10%
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0 10 20 30 40 50 60 70 80 90
Cost (Millions of $)
% R
educ
tion
in C
SO D
isch
arge
Small TankMedium Tank
Large Tank
Porous Pavements
Urban Brooks
Green Roofs
Montalto et al 2007
Comparison of “grey” and “green” approaches (implemented together)
LID appears more cost-effective
0%
10%
20%
30%
40%
50%
0 10 20 30 40 50 60 70 80 90
Cost (Millions of $)
% R
educ
tion
in C
SO D
isch
arge
Small TankMedium Tank
Large Tank
Sensitivity on Cost & Performance
Increasingly cost effective systems
Less cost effective systems
Montalto et al 2007
17
C LID System Installation Cost ($/m2) 0.1 0.3 0.5
172 194
Green Roof
215 54 / 32 65 / 43
Porous Surface (concrete/asphalt)
75 / 54 110 146
Rainwater Harvesting (unit: linear m)
183
LID is more cost effective than all tanks LID is cost effective when implemented after constructing a small tank LID is cost effective when implemented after constructing a medium sized tank LID might only be cost effective after construction of a large tank
Shading Key
LID Cost MetricLID Performance metric
Sensitivity Analysis
Urban brooks
18
C LID System Installation Cost ($/m2) 0.1 0.3 0.5
172 194
Green Roof
215 54 / 32 65 / 43
Porous Surface (concrete/asphalt)
75 / 54 110 146
Rainwater Harvesting (unit: linear m)
183
Outcome #1: LID is more cost effective than all tanks
0%
10%
20%
30%
40%
50%
0 10 20 30 40 50 60 70 80 90
Cost (Millions of $)
% R
educ
tion
in C
SO D
isch
arge
Small TankMedium Tank
Large Tank
Urban brooks
19
C LID System Installation Cost ($/m2) 0.1 0.3 0.5
172 194
Green Roof
215 54 / 32 65 / 43
Porous Surface (concrete/asphalt)
75 / 54 110 146
Rainwater Harvesting (unit: linear m)
183
Outcome #2: LID cost effective after a small tank
0%
10%
20%
30%
40%
50%
0 10 20 30 40 50 60 70 80 90
Cost (Millions of $)
% R
educ
tion
in C
SO D
isch
arge
Small TankMedium Tank
Large Tank
Urban brooks
20
C LID System Installation Cost ($/m2) 0.1 0.3 0.5
172 194
Green Roof
215 54 / 32 65 / 43
Porous Surface (concrete/asphalt)
75 / 54 110 146
Rainwater Harvesting (unit: linear m)
183
Outcome #3: LID cost effective only after med-large tanks
0%
10%
20%
30%
40%
50%
0 10 20 30 40 50 60 70 80 90
Cost (Millions of $)
% R
educ
tion
in C
SO D
isch
arge
Small TankMedium Tank
Large Tank
Urban brooks
The next generation of research questions
• Hydrologic Effectiveness: o How well will ultra-urban LID systems actually be able to
reduce runoff?
• Scaling Up: o What specific challenges need to be overcome for LID to
be cost effective at the watershed scale?
Hydrologic Effectiveness
GI Monitoring NetworkThe Sustainable Water Resource Engineering Lab at Drexel University
New York City sites Philadelphia sites
Nashville Greenstreet(Queens, NY)
Bioretention Bed #1 = 145 m2 (1560 ft2)Total catchment area = 475 m2 (5113 ft2)Hydraulic loading ratio = 3:1Curbcut inletOverflow to catchbasinLocal soils are sandy
26
Nashville GreenstreetPerformance during Superstorm Sandy
• 33 mm (1.3 in) rain measured onsite
• 147 m3 (39,000 gallons) of street and sidewalk runoff (~10x as much as expected)
Cumulative rain
Flow through flume
27
Nashville GreenstreetPerformance during Superstorm Sandy
• Negligible ponding• No overflow to sewer
2828
Nashville GreenstreetPerformance during Superstorm Sandy
• Several periods of rapid infiltration detected in lysimeter
• Virtually all of the 152 m3 (40,101 gallons) of rain and runoninfiltrated
29
Nashville GreenstreetPerformance during Superstorm Sandy
Outlier (30 cm)
• Upper soils got wet, then drained by gravity, with further evaporation during subsequent 6 day dry spell
• Very small impact on VMC below 30 cm
30
Nashville GreenstreetPerformance during Superstorm Sandy
• Small (5 cm) but detectable temporary increase in regional water table elevation
• After peak rain intensity, water table drops (as quickly as it rose)
31
Nashville GreenstreetPerformance during Hurricane Irene
• 163 mm (6.4 in) rain measured onsite
• Greater ponding depths observed
• Overflows brief• Infiltration still rapid
Cumulative rain
Ponding depth
Two brief periods of overflow
1009080706050403020100Ann
ual P
erce
nt re
tent
ion
High performance(80-100%)
Medium performance(30-80%)
Low performance(20-30%)
All monitored GreenstreetsAnnual percent retention
All Greenstreets(20-100%)
Variability due to:1) Precipitation amount &
distribution2) Inlet efficiency3) Engineered volume of
surface depressions4) Infiltration capacity5) Hydraulic loading ratio
Time (two months)
Lysi
met
er M
ass
Alley Pond Park (ecological reference)
Colfax (surrounded by curb)
Nashville (catchment:bioretention ratio = 3:1)
Greenstreet ComparisonsSite-to-site and Site-to-park
Time (two months)
Lysi
met
erM
ass
Evaporation = reduction in mass over dry spells
Nashville shows the greatest reduction in mass (e.g. accelerated evaporation)
Annual averages:Nashville 2.3 mm/dColfax: 1.96 mm/dAlley Pond: 0.58 mm/d
By irrigating with stormwater we can accelerate ET over reference conditions, (accelerating heat loss as well since 1 gm = 595 calories)
Greenstreet ComparisonsSite-to-site and Site-to-park
VegetatedCourtyard
Backyard
Urban Park
Courtesy of USDA NRCS
Other permeable surfacesConventional urban green spaces
Courtesy of Tatiana Morin
Courtesy of Tatiana Morin
Without guards With guards
Other permeable surfacesTree pits
Porous Asphalt
Porous Rubberized
Safety Materials
PorousPavers
Concrete
Porous Standard
Courtesy of USDA NRCS
Other permeable surfacesPermeable pavements
Results(n=139)
Alizadehtazi et al (in revision)
Conventional spaces (parks and tree pits without guards) displayed the lowest infiltration capacity
Porous concrete consistently presented the highest infiltration capacity
Infiltration capacity > median intensity of regional 15 minute rainfall intensity
Challenges of Scaling Up
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0 5 10 15 20 25
% re
duction in ann
ual run
off
Year
0
2000
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6000
8000
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TOTA
L CO
ST: N
PV (k $)
Year
Runoff reduction Program costModeling Performance Modeling Cost
Scale up metrics over time
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0 5 10 15 20 25
% re
duction in ann
ual run
off
Year
0
2000
4000
6000
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0 5 10 15 20 25
TOTA
L CO
ST: N
PV (k $)
Year
? ?
Uncertainty due to climate, physical performance metrics
Uncertainty due to unit costs of GI installations
Rate and extent of adoption
Runoff reduction Program cost
Scale up metrics over time Uncertainty
0
20
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% re
duction in ann
ual run
off
Year
0
2000
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0 5 10 15 20 25
TOTA
L CO
ST: N
PV (k $)
Year
? ?
Uncertainty due to climate, physical performance metrics
Uncertainty due to unit costs of GI installations
Rate and extent of adoption
Runoff reduction Program cost
Scale up metrics over time Uncertainty
0
20
40
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0 5 10 15 20 25
% re
duction in ann
ual run
off
Year
0
2000
4000
6000
8000
0 5 10 15 20 25
TOTA
L CO
ST: N
PV (k $)
Year
? ?
Uncertainty due to climate, physical performance metrics
Uncertainty due to unit costs of GI installations
Rate and extent of adoption
Runoff reduction Program cost
Scale up metrics over time Uncertainty
Stormwater wetland projects
Streetscape bioswales
Lot level strategies (planters, stormchambers, cisterns)
Square feet of catchment area
Con
stru
ctio
n C
ost
Greater catchment area, greater economy of scale
but with change in GI system typology
Stormwater wetland projects
Streetscape bioswales
Lot level strategies (planters, stormchambers, cisterns)
Square feet of catchment area
Con
stru
ctio
n C
ost
Wetland projects
Streetscape bioswales
Lot level stormwatermanagement
Square feet of catchment area
Con
stru
ctio
n co
st p
er s
quar
e fo
ot c
atch
men
t
Wetland projects
Streetscape bioswales
Lot level stormwatermanagement Greater catchment area, lower
unit costs
but with change in GI system typology
Square feet of catchment area
Con
stru
ctio
n co
st p
er s
quar
e fo
ot c
atch
men
t
0
20
40
60
80
100
0 5 10 15 20 25
% re
duction in ann
ual run
off
Year
0
2000
4000
6000
8000
0 5 10 15 20 25
TOTA
L CO
ST: N
PV (k $)
Year
? ?
Uncertainty due to climate, physical performance metrics
Uncertainty due to unit costs of GI installations
Rate and extent of adoption
Runoff reduction Program cost
Scale up metrics over time Uncertainty
Why is it hard to predict the rate and extent of LID adoption?
• Unmapped physical heterogeneities
• Institutional complexity
• Unpredictable community perceptions and potential for involvement
Unmapped physical heterogeneity
Setbackso From foundations, property lines, curbs, and underground
utilities
Subsurface conditionso Bedrock, high water table, low permeability or contaminated
soils, root systems of existing trees
Surface conditionso Parking spots and driveway curb cutso Sidewalk widths
Institutional complexity
LID in the public right-of-wayo Inter-agency coordination
LID on private propertyo Regulations for new constructiono Incentives for retrofitso Enforcement?o Impacts on water bills?
Notes from Philadelphia…
Neighborhood Statistics:Area: ~ 175 hectares10,363 lots18.5% of lots are vacant75% of lots are residential82% of surface imperviousPop: 21,20035% below poverty line82% Af. Am. 10% Asian
Residents & Resident Owners
Local NGOs & informal associations
Blocks, Streets, & Parcels
PWD
Other govtagencies
Non-resident owners &
speculators
Local institutions (churches, schools, etc)
Global agent Local agent set Reactive set
Cos
t sca
ling
Lear
ning
cur
veP
artn
ersh
ips
PWD decision sequencing (sample)
Collect information
Social network
Local conditions
Assess information
Values
Trust
Decide (stochastic)
Index
Constraints
Inform
Social network
Physical environment
Property owner decision sequencing
LID in the public right of way only
1
Frac
tion
gre
ened
Years
Target
Limited options Limited uncertainty Limited benefits
LID in the public right of way only
LID in the public right of way AND on publicly owned vacant land
1
2
Frac
tion
gre
ened
Frac
tion
gre
ened
Years
Years
Target
Target
Path dependency (early implementation of cost effective projects on vacant land spreads the money further)
Development of privately owned green infrastructure banks
Potential big winner
LID in the public right of way only
LID in the public right of way AND on publicly owned vacant land
1
2
3
Frac
tion
gre
ened
Frac
tion
gre
ened
Frac
tion
gre
ened
Years
Years
Years
Target
Target
Target
61
• Porous pavements nice, but smooth surfaces only please (for easy snow shoveling!), and cover those tree pits with gratings…
• Individual vacant lots in the middle of the block should be redeveloped; corner and clustered vacant lots should be greened
• Street trees and sidewalk planters are good, but don’t block store windows or make it difficult for motorists to see around corners!
• You want to use my backyard for what…?
• You expect who to maintain all this…?
• How do GI jobs go to the local workforce (and not outside contractors)?
• Why should I believe that this new green program be successful when other government programs have failed in making a difference?
• Who will be part of the decision making (the newcomers? Or me?)
• Are you experimenting on us? Please just fix the sewer problems!
• We have never worked together before. Why should we do that now?
• Green infrastructure…?!? We need affordable housing!
Community perceptions
62
Observation:Community dynamics could
work both for or against LID… how do we get a better handle
on this?
Mediated Modelingpremise
Involve stakeholders early
Reduce uncertainty
Build consensus
o Free and web-basedo Built in selection of 30 different LID strategies for
parcels and 16 for streetso Built-in stochastic rainfall generatoro Robust hourly water balance calculations over all rainfall
realizationso Phased life cycle costing algorithm driven by built in
database of national costs
LIDRALow Impact Development Rapid Assessmentwww.lidratool.org
Urban Hydrologic Response Units (UHRUs)
Roof
Driveway Yard
HP-009 (Bronx, NY)
GI Selector tool (parcel)
GI Selector tool (street)
LID scenarios developed with local stakeholders
1. Green roof, Rain garden, Permeable Pavement Driveway and Downspout disconnect roof to rain garden on public housing sites
2. Bio-swale and tree pits on streets3. Permeable pavement on parking lots4. Combined scenario
Sample runoff reduction results
Runoff reduction ratio per year
Annual volume of reduced runoff
Ann
ual v
olum
e of
redu
ced
runo
ff (m
3 )
Years
Sample LCC cost results (NPV)Annual expenditures during initial construction phase
Cumulative NPV of entire program to date
1st generation O&M
Ann
ual c
osts
(kila
-dol
lars
)
Cum
ulat
ive
cost
s (k
ila-d
olla
rs)
1st replacements plus O&M
Residual value of GI portfolio at year 30
HP-009 Sample ResultsRunoff reduction from ROW bioswales“Slow and Steady… “ “Get ‘em all in fast… “
Ann
ual v
olum
e of
redu
ced
runo
ff (m
3 )
Years
Ann
ual v
olum
e of
redu
ced
runo
ff (m
3 )
Years
Run
off r
educ
tion
ratio
Run
off r
educ
tion
ratio
After 30 years, both implementation strategies achieve identical runoff reduction (~2.3%), but….
HP-009 Sample ResultsProgram costs for ROW bioswales (NPV)“Slow and Steady… “ “Get ‘em all in fast… “
Years
Ann
ual c
osts
(kila
-dol
lars
)
Years
Cum
ulat
ive
cost
s (k
ila-d
olla
rs)
But at really different costs ($1.4 million vs $2.4 million) in 2013 dollars(Note: y-axes of left and right charts on different scales)
Ann
ual c
osts
(kila
-dol
lars
)
Cum
ulat
ive
cost
s (k
ila-d
olla
rs)
Concluding remarks• LID is an effective site-scale strategy for
managing stormwater (and achieving other urban sustainability goals)
• Assessing cost-effectiveness at the watershed scale, however, is non-trivial
• Recommendation: • Involve stakeholders early to achieve consensus on a
path forward. • Though the path will be uncertain (and will need to be
revised many times), all parties will feel invested, increasing certainty that a solution will be feasible
New York Daily News, 2009
