Economics of Green Infrastructure in Adapting to Extreme Precipitation
ERG: Arleen O’Donnell, Tess Forsell, Lauren Scott Horsley Witten Group: Nate Kelly and Kathleen McAllister
NOAA Coastal Services Center
Association of State Floodplain Managers
Army Corps of Engineers, Institute of Water Resources
Communities of Toledo Ohio and Duluth, MN
Minnesota Sea Grant
American Rivers
Great Lake Pilot Projects: Duluth and Toledo
• Duluth - damages from rarer, high intensity events • Toledo - damages from frequent, low intensity events
Duluth, MN
Toledo, OH
Trends in the Great Lakes
• Experiencing precipitation more as rain, less as snow
• Projecting more intense precipitation in short durations, with extended periods of drought
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Sidewalk Superintendent Assessing Damages
After the Sun Comes Out…
$55 million in costs for approximately 700 repair jobs from one storm event in 2012
We can’t afford to keep doing this
Communities interested in using green infrastructure to help reduce flooding,
but need to know…
• What are the options?
• What do they cost?
• What benefits do they provide?
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Project Objectives
• Identify green infrastructure flood reduction options and the costs and benefits of these options
• Create an approach to inform decisions about future infrastructure investments
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HOW MODELS WERE USED
•Historical climate data
• Projected climate data
CREAT
•Peak flow
•Runoff volume
•Base flood elevation
H&H Flood
damage costs
HAZUS
$
3. Estimate flood damages
Future land use
Damages to buildings, infrastructure, recreation, land
=
Scenarios: Estimate Flood Losses
2. How much runoff? 4. Losses
Current land use
1. How much rain? Historical Future
Scenarios: Estimate Flood Reduction
1. Rain
Historical Future
2. How much runoff with green infrastructure?
3. Estimate flood damages to buildings
Costs = green infrastructure implementation and maintenance ($)
Benefits = reduced damages ($)
$
4. Estimate costs & benefits
Benefit of this happening less?
Benefit of less homes damaged?
Benefit of being able to use the park?
Benefit of not having to fix damaged land?
What Did the Modeling Show Us?
• The probability that Duluth will experience damage from 100 year storm events will nearly double based on future growth (increased runoff) and future precipitation in 20 years
• Next Question: How can green infrastructure help reduce damage?
GI Cost
Change in Flooding
Overall Storage
GI Options What are the feasible GI options for the watershed?
What is the amount of storage desired to reduce flooding?
How does flooding change if the desired GI storage is implemented?
What would it cost to get the storage we need using different types of GI?
Our Approach to Assessing GI
Target: reduce peak discharge by
20% DULUTH
How much green infrastructure storage is needed to reach this target?
76 acre-feet (current conditions) 86 acre-feet (future conditions)
Green Infrastructure
GI Options
Permeable/porous pavement
Bioretention
Blue roof
Extended detention wetland
Retention pond
Underground storage
Stormwater tree trench
Green roof
What and how much of each?
GI Unit Costs
Green Infrastructure Practice
Capital Cost per Square Foot ($/SF)
Capital Cost per Cubic Foot ($/CF)
Annual O&M Cost per Square Foot ($/SF/year)
Annual O&M Cost per Cubic Foot ($/CF/year)
Bioretention 26.0 21.2 0.9 1.3
Blue Roof 4.0 6.0 0.2 N/A
Permeable Pavement (sidewalk)
7.6 16.8 0.02 N/A
Underground Storage
N/A 41.3 N/A 1.3
Stormwater Tree Trench
7,500 per unit N/A N/A N/A
Retention Pond 1.0 2.9 0.1 0.0
Extended Detention Wetland
2.6 1.3 0.03 N/A
GI Unit Costs
Capital Cost per Cubic Foot of Flood Storage Provided ($/CF)
Most Expensive $$$$ Underground Storage
Bioretention
Permeable Pavement
Blue Roof
Retention Pond
Least Expensive $ Extended Detention Wetland
Hypothetical Cumulative Costs
Green Infrastructure Practice
Capital Cost per Cubic Foot ($/CF)
Potential Storage Volume (CF)
Estimated Cost (over 20 years)
Bioretention 21.2 1,000,000 $21,200,000
Blue Roof 6.0 150,000 $900,000
Permeable Pavement (sidewalk)
16.8 50,000 $840,000
Retention Pond 2.9 1,000,000 $2,900,000
Extended Detention Wetland
1.3 1,100,000 $1,430,000
TOTAL 3,300,000 CF (75.8 acre-feet)
$27,271,000
What are the Benefits?
Change in Flooding
How does flooding change if the desired GI storage is implemented?
Hazus estimated approximately:
• 38% fewer buildings damaged
• 27% monetary reduction in building damages
Benefits (Loss Reductions, over 20 years)
Loss Type Benefits
Structure Damage (Hazus) $1,011,887
Recreational Use $357,279
Land Restoration $290,208
Storm Sewer Infrastructure $136,640
Total $1,796,014
What We Did Not Estimate
• Co-Benefits of Green Infrastructure – Increased property values
– Ecological benefits
– Improved water and air quality
• Comparison of Costs to Gray Infrastructure
• Reduced Damages to Public Infrastructure – Roads, bridges, sidewalks, (recall $55 Million from one storm)
– Utilities (power, communications, water, wastewater)
Lessons Learned
• Develop site selection criteria in advance
• Adequate data sets, previous modeling, previous flooding damage costs)
• Need fuller assessment of benefits or GI will be shortchanged
• Examine economics over longer period of time
• Examine other methods (velocity reduction, stormwater runoff regulations) in combination with GI storage
Duluth Next Steps
• Longer timeframe to show benefits exceed costs
• Sequence GI to coincide with other capital projects for economies of scale/reduced marginal costs (using stormwater fees for implementation)
• Track local costs/benefits of GI implementation
• Assess changes to stormwater and land use policies to avoid future impacts
• Explore velocity-reduction options
Project Next Steps
• Develop user-friendly step-by-step process guide for others to use
• Try methodology in different geographies, with different climate issues and different climate impacts
• Try to quantify more benefits
• Adjust methodology accordingly
Questions?