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

3

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?

7

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

8

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?