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Water: Green Infrastructure

Build Green Infrastructure to Manage Flood Risk

Street flooded after a storm
Why Green InfrastructureHow to Resources
Why Green Infrastructure
Heavy downpours have already increased in frequency and intensity in the last 50 years, and are expected to become still more frequent and intense as global temperatures continue to rise.[1][2] Consequently, flood risk is likely to increase dramatically across the United States. The average 100-year floodplain is projected to increase 45 percent by the year 2100, while the annual damages from flooding are predicted to increase by $750 million.[3][4] Among the types of flooding that will likely become more frequent are localized floods and riverine floods. Localized flooding happens when rainfall overwhelms the capacity of urban drainage systems, while riverine flooding happens when river flows exceed the capacity of the river channel.

By reducing stormwater runoff and protecting floodplains, green infrastructure can help manage both localized and riverine floods. In areas impacted by localized flooding, green infrastructure practices absorb rainfall, preventing water from overwhelming pipe networks and pooling in streets or basements.[5] Green infrastructure practices that enhance infiltration include rain gardensbioswales, and permeable pavements. In areas impacted by riverine flooding, green infrastructure, open space preservation, and floodplain management can all complement gray infrastructure approaches. These practices reduce the volume of stormwater that flows into streams and rivers, protecting the natural function of floodplains, and reducing the damage to infrastructure and property.

Menomonee River Green Infrastructure Project manages runoff on a former brownfield site
How To
Localized Flooding: Communities may want to conduct hydrologic and hydraulic (H&H) modeling to identify a set of green and gray infrastructure practices that will meet desired flood reduction and water quality goals. For example, the Capitol Region Watershed District, located in Ramsey County, Minn., developed an H&H model to select a set of green infrastructure practices that would address localized flooding and phosphorus loading. The selected practices included rain gardens, underground infiltration trenches, an underground storage and infiltration system, and a regional stormwater pond.[6] Monitoring of these practices demonstrated their effectiveness, with all practices but the regional stormwater pond reducing runoff volumes by 99-100 percent.[7] The green infrastructure approach was also less costly than an alternative all gray infrastructure approach (estimated cost of $2.0 million compared to $2.5 million for a new 60 inch diameter storm sewer pipe[8]).

Riverine Flooding: Communities may want to conserve land in or around the floodplain to manage riverine flooding. Geographic-information-based models can help estimate the flood damage benefits of green infrastructure, compare these benefits to the cost of conservation, and target investments in conservation towards the most cost-effective areas.[9] When preserving open space throughout a watershed, communities may want to target areas with water-absorbing soils in regions experiencing high growth. In Milwaukee, for example, the Milwaukee Metropolitan Sewerage District (MMSD) partnered with The Conservation Fund to protect land meeting these characteristics. As of 2013, the program, known as Greenseams, had protected over 2,700 acres of land capable of storing an estimated 1.3 billion gallons of water.[10] By protecting this land MMSD reduced future flows and contaminants into receiving rivers and mitigated future flooding.

Mother and child planting a tree
Reducing Damage from Localized Flooding: A Guide for Communities (PDF) (180 pp, 9MB, About PDF) Exit EPA Disclaimer – This guide produced by FEMA is intended to help local offices in cities, towns, villages, and counties in the United States understand what they can do to reduce the damage, disruption, and public and private costs that result from the shallow, localized flooding that occurs within their jurisdictions.

A Flood of Benefits – Using Green Infrastructure to Reduce Flood Risk Exit EPA Disclaimer – Green infrastructure approaches can include restoration or conservation of forests, wetlands, rivers and floodplains. This report describes how these techniques and approaches can reduce flood risk for people while supporting a diverse array of other benefits.

Strategically Placing Green Infrastructure: Cost-Effective Land Conservation in the Floodplain Exit EPA Disclaimer – This paper estimates the avoided flood damages and the costs of preventing development of floodplain parcels in the East River Watershed of Wisconsin’s Lower Fox River Basin. The analysis demonstrates how any flood-prone community can use a geographic-information-based model to estimate the flood damage reduction benefits of green infrastructure, compare them to the costs, and target investments to design cost-effective nonstructural flood damage mitigation policies.

Rain Garden Reserve (PDF) (2 pp, 2MB, About PDF) Exit EPA Disclaimer – This case study from the City of Cuyahoga Falls, Ohio demonstrates the use of a series of rain gardens to mitigate localized flooding. The 24,000 square foot park drains an approximately three acre residential area and enhances outdoor recreational opportunities for the community.

EnvisionTM Sustainable Infrastructure Rating System – Business Case Evaluator (BCE) for Stormwater Exit EPA Disclaimer – A tool that includes estimates for the value of a comprehensive list of green infrastructure benefits, including reduced flooding from green infrastructure improvements. Also available from ISI here Exit EPA Disclaimer.

Economic Assessment of Green Infrastructure Strategies for Climate Change Adaptation: Pilot Studies in The Great Lakes Region Exit EPA Disclaimer – A National Oceanic and Atmospheric Administration study assessing stormwater management practices that can enable communities to reduce flooding by capturing, storing or absorbing more water from precipitation events.

Planning for Flood Recovery and Long-Term Resilience in Vermont: Smart Growth Approaches for Disaster-Resilient Communities – This report describes strategies that communities can consider to become more flood resilient, including conserving land in flood-prone areas; directing new development to safer areas; and using green infrastructure practices to manage stormwater.


1. US EPA. Climate Change Indicators in the United States. (n.d.). Retrieved July 1, 2014, from http://www.epa.gov/climate/climatechange/science/indicators/weather-climate/index.html.

2. Heavy downpours more intense, frequent in a warmer world | NOAA Climate.gov. (n.d.). Heavy downpours more intense, frequent in a warmer world | NOAA Climate.gov. Retrieved July 1, 2014, from http://www.climate.gov/news-features/featured-images/heavy-downpours-more-intense-frequent-warmer-world Exit EPA Disclaimer.

3. Jr., Inc., M. B., & LLP, D. C. (2013). The Impact of Climate Change and Population Growth on the National Flood Insurance Program Through 2100. Retrieved July 1, 2014, from http://www.aecom.com/.../Climate_Change_Report_AECOM_2013-06-11.pdf (257 pp, 12MB, About PDF) Exit EPA Disclaimer.

4. Wobus, C., Lawson, M., Jones, R., Smith, J. and Martinich, J. (2013). Estimating monetary damages from flooding in the United States under a changing climate. Journal of Flood Risk Management. doi: 10.1111/jfr3.12043. Retrieved July 1, 2014, from http://onlinelibrary.wiley.com/doi/10.1111/jfr3.12043/pdf (13 pp, 1.3MB, About PDF) Exit EPA Disclaimer.

5. Qin, H., Li, Z., & Fu, G. (2013). The effects of low impact development on urban flooding under different rainfall characteristics. Environmental Management, 129, 577-585. Retrieved July 1, 2014, from http://www.sciencedirect.com/science/article/pii/S0301479713005495 Exit EPA Disclaimer.

6. Capitol Region Water District. (n.d.) Arlington-Pascal Stormwater Project. Online resources. Retrieved July 1, 2014, from http://issuu.com/capitolregionwd/docs/arlingtonpascalbrochure_8_5x11 Exit EPA Disclaimer.

7. Capitol Region Water District. (March 2012). BMP Performance and Cost Benefit Analysis: Arlington Pascal Project 2007-2010. Retrieved July 1, 2014, from http://www.capitolregionwd.org/wp-content/uploads/2012/09/2007_2010_BMP_Performance_MainBody.pdf (166 pp, 10.6MB, About PDF) Exit EPA Disclaimer.

8. Baker, M. (2010). BMP Performance and Cost-Benefit Analysis. Retrieved July 1, 2014, from http://mnerosion.org/wp-content/uploads/2010/10/presentation_3_24_10_baker.pdf (7 pp, 728K, About PDF) Exit EPA Disclaimer.

9. Kousky, C., Olmstead, S. M., Walls, M. A., & Macauley, M. (2013). Strategically Placing Green infrastructure: Cost-Effective Land Conservation in the Floodplain. Environmental Science and Technology, 47, 3563-3570.

10. The Conservation Fund. (n.d.).Greenseams: Milwaukee Flood Management. . Retrieved July 1, 2014, from http://www.conservationfund.org/projects/greenseams-green-infrastructure-milwaukee/ Exit EPA Disclaimer.

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