Mitigation and Adaptation Strategy: Infiltrate and Attenuate Stormwater Runoff

Addressing stormwater runoff can help to reduce flooding, buffer water temperature changes, increase seepage to cool river and stream temperatures, and protect habitat in wetlands, small streams, and floodplains. Strategies include:

• Create rain gardens, vegetated buffer strips, retention basins, and infiltration catch basins to facilitate stormwater infiltration that reduces runoff and increases groundwater reservoirs that feed wetlands and small streams in periods of drought. Such groundwater reserves also provide cool water to help sustain cold water species. Rain gardens and vegetated buffers infiltrate water and provide plantings that increase ecological value and sequester carbon.
• Maintain forested areas and other permeable surfaces to slow the rate at which stormwater can reach a stream, especially in headwater portions of watersheds, which can be an effective strategy in reducing downstream flooding. In addition, forested areas are effective in infiltrating stormwater.
• Reduce runoff from developed areas by increasing infiltration.
• Maintain shade to cool streams and water bodies, especially in warm summer months.
• Develop strategies for reducing water temperature by identifying and protecting locations where relatively large quantities of groundwater seep into streams. In addition, create strategies for reducing flash drought impacts in sub-watersheds that contribute to those seepage zones. 
• Collect hydrologic data and refine models of watershed hydrology; evaluate and upgrade stormwater infrastructure to understand and predict storm water effects and risks and create a safer environment.
• Continue the NRWA water quality monitoring program. This activity has accumulated a large database of measurements of flows and water quality of the main river systems taken by NRWA volunteers. View the current NRWA River Report Card, or historic data. Combining these data with data from USGS and the National Weather Service, as well as future measurements, will be invaluable in understanding changes to date and modeling future conditions.
• Evaluate the ability of existing infrastructure to accommodate predicted future flows. View story on NRWA's project to assess culverts for wildlife passage and climate resiliency,

An Example: What is a Rain Garden? 

A rain garden has a bowl shape to collect the rain that runs off from a roof, driveway, parking area or yard. This 6 to 9 inch deep basin fills with runoff and allows it to seep into the ground in a few hours. The rain garden plants and soils filter the stormwater and cleanse pollutants that could harm water quality.

Letting the runoff soak in, rather than go into the street, replaces the groundwater that keeps streams flowing during dry times. On hot summer days, rain gardens also cool runoff from dark pavement by putting it into the ground. A constant supply of cool, clean groundwater is essential to the health of stream and pond life. 

Rain gardens are planted with flowers, shrubs, trees and grasses that are easy-to-maintain and thrive without fertilizers and pesticides. There is an array of colorful plants that can be obtained at garden centers and home improvement stores, which will provide food and habitat for wildlife.

Courtesy of the MA Watershed Coalition’s Rain Garden Guide: http://www.commonwaters.org/images/stories/pdfs/raingardn_gde.pdf

Photo at top of page: Rain garden in fair weather (left) and after a rainstorm (right), photos from Massachusetts Watershed Coalition, www.commonwaters.org. View the Coalition's Rain Garden Guide.