Is That a Park or a Storm Sewer? Trick Question

September 26, 2007

For years civil engineers, and environmental and planning officials have used the fuzzy buzzword "green infrastructure" to describe the role that urban green spaces (such as parks and trail systems), wetlands, surrounding forests and open space, and other aspects of the natural environment play in supporting healthy communities. Lately, however, that term has gotten more specific as many cities seek more robust and cost-effective stormwater management.

The main concept is to make the urban environment and surrounding lands act more like a sponge, so that during times of heavy rainfall or snowmelt more water gets captured, held, and gradually released. This relieves peak load on channelized, structural "gray infrastructure," often the cause of overflows from combined and sanitary sewer systems (CSO and SSO events, respectively). Also, green infrastructure can help remove pollutants from stormwater runoff, thus reducing waterbody pollution by nitrogen, microbes, and toxics.

The increasing age and unreliability of US sewer systems is a big factor driving the green infrastructure movement in stormwater management (Sept. 13, 2007, USA TODAY story). Furthermore, in many communities and metro areas funds to upgrade sewer systems are hard to come by. In contrast, green space projects can attract more public and political support (and funding). And green space projects can be designed to provide stormwater management benefits - which can help prevent or minimize sewer overflows, easing loads on overburdened sewer systems. Also, green infrastructure is often easier and less costly to maintain and repair than traditional sewers, since its core components tend to be at or near the surface, not buried beneath streets or buildings.

Common green infrastructure measures used to manage stormwater include:

Conservation easements restricting land uses that would increase runoff.
Grassed swales: Vegetated runoff areas, such as beside highways.
Green parking: Reducing the contribution of parking lots to total impervious cover.
Green roofs: Soil and plant materials cut overall runoff.
Infiltration trenches: Rock-filled trench with no outlet that receives stormwater after pretreatment such as a swale. Runoff is stored between the stones and infiltrates through the bottom into the soil.
Open-space design communities: Concentrating homes in a compact portion of the development site in order to provide open space and natural areas elsewhere on site.
Porous pavement: Permeable surfaces, often with an underlying stone reservoir that temporarily stores surface runoff before it infiltrates into the subsoil.
Protection of natural features such as wetlands: If you don't destroy it, you don't have to compensate for lost functionality.
Rain gardens (bioretention): Landscaping features that provide on-site treatment of stormwater runoff, commonly located in parking lot islands, in communities, or in individual yards.
Reforestation, urban forestry, and forested (riparian) buffers: Trees can absorb and process an amazing amount of water.
Constructed stormwater wetlands: Artificial ponds that fill occasionally with stormwater, and are dry or boggy at other times.
Low-impact development (LID) practices that minimize impervious surfaces and fast runoff.
On-lot treatment such as rain barrels, cisterns, and downspout disconnections.

Details and resources on all of these strategies from EPA's green infrastructure page. Press: Jennifer Wood, 202-564-4355.

If your region suffers from sewer overflows, flooding, or contaminated waterbodies, ask whether green infrastructure measures are being used or considered for stormwater management. Local planning boards, sewer districts, water utilities, and landscape architects can be good places to start your inquiries.

Ask about measures implemented in recent years, so you can investigate their mitigation impact for recent storm or snowmelt events. That impact can be translated into hard numbers, as shown by this 2006 article from the professional journal Stormwater.

Is That a Park or a Storm Sewer? Trick Question

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