The Story of Stormwater
Stormwater Issues
When rain falls in a natural ecosystem, a significant portion of the rain is absorbed into the ground, where it either becomes groundwater or is taken up by plants. The rainfall that is not absorbed runs off into creeks, washes, rivers, lakes or the ocean. When humans develop communities, we significantly change the balance of the system by covering the land with impermeable surfaces—surfaces like rooftops, asphalt and concrete that do not allow water to sink into the ground. This change to the ground’s surface dramatically increases the amount of runoff that flows through our developed areas. This increase in runoff has two main consequences:
- Flooding: all the water that used to seep into the earth now courses through streets and into waterbodies that are not adapted to holding those volumes and rates of flow. This often causes erosion and flooding of both natural and developed areas.
- Nonpoint-source pollution: on its way over the surface, the runoff picks up everything we put on the ground—pollutants like pet waste, automobile oil/fluids, herbicides and trash that are deposited in small amounts over a large area. Stormwater carries and concentrates these pollutants in rivers, lakes, and even groundwater, causing a host of problems for people and ecosystems alike. And as our water bodies degrade, particularly our urban washes and creeks, they often become neglected eyesores that people treat as dumping grounds.
WMG works with communities to turn these problems of stormwater around through a variety of Stormwater Best Management Practices.
Stormwater Best Management Practices
Stormwater Best Management Practices (BMPs) are the best known measures that communities have to deal with issues of stormwater quality and quantity. They include practices such as street-sweeping, and structural features like water harvesting basins. BMPs improve water quality by breaking down and/or removing pollutants from stormwater; and address flooding issues by slowing, spreading and infiltrating stormwater as close to the source as possible.
BMPs work best when they are designed as a system, to be applied across a watershed or neighborhood. In many cases, they can (and should) serve many community functions beyond stormwater management, like beautifying and shading streets, slowing traffic, and creating wildlife habitat (for more on this, see Benefits of Sustainable Stormwater Management).
Some examples of BMPs include:
Curb cuts with basins or swales in the right-of-way: In existing neighborhoods or where street-side curbs are needed, curbs are cut (or designed with cut-outs) and stormwater is passively drawn into depressed basins or swales dug in the right-of-way between sidewalk and curb. Stormwater provides free, passive irrigation to street trees, shrubs and wildflowers planted in the basins; the vegetation and soil in turn help to break down pollutants in the stormwater, and allow water to sink back into the ground.
Chicanes, Traffic Circles and Medians: Chicanes are extensions of the curb out into a roadway, and both chicanes and traffic circles are used by neighborhoods to slow traffic. Medians are used to separate lanes of traffic, slow traffic, and beautify streets. The best of these devices have flush or cut curbs that allow stormwater to flow into a depressed, planted, and permeable interior. Cut or flush curbs only make sense when these devices are located at the low point in the street, which often makes medians and traffic circles the best choice for concave streets (low point in the middle), and chicanes the best choice for convex streets (low points along the sides).
Parking lot design: With huge expanses of impermeable concrete and asphalt, parking lots can contribute massive volumes of stormwater (often polluted by oil and fluid drippings from automobiles) to their local watershed. For this reason, governments usually require parking lot developers to design large basins for stormwater detention. These basins often become neglected eyesores at the back of a property. A growing preferred alternative to a single large detention area is placing earthen “micro-basins” throughout the lot that catch stormwater and use it to irrigate car-shading trees.
Permeable pavement: Unlike traditional asphalt or concrete, permeable pavements have pore spaces in them that allow stormwater to infiltrate into the ground underneath. This literally addresses stormwater at the source, in many cases not even allowing runoff to form even in large storms. Permeable pavement is a growing choice for parking lots, walkways and bikeways, and is most appropriate in areas where sediment will not wash onto the area and fill the pavement’s pores.
EPA provides a guide on green infrastructure in arid and semi-arid climates available at: http://www.epa.gov/npdes/pubs/arid_climates_casestudy.pdf
Benefits of Sustainable Stormwater Management
Neighborhood stormwater improvements can be integrated with the following community goals:
- Public safety: Crime, including graffiti, statistically decreases with neighborhood landscape improvements as neighborhoods look more “taken care of.”
- Traffic calming and neighborhood livability: Chicanes, medians, traffic circles and right-of-way improvements all help to create neighborhood streets that are safe and inviting for pedestrians and bicyclists—people—and not just cars.
- Aesthetics and wildlife: Native and low-water use plants that thrive on stormwater-based irrigation create beautiful landscapes, habitat for native birds and insects, and a unique sense of place that celebrates each community’s unique ecosystem.
- Shading streets and sidewalks and reducing urban “heat island” effects: Planting street trees and removing hardscape cools neighborhoods in hot summer months, and can help to reverse the heat island effect (phenomenon of increased temperature in urban areas as a result heat-trapping and radiating properties of concrete and asphalt).
- Increased property values: The Arbor Day Foundation has proven that homes and neighborhoods with trees have higher property values.
- Community building: By improving the outdoor environment and making streets safe for people, integrated stormwater improvements make it easier for neighbors to gather and interact. Also, many neighborhoods work with WMG and others to make stormwater improvements through volunteer workshops that build community.