Stormwater runoff is rain that flows over the ground when it falls on roads, driveways, parking lots, roofs and other surfaces that do not allow water to soak in.
Stormwater runoff is the No. 1 cause of stream impairment in populated areas. Where rain falls on paved surfaces, a lot more runoff is generated compared to runoff from the same storm over a forest or grassland. The runoff can swiftly run to streams, wetlands and rivers. It can cause flooding and erosion and destroy wildlife habitat, even in streams.
Stormwater pollution is a critical issue for those of us concerned about the devastating effects of litter. As it flows, runoff picks up pollutants from paved surfaces such as sediment, nitrogen, phosphorus, bacteria, oil and grease, trash, pesticides and metals. These pollutants come from a variety of sources, including pet waste, fertilizer, cars, construction sites and pesticides. As the amount of impervious surface in a watershed increases, waterway health declines accordingly.
To counteract these impacts, most municipalities have adopted regulations that require management of stormwater in new developments. Stormwater management is the use of specific practices, constructed or natural, to reduce, detain, slow down or remove pollutants from runoff. The management is supposed to mimic some of the natural processes that existed before the land was disturbed.
Preserving undisturbed vegetative cover during land development is much more cost effective than destroying these features and having to construct management practices. Trees, forests and other vegetation and their associated soils are often referred to as “green infrastructure” when they are used to manage runoff instead of or in addition to pipes, pumps, storage chambers or other “hard infrastructure.”
Trees and forests improve stream quality and watershed health primarily by decreasing the amount of runoff and pollutants that reach waterways. Trees and forests capture and store rain in the canopy and releasing water into the atmosphere through evapotranspiration. In addition, tree roots and leaf litter create soil that promote the infiltration of rainwater into the soil. This helps to replenish our groundwater.
Trees and forests reduce pollutants by taking up nutrients and other pollutants from soils and water through their roots, transforming pollutants into less harmful substances. Trees also improve air quality, reduce air temperatures and create habitat for wildlife, recreation and aesthetic value.
The impact of runoff can also be minimized by increasing tree canopy over paved surfaces to increase interception of rainfall. Another way to minimize impacts is by “disconnecting” paved surfaces so they no longer drain to gutters and redirecting runoff to vegetated areas, which allows the runoff to slowly soak into the ground.
Runoff impacts all communities, but particularly counties like ours on the coast. It is up to us to reduce stormwater pollution and manage runoff. To learn more about stormwater management, go to the websites for the Environmental Protection Agency, the Center for Watershed Protection and Keep Liberty Beautiful at www.keeplibertybeautiful.org.
Swida is the director of Keep Liberty Beautiful.