In a natural environment, most rainwater soaks into the ground or is captured by trees and other plants. As land is developed, it is covered by hard surfaces - roads, parking lots and rooftops – that prevent natural infiltration, and allow water to quickly run downstream. This runoff, known as stormwater, carries dirt, fertilizer, pet waste, pesticides and debris into lakes, streams and wetlands. Polluted stormwater runoff is the number one water quality problem in Minnesota and across the country.
In many urban environments, stormwater is managed with storm sewer systems that quickly move stormwater away to prevent localized flooding. However, storm sewers often drain directly into lakes, streams and wetlands, rapidly carrying pollution into our valuable surface waters.
Stormwater Best Management Practices (BMPs) are the primary method for dealing with polluted runoff. BMPs may include ponds, raingardens, porous pavement, green roofs, or other practices that temporarily hold, filter, or reduce stormwater. Slowing down or reducing the flow of water minimizes flooding and reduces the amount of pollution reaching downstream water bodies.
The changes in the landscape that occur during the transition from rural and open space to urbanized land use have a profound effect on the movement of water off of the land. The problems associated with urbanization originate in the changes in landscape, the increased volume of runoff, and the quickened manner in which it moves. Urban development within a watershed has a number of direct impacts on downstream waters and waterways, including changes to stream flow behavior and stream geometry, degradation of aquatic habitat, and extreme water level fluctuation. The cumulative impact of these changes should be recognized as a stormwater management approach is assembled.