Impervious Surfaces Increase Runoff
Impervious surfaces are hard surfaces, such as sidewalks, streets, and rooftops, that don’t allow water to seep into the ground. Water that does not soak into the ground becomes runoff and travels to the nearest body of water.
As the amount of impervious surfaces increases, more runoff is created and less water is able to sink in, or “infiltrate,” into the ground. Infiltration is very important because water that travels slowly to creeks and streams sustains their flows through drier spells, which is good for aquatic life. Water that travels slowly through the ground also gets filtered by natural processes before it reaches the water body.
Water that travels too quickly to creeks and streams can pick up and carry a lot more sediment and other pollutants. It also hits creeks and streams in a rush, which worsens erosion and flooding.
Additional Resources
The following organizations offer more information about runoff and impervious surfaces.
Greater Milwaukee Water Quality Initiative
Environmental Science for Everybody Round the Earth
The Center for Watershed Protection
The Stormwater Managers’ Resource Center
