Impervious area reduction is a set of techniques employed during site planning and development stages that minimize the amount of impervious surfaces from buildings, roadways, driveways, parking areas and sidewalks. Examples may include building a residential addition up instead of out, using permeable paving materials, reducing building setbacks and clustering buildings to reduce roadway, driveway and sidewalk area. These techniques may also be used to retrofit redevelopment sites.
- Reduces the amount of runoff from developed and re-developed areas.
- Reduces pollutants and sediment in nearby waterways.
- Benefits are enhanced when combined with methods to “disconnect” impervious surfaces through the use of bioswales, filter strips, vegetated swales, etc. A few simple ways to do this include:
- Directing downspouts to vegetated, bioretention, or infiltration areas;
- Directing flows from driveways to vegetated areas;
- Breaking up flow directions from expansive paved areas;
- Encouraging sheet flow through vegetated areas; and
- Carefully locating impervious areas so that it drains as naturally as possible and runoff is minimized.
Grammenos, F. and J. Tasker-Brown. No Date. Residential Street Pattern Design for Healthy Livable Communities. Website. www.greenroofs.ca/nua/ip/ip02.htm (March 2007).
Impervious Area Effect: Federal Interagency Stream Restoration Working Group