Definitions for "Impervious surfaces"
Materials like cement, asphalt, roofing and compacted soil prevent percolation of runoff into the ground.
Land surfaces such as roads, parking lots, buildings, etc. that prevent rainwater from soaking into the soil. The water increases in velocity causing more erosion; it warms causing potential heat stress for downstream trout; it picks up roadway contaminants; and the loss of vegetation removes a "sink" for dissolved nutrients - plant uptake.
Hard surfaces (rooftops, sidewalks, driveways, streets, parking lots, etc.) that do not allow rain water to infiltrate into the ground. Instead, the rain water runs off these surfaces, picking up heat and other water pollutants that can be transferred to streams, rivers, and lakes, creating water quality problems. Furthermore, these surfaces prevent rain water from infiltrating into the soil to recharge the ground water aquifers that provide spring flow to the Kinnickinnic River.