Impervious surface is a hard surface, such as rooftops, sidewalks, and parking lots, which prevents the natural infiltration of rainwater into the ground. Pervious surfaces such as grass, trees, and other vegetation allow rainwater to infiltrate into the ground.
The more impervious surface area a property has, the more stormwater runoff it will generate. This increased stormwater runoff has a greater impact on the public drainage system. Therefore, higher SWM Utility service charges are appropriate so the county can manage the quantity and quality of that excess runoff.