Answer 5. Impervious surfaces are hard surfaces (such as rooftops, streets, parking lots, driveways, patios, asphalt, concrete, compacted gravel, and other paved areas). These surfaces prevent or limit the natural entry of stormwater into the ground. When stormwater hits an impervious surface, it runs off and does not soak into the ground. Runoff can generate high volumes of water and it flows more quickly than water flowing over a vegetated surface. Runoff and stormwater flowing quickly can cause flooding. It can also cause erosion in ditches and streams when the bare soil becomes exposed.