What is the impact of impervious surfaces on stormwater runoff?

Impervious surfaces have a significant impact on stormwater runoff primarily because they prevent water from infiltrating the ground. This leads to an increase in both the volume and velocity of runoff. When rainwater falls on impervious surfaces such as roads, sidewalks, and rooftops, it cannot soak into the soil. As a result, it flows over these surfaces and collects in storm drains or directly into water bodies, increasing the overall quantity of water that enters the drainage system.

The increase in runoff volume means that more water reaches streams and rivers in a shorter amount of time, often leading to flooding and higher peak flows. Additionally, the higher velocity of the runoff—caused by its rapid movement across hard surfaces—can exacerbate erosion in downstream areas. This erosion can lead to sedimentation in waterways, negatively affecting aquatic ecosystems and water quality.

Overall, the presence of impervious surfaces disrupts the natural hydrological cycle, leading to increased runoff volume and velocity, which in turn contributes to elevated erosion rates. Understanding this relationship is crucial for implementing effective stormwater management and erosion control practices.