Over the past century or so we have built homes, roads, shopping centers, commercial buildings, and so on, all of which dramatically increased the amount of impervious surface. At the same time, we have modified the landscape to facilitate rapid drainage of stormwater runoff from our developments. This has had the effect of concentrating the stormwater runoff and decreasing infiltration. This causes three problems.
- Flowing water is quite powerful and picks up soils, debris, leaves, and oils from the impervious surfaces it flows over. Unless treated, this material reaches surface waters, where it can pollute them beyond the point where the water supports wildlife or recreation.
- The increased volume of water running off and the increased speed of the drainage means large quantities of water reach surface waters quickly. This can lead to flooding and scouring (erosion) of river channels.
- Less water infiltrates, resulting in reduced soil moisture and less water percolating to groundwater. Consequently, plants may be stressed during dry periods and aquifer (groundwater) levels may decrease. Depleted groundwater levels may, in turn, reduce water levels in streams and reduce drinking water supplies.
We can minimize or reduce these negative impacts through proper management of stormwater. Examples of management strategies include the following.
- Retain runoff water and release it slowly to reduce flooding.
- Capture and treat runoff to reduce pollutant loads.
- Reduce the amount of materials available to the rapidly flowing water by stabilizing slopes with ground cover and removing debris and other potential pollutants from the path of the runoff.