Stormwater: What’s the big deal?

When the amount of rain falling exceeds the land's ability to absorb it, stormwater runoff is produced. The amount of the runoff and rate at which it flows vary with the intensity and duration of the rainfall and the type of land surface upon which it falls. A short light rain falling on permeable soils might produce no runoff while heavy rain landing on a parking lot will produce a substantial amount.

As stormwater runoff moves over land, it dissolves materials or sweeps them along with its flow. Forests, fields, and other vegetated areas slow the flow of stormwater, filter out sediments, and trap pollutants or break them down in roots. Buildings, roads, parking areas, and exposed bedrock on the other hand, increase the volume and speed of stormwater runoff because these hard surfaces prevent water from absorbing into the ground and offer little resistance to slow down the flow.

Undisturbed landscape                              Developed landscape

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Anyone who has looked at local rivers and streams during a storm knows that stormwater is a transportation system for pollutants. Soil that washes off construction sites; trash, cigarette butts. and other litter that has washed from parking lots; antifreeze and oil that has dripped from cars and trucks; fertilizers and pesticides from golf courses, fields, and lawns; nutrients from agricultural operations; grit and salt from de-icing roadways: all this and more can be flushed directly into our waterways when it rains. This polluted stormwater can cause serious water-quality problems, be hazardous to human health, and affect aquatic plant and animal life in streams and lakes.

The bottom line is that as population grows, the more we alter the landscape—and the more we alter the landscape, the more we affect the natural ability of the hydrologic cycle to deal with stormwater. Besides moving more water and pollutants into waterways more quickly, human activities are also resulting in less water being absorbed for groundwater recharge.