What is Stormwater and where does it come from?

Stormwater is any precipitation that collects in a natural or constructed storage or transport system following a storm event. For example, during construction of a new building or neighborhood, sites are often cleared and the soil is firmly compacted, which prevents rainfall or snowfall from soaking into the soil. As a result, the rainfall streams along the surface of the ground: this is stormwater runoff. After construction activities, impervious areas such as roads, roof tops, parking areas, and sidewalks prevent infiltration of moisture from rain and snowfall, thus causing stormwater runoff. This runoff can be too much for the existing natural drainage systems to handle. As a result, natural drainage systems are often altered to rapidly collect runoff and convey it away (using curb and gutter, enclosed storm sewers, and lined channels). The stormwater runoff is then discharged to downstream waters such as streams, reservoirs, and lakes.

 

How does Impervious area affect water quantity?

Impervious area creates a barrier to water soaking into the soil and prevents the rainfall or snowfall from recharging ground water supplies in that area. This reduces the amount of ground water that is available to well water users and increases the downstream surface water flow. 

Changes in Runoff Patterns

 

 

How does impervious area affect water quality?

Water that soaks into the soil is naturally filtered and cleaned. Water flowing on the surface of developed property picks up pollutants such as sediment, oil, and salts from roads and parking areas, fertilizer from lawn runoff, and bacteria from property where animals are kept. The effect of one property on the quality and quantity of stormwater runoff may seem insignificant. However, the cumulative impact from hundreds of thousands of properties across the state can negatively affect our water quality. And keep in mind: much stormwater runoff, after it enters lakes, streams, and reservoirs, or soaks into the ground, eventually becomes drinking water for downstream communities. This is one reason protecting water quality is so critical in Dougherty County.