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What is Stormwater Runoff?
Stormwater runoff is water from rain or melted snow that cannot be absorbed by the soil and instead washes off the land surface. Along the way it often picks up pollutants such as road sand and salt, automobile fluids, pet wastes, grass clippings and fertilizers.
Why is Stormwater Runoff a problem?
Stormwater runoff is a common source of pollution in streams, lakes and rivers. Stormwater runoff is of particular concern in urban areas. Large expanses of surfaces impervious to water, such as roofs and parking lots, make it difficult for precipitation to soak into the ground. As stormwater moves over the land and towards streams, rivers and lakes, it can be contaminated with a number of substances, such as:
· Sediment from construction sites, eroding road-banks and stream-banks.
· Organic materials, such as leaves, grass clippings and other yard wastes. When these substances are washed into streams and lakes, they decay - using oxygen in the process. This can use oxygen needed by fish and other aquatic organisms.
· Oil and gasoline leaked from automobiles and storage tanks.
· Nutrients, such as phosphates and nitrates. Often these can be traced to fertilizers washed off lawns and from failing septic systems. When nutrients enter water, they can stimulate the growth of unwanted aquatic weeds and algae.
· Pesticides, from lawns and gardens.
· Pathogens, such as bacteria and viruses, which can cause disease. These may come from improperly disposed human and animal wastes and failing septic systems.
· Other toxic substances, such as copper or lead. These may come from spilled or improperly disposed paint, or be deposited back on the land from automobile emissions.
· Trash and street garbage, such as plastics, paper and other litter.
Besides causing pollution problems, stormwater runoff also contributes to and aggravates flooding problems. The less precipitation that soaks into the soil, the more there is to run into the streams. When to much water enters a stream all at once, flooding results.
Why and how to manage Stormwater?
Traditionally, stormwater from developing areas has been handled by getting it off-site as quickly as possible. As water moves off-site, it picks up and carries with it pollutants, such as sediment, litter, automobile fluids, etc., to streams, rivers and lakes. The sheer volume of water rushing off paved or built-up areas also frequently results in flooding. Water pollution and flooding can be very costly to communities. Proper stormwater management can prevent pollution, reduce flooding, and improve a community's appearance.
The goal of any stormwater management program is to ensure that the quantity and quality of stormwater runoff from a specific development is not substantially altered from pre-development conditions.
On a specific site, such as a sub-division or shopping plaza, this means controlling stormwater where it falls on the land, using structural and vegetative measures to detain and store water. When stormwater is detained on-site, pollutants can settle or be filtered out by the soil. Peak flows are diminished, and flood damages are reduced.
Ideally, stormwater control measures are applied throughout a watershed or lake basin. This improves groundwater recharge, reduces streambank scouring and bank erosion and keeps potential contamination on land and out of streams, rivers and lakes.