Rooftops, roads, decks, parking areas and driveways do not allow water to soak into the ground. So when it rains, the water runs off these hard surfaces into a storm sewer, lake, river or wetland. Often this rainwater picks up contaminants, soil particles and nutrients.
Runoff into a lake or river can reduce water clarity, damage vegetation, and harm fish and wildlife habitat. In some areas, runoff from hard surfaces can change the water temperature of the lake or river. This warmed water comes from roads and parking lots and can negatively affect aquatic plants and animals.
The best way to prevent runoff of rainwater is to have it soak into the ground near where it falls. Rain gardens are one way to capture rainwater (and snow melt) for a short time. Rain gardens are landscaped areas planted with wildflowers and other native vegetation with long roots. After a rain event, the garden fills with a few inches of water, which slowly filters into the ground, usually over a period of two to four hours. Compared to a conventional patch of lawn, a rain garden allows about 30 percent more water to soak in. Between rain events, the rain garden dries out.
In addition to absorbing water, rain gardens provide valuable habitat for birds, butterflies and many beneficial insects. Below the surface, rain gardens pull phosphorus and nitrogen out of the rainwater runoff and store it in plants and the soil.
To locate a rain garden, watch where rainwater naturally forms rivulets and where it pools in the yard. A rain garden manual for homeowners is available online at files. dnr.state.mn.us/waters/watermgmt_section/ shoreland/raingardenmanual.pdf
Capturing rainwater in rain barrels connected to downspouts from the roof is another way to prevent some runoff. The water is collected and stored for later use, usually for watering gardens or house plants.
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