Rain Gardens

A natural landscape feature that helps to manage runoff
and keep our water clean.

A rain garden is a simple, beautiful and functional way to improve the landscape and improve local water quality.

Up to 70% of the pollution in our surface waters comes from stormwater. Rainfall runs off roofs, roads and lawns, washing away accumulations of sediment and other pollutants such as fertilizers, pesticides and motor oil, which are then carried to the nearest stream.

A rain garden is constructed on a low spot below a grass-covered area over which stormwater run-off tends to flow. It can hold water for up to 48 hours, giving it a chance to seep naturally into the ground. Water that is captured by a raingarden is filtered by mulch and soil, taken up by plants, cleaned of many pollutants and is added to the groundwater supply.

How do you build a rain garden?
For a small residential "backyard" type of installation.

Step #1: Dig a Hole
Dig an area 3-4 feet deep. The surface area of a rain garden (in square feet) depends on the size of the area that contributes runoff to the garden (the drainage area). The surface area of a rain garden should be roughly 7% the size of the drainage area (multiply the size of the drainage area by 0.07).

Step #2: Add a Layer of Sand
Fill the bottom of the hole with a layer of sand one foot deep at the bottom. This reservoir will hold water long enough to slowly percolate into the ground.

Step #3: Fill with good Organic Soil
Fill the rest of the garden with good gardening soil consisting of a mix of top soil, sand and leaf compost. The surface of the of the rain garden should be about 6 inches below the surface of the surrounding ground so that water can collect there.

Step #4: Add some Native Plants
Plant attractive native groundcover, shrubs and trees which thrive on excess nutrients that are harmful to surface waters, and provide habitat for local wildlife.

Step #5: Cover with a layer of mulch
Covering the garden with four to six inches of mulch absorbs water and keeps it moist during dry periods.

How does a rain garden handle runoff?

Filtration
Mulch, organic soil and sand filter out particles of pollution as stormwater percolates through the layers of a raingarden.

Nutrient Uptake
The nutrients found in fertilizers and pet waste are a major source of pollution in local waters and in the Chesapeake Bay. The plants in the rain garden remove nutrients from water.

Pollutant Breakdown
Bacteria and Fungi found in mulch and soil have the ability to break down many pollutants including the hydrocarbons in oil and gas.

Groundwater Recharge
The water that is processed by a rain garden gradually percolates into the surrounding soil and has the opportunity to infiltrate through layers of soil down to the water table below. Recharging the groundwater provides water for wells and surface water such as ponds and streams.

For photos of the RSEP workshop on rain gardens, documenting the installation of a rain garden, click here.
Check the Albemarle County Native Plant Database for recommended Rain Garden plants. 
To see a printable brochure on rain gardens, click here.

For more information about rain gardens and stormwater management, check out the following web sites:

City of Charlottesville

Department of Forestry

North Carolina