Putting the Brakes on Stormwater Runoff

Federal climate data confirm what we’ve all seen in our rain gauges in recent years: extreme precipitation events are happening more frequently in Virginia. As heavy rainfalls trend upward, so does stormwater runoff and the pollution it carries into our local watersheds.

If unchecked, the stormwater flowing off roofs and driveways picks up contaminants such as fertilizers, pesticides, auto fluids and animal waste and takes them down storm drains or into nearby streams. The volume of stormwater is also damaging; intense runoff erodes soils, scours out aquatic habitat and increases sediment pollution.

The Piedmont Master Gardeners promote stormwater control methods that can enhance our home landscapes while protecting our waterways. Indeed, this was one of the themes of a Garden Basics workshop on water-wise gardening we offered last fall.

Here in Charlottesville and Albemarle County, most of our local watersheds feed the Rivanna River, which in turn feeds the James River and ultimately the Chesapeake Bay. This means that polluted runoff from our area contributes to problems afflicting the Bay, including excess nutrients (i.e. nitrogen and phosphorous) that cause algal blooms and oxygen-starved dead zones.

Every household has a role to play in addressing this issue. According to Virginia Cooperative Extension, a typical homesite with 2,350 square feet of roof and pavement will send 62,552 gallons of runoff into the surrounding watershed each year. That’s enough water to fill seven tractor-trailer tankers. VCE offers a range of practical and affordable strategies for collecting stormwater or slowing it down so that more of it seeps into the ground and less of it leaves our properties.

These include:

  • Redirection: This helps manage stormwater from the largest impervious surface on most homes: the roof. Flexible fittings and extension pipes attached to gutter downspouts direct rainwater away from the house and driveway and toward places where it can infiltrate the soil, such as flowerbeds, a vegetable garden, or a healthy lawn. Be careful not to direct rainwater to places in your yard with poor drainage and avoid soil erosion by adding devices to the extension pipes that spread the water or slow it down. If you are directing stormwater into your lawn, VCE recommends aerating it every three years to promote infiltration.
  • Rain Barrels: When attached to gutter downspouts, rain barrels reduce stormwater runoff while capturing water you can use later to irrigate your lawn and garden. A rain barrel is typically equipped with a spigot at the bottom and an opening near the top to release overflow, which can be directed either into another rain barrel or into places in the yard where it will seep into the ground. In a one-inch rain event, a thousand-square-foot roof will shed roughly 12 barrelsful of water, so be prepared to handle the excess.
  • Permeable Pavement: Rather than shedding runoff, permeable pavement allows stormwater to seep into a space below the surface, where it can be drained away safely or allowed to infiltrate the soil. Permeable pavements are typically structured in layers, including a pervious surface layer, an underlying reservoir layer, and a filter layer. The permeable surface layer can be porous asphalt or concrete, a plastic or concrete grid filled with soil or gravel, or interlocking pavers that allow infiltration. VCE suggests consulting a professional to design and install permeable pavement systems, which require ongoing maintenance to ensure that water continues to seep through.
  • Grass Swales: Unlike a simple ditch, a wide, shallow grass swale moves water along a slow path, giving it time to seep into the ground or evaporate. Swales require a gentle grade and may not be the right solution on properties with heavy clay soil. A perc test may be necessary to determine if the infiltration rate is sufficient. When establishing a swale along a property line, be mindful of any setback, right-of-way, or easement restrictions. And before you dig, consult va811.com (a.k.a Miss Utility of Virginia) to locate underground utilities. Grass swales should be at least 10 feet from building foundations, 50 feet from septic fields and 100 feet from wells.
  • Rain Gardens: A rain garden is a shallow depression that holds runoff for just a few days, allowing it to evaporate, infiltrate the ground or be taken up by plants. At times it will be very wet, and at other times it will be very dry, so it’s important to select plants that tolerate this range of conditions and to place them appropriately. For instance, plants that can stand wet feet should be in the lowest areas. Rain gardens are an ideal setting for native plants, which provide food and habitat for wildlife and help preserve biodiversity. Albemarle County’s native plant database will help you identify species suitable for rain gardens in our area, as will Piedmont Native Plants: A Guide for Landscapers and Gardens, published by the Plant Northern Piedmont Natives partnership. It lists some 20 grasses, ferns, shrubs, and other native plants that perform well in the alternatingly wet and dry conditions of a rain garden.
  • Buffers: For a property that borders a pond or a stream, a vegetated buffer will protect water quality by slowing runoff, filtering out pollutants and stabilizing the shoreline. Comprising a mix of perennials, grasses, shrubs and trees, a buffer is relatively inexpensive to establish and easy to maintain. In addition to water protection, a vegetated buffer provides an array of other environmental and aesthetic benefits, including support for wildlife. This is especially true if the border is planted with native species appropriate to the site.

These measures are even more effective when combined with one another. For example, a rooftop redirection system can channel stormwater into a rain garden, a grass swale, a buffer or all of the above. Better yet, add trees. Researchers have found that a mature deciduous tree can intercept up to 700 gallons of rainwater per year; an evergreen can catch more than 4,000 gallons annually. Such management tools help to keep polluted runoff out of our waterways while adding beauty and ecological richness to our landscapes.

References

“Virginia State Climate Summary,” Kunkel, Kenneth E. & Runkle, Jennifer., NOAA Technical Report NESDIS 149-VA, 4pp., 2017.

“The Issue,” US EPA, Nutrient Pollution, Learn.

“Decreasing Runoff and Increasing Stormwater Infiltration,” John Freeborn, Virginia Cooperative Extension, Publication 426-046, 2015.

“Rooftop Redirection (Disconnection),” Laurie J. Fox et al., Virginia Cooperative Extension, Publication SPES-9P, Stormwater Management for Homeowners Fact Sheet 1, 2018.

“Rain Barrels,” Laurie J. Fox et al., Virginia Cooperative Extension, Publication SPES-10P, Stormwater Management for Homeowners Fact Sheet 2, 2018.

“Permeable Pavement,” Laurie J. Fox et al., Virginia Cooperative Extension, Publication SPES-11P, Stormwater Management for Homeowners Fact Sheet 3, 2018.

“Grass Swales,” Laurie J. Fox et al., Virginia Cooperative Extension, Publication SPES-12P, Stormwater Management for Homeowners Fact Sheet 4, 2018.

“Rain Gardens,” Laurie J. Fox et al., Virginia Cooperative Extension, Publication SPES-13P, Stormwater Management for Homeowners Fact Sheet 5, 2018.

“Effects on Water Quality,” Johnson, James E. & Klapproth, Julia C., Virginia Cooperative Extension, Publication 420-151, Understanding the Science Behind Riparian Forest Buffers, 2009.

“Part 1: Methods for Increasing Forest Cover in a Watershed,” Karen Cappiella et al., Center for Water Protection, published by USDA Forest Service, July 2005.