One of the best ways to prevent stormwater runoff in a home landscape is to create biofiltration gardens. Also known as rain gardens or bioswales, the gardens use plants, soils, mulch and microbes to slow and treat stormwater runoff. This management practice is modeled after natural ecosystems and has been shown to effectively reduce heavy metals, nutrients, bacteria, water temperatures and other pollutants (Prince George’s County 2007). In an ornamental garden, biofiltration areas can be easily integrated into the landscape and filled with a variety of beautiful plants. The gardens hold standing water temporarily and typically drain within 24 to 48 hours. Because water is only held for short periods of time, biofiltration gardens are typically not habitat for mosquitoes. By cleaning stormwater and encouraging infiltration, rain gardens and bioswales provide a variety of benefits including:
- Reducing stormwater runoff and the likelihood of flooding.
- Protecting local streams and lakes from pollution and physical damage caused by chemicals and debris carried by stormwater.
- Increasing the amount of water for your landscape.
- Replenishing groundwater supplies.
A rain garden is a strategically-located low area where water can soak naturally into the soil. Rain gardens can be any size or shape and are easily integrated into your overall landscape.
Bioswales are shallow vegetated channels that slowly convey and absorb rainwater runoff. They can be used to direct surface runoff to rain gardens or other areas of the landscape where the water can be absorbed. Bioswales can be woven into the garden and vegetated with a variety of trees, shrubs and perennial plants. The longitudinal slope of a bioswale typically ranges from one to six percent. Decorative rocks, check dams and vegetation can be used to control and slow the velocity of water moving through the channel. Similar to rain gardens, bioswales typically have three wetness zones. In the lowest zone, plant species should be selected that can tolerate short periods of standing water as well as fluctuating water levels and dry conditions. In the middle zone, vegetation will need to tolerate both wet and dry conditions. And in the upper zone, along the outer edges of the bioswale, plants should be suited to drier conditions.
Limit impervious surfaces
Impervious surfaces are typically constructed surfaces—rooftops, sidewalks, driveways, roads—covered by impenetrable materials such as concrete, blacktop, and mortared brick or stone. But urban and suburban soils, which are often compacted by intense foot traffic or construction equipment, can also be highly impermeable. As urbanization increases, so does the amount of impervious surface. Studies have shown that the quality of many urban watersheds is correlated to the amount of impervious cover in the watershed. Because they prevent precipitation from seeping down into the soil, impervious surfaces are a primary cause of elevated stormwater runoff. Torrents of destructive runoff are generated as rainfall strikes rooftops and pours into gutters and downspouts, picking up volume, speed, and pollutants as it rushes over paved surfaces and into storm drains.
Homeowner strategies to reduce impervious surfaces include:
- Construct two-track driveways and service roads with a center strip of vegetation or other permeable surface.
- Use stepping stones surrounded by creeping groundcovers instead of continuous impermeable pathways.
- Opt for “dry laid” instead of “wet laid” or mortared patios and walkways. Set in sand, these allow some stormwater to infiltrate into the soil, unlike the cement products typically used as mortar.
- Allow green spaces between patios, pathways and other impermeable spaces
- Restore the ability of soils to absorb rainfall and take steps to prevent soil compaction elsewhere in the landscape.
- Consider permeable paving, such as concrete products with a porous structure that allow water to pass directly through the surface.
Protect and restore vegetated buffers along waterways and wetlands
In undisturbed natural areas, waterways and wetlands are typically protected by adjacent vegetation. Grassland, woodland and wetland plant communities naturally infiltrate and cleanse stormwater. Buffers along waterways and wetlands also improve wildlife and fish habitat by providing food, shelter, and shade. When vegetation is replaced by impervious surfaces, stormwater runoff increases. Stormwater often carries pollutants such as nutrients from fertilizers, pet wastes and sediment into natural water bodies. These pollutants reduce water quality and negatively affect wildlife habitat. In residential areas, turf grass often extends all the way down to the water, polluting it with fertilizers and pesticides routinely used in lawn care.
In developed areas, vegetated buffers can fulfill the same important ecological functions as undisturbed waterside vegetation. As the name suggests, these are thickly vegetated strips of land that protect waterways and wetlands from polluted runoff and erosion. They also provide habitat for a variety of wildlife year round, including “stopover habitat” for migrating birds in spring and fall.
Research shows that as the width of a vegetated buffer increases, its environmental benefits also grow. Buffers less than 50 feet wide offer minimal protection, while those 200 to 300 feet in width improve water quality and protect aquatic habitats. Vegetated buffers more than 300 feet wide can function as wildlife corridors and even harbor imperiled and sensitive species.
How to create a vegetative buffer
- Create a thickly vegetated and undisturbed buffer at least 50 feet wide. Riparian and coastal zones are often regulated; property owners should contact local and regional government agencies for information on appropriate vegetation buffers in their area.
- Avoid using pesticides or fertilizers—even organic fertilizers including compost—in a vegetated buffer.
- Undisturbed buffers provide the best protection. If access to the water is needed, create an elevated walkway made from untreated wood to protect the vegetation as much as possible.