Landscaping for water quality
Even the name sounds tranquil: “rain gardens.” It conjures up images of peaceful places of beauty — lush, green, and shimmering with water from a passing shower.
The label can be deceiving, however. Yes, rain gardens are lovely — but they are also extremely useful tools in the effort to slow runoff and filter pollutants from storm water.
A rain garden, in its simplest form, is a shallow depression in the ground that’s filled with permeable soil and landscaped with hardy flowers, grasses, shrubs, or trees. The area fills with a few inches of water when it rains, then allows the water to slowly soak into the ground rather than running off to storm drains. In the process, pollutants such as motor oils from your driveway and fertilizers from your lawn are broken down by microorganisms in the soil and absorbed by vegetation.
The result? An attractive landscape feature that helps to improve the water quality of your nearest stream, river, or reservoir.
According to TVA’s Shannon O’Quinn, the key is to site your rain garden properly and pick the right plants to install in it. “If you do that, nature will take over and you’ll have an easy-to-maintain, eye-catching addition to your property with the potential to attract butterflies, birds, and wildlife.”
O’Quinn, a member of TVA’s Holston-Cherokee-Douglas Watershed Team, offers this advice on siting and plant selection: “Choose a location at least 10 feet from the foundation of your house, preferably in a flatter part of your yard with full or partial sun. Use native plant varieties that are well-suited to your area. Good choices for the Tennessee Valley include winterberry, white fringe tree, black chokeberry, cardinal flower, red osier dogwood, Virginia wild rye, bleeding heart, wild columbine, Virginia sweetspire, and goldenrod.”
It’s important to note that rain gardens differ from wetlands — areas where wet soil is the rule, rather than the exception. “Rain gardens can survive short periods of standing water,” says O’Quinn, “but correctly designed rain gardens should drain within a day or so after rainfall stops.” For this to happen, the rain garden must be correctly sized for the drainage area and must have well-drained soils. An under-drain can be used if the soil doesn’t drain freely; this guarantees that the storm water will filter through the soil without too much ponding.
O’Quinn and his colleagues have been involved in several rain garden installations. He is convinced the concept has wide applicability and can have great benefits for property owners. “Homeowners can build small rain gardens at each gutter downspout to collect runoff from their roofs or pick a low spot in their yards where the water naturally drains to collect rain water from their driveway or lawn. Developers can install larger rain gardens to handle storm water from commercial parking areas or entire subdivisions.
Rain gardens can be viewed as one item on a menu of urban best-management practices, says O’Quinn. “Depending on site characteristics, rain gardens can have distinct advantages — both aesthetically and environmentally — over more typical storm-water management practices such as detention ponds. And since much of the pollution in our streams, rivers, and reservoirs is carried there by storm water, anything we can do to minimize that will have benefits to the environment.
“People think of pollution as something that comes from a factory or sewage treatment plant, dumping directly into a river. But a lot of harmful substances entering our waters come from our roofs, driveways, yards, and parking lots. A single rain garden may seem insignificant, but collectively rain gardens could produce substantial environmental benefits.”
O’Quinn hopes shoreline property owners will consider incorporating a rain garden into their landscaping plans. “It can be your personal contribution to cleaner water, healthier fish and wildlife populations, and a better environment for your family and community.”
You can find a wealth of information about rain gardens online, or contact Shannon O’Quinn at 423-467-3807.