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Rain Gardens: A greener approach to landscaping

As spring has sprung, you probably have noticed homeowners sprucing up their yards with flowers and shrubs, lawns being mowed, and people spending more time enjoying the outdoors.  It may bring a wonderful sense of contentment and satisfaction to feel the sun on your face and watch birds flitter in and out of the trees. However, with spring comes showers and storms. Have you noticed what may be happening in your yard during and after a rain storm?

This past spring has already brought us a lot of rain. I have noticed that at times my gutters are overwhelmed by the volume of water and overflow. What happens to all of that water? In many cases, gutters empty along driveways or across short stretches of lawn where water eventually finds its way into the closest storm drain. Heavy rain events do not allow for water to soak into the ground before flowing into a nearby storm drain.

Rain water quickly flows across the surface of the ground and along pathways and driving surfaces. Often times, stormwater may pick up and carry with it sediment, nutrients from lawns, waste from farms and pets, oil and litter from streets, and many more contaminants before flowing into streams or entering storm drains to be transported directly into the nearest local waterway.

Stormwater is a major source of pollution that affects the entire Chesapeake watershed, from the far-reaching headwaters of Pennsylvania and New York down to the main-stem Chesapeake itself. This ubiquitous problem poses a great challenge to the restoration of the Chesapeake as pollution may enter waterways a number of ways and crosses all walks of life. However, as such, all citizens within the Chesapeake watershed can help make positive changes in the reduction of stormwater runoff… and they can start right in their own backyards.

Rain Gardens

One effective tool that we can use to help reduce stormwater runoff is the installation of rain gardens. Rain gardens are gardens landscaped with native plants that are indigenous to the Chesapeake Bay region to collect, store and infiltrate stormwater runoff in its loose amended soil and strategically placed to intercept stormwater runoff until it can be fully absorbed into the ground. Their design allows the rain garden to serve almost as a bowl that collects water from downspouts or from sheet flow across a property. The water is then able to slowly infiltrate into the underlying soil. The existing soil within the rain garden is removed (or amended) and replaced with a more permeable soil that allows for easier water penetration. Sizing of rain gardens is dependent upon the amount of water that is expected to enter it during a rain event. The rain garden is planted with shrubs and perennials and mulched. The completed rain garden will have a slight depression, but will have the same look and feel as any other landscaped bed, but with the added benefit of increased stormwater infiltration. Larger and more sophisticated rain gardens that include an underdrain may also be installed to handle large volumes of water on commercial sites or similar properties.

Native Plants

Native plant (or BayScape) gardens use native plants that are indigenous to the Chesapeake Bay region. Native plants typically require less maintenance than other plants found at local nurseries or hardware stores. Once native plants are established, they require little or no water, fertilizer, and pesticides and may provide wildlife habitat and attract pollinators such as butterflies, hummingbirds, and bees. Native plants can be used to stabilize steep slopes and decrease lawn area that must be mowed. Lawn mowing produces up to 5% of the nation’s air pollution, with one new gas powered lawn mower producing more air pollution in one hour of operation as 11 new cars each being driven for one hour, according to the U.S. Environmental Protection Agency (EPA). Another benefit of reducing lawn area is the reduced amount of fertilizer and other chemicals treatments on many residential properties. The following link is a good source for choosing native plant material: http://www.nps.gov/plants/pubs/chesapeake/pdf/chesapeakenatives.pdf

Request more native plant stock at your local nurseries. Currently, most plant nurseries and garden centers carry only approximately 10% native plants in stock. Ask your local landscapers about rain gardens and encourage them to complete a training course. The Alliance offers rain garden trainings for local landscape contractors as part of our RiverSmart Homes program.

Alternatives To Rain Gardens

Rain barrels are also an excellent way to capture rainwater from rooftops to allow for slow release into the ground or even for use in watering gardens or washing cars, preventing rapid flow across the ground and into storm drains that often overwhelms the stormwater system.If your property is not suitable for a rain garden, consider installing a rain barrel or directing your downspouts into landscaped areas.Small steps to diffuse and slow down rainwater before it can enter a storm drain can have a significant impact on water quality of local streams and rivers.   Imagine the benefits if everyone redirected the water flow from one of their downspouts.

Tips for rain garden installations

If you think your property may benefit by installing a rain garden, you may want to consult a professional, but please consider the following recommendations:

  • Place the rain garden a minimum of 10 feet away from any existing foundation or retaining wall. This will prevent water from finding its way into your basement or undermining retaining walls.
  • Rain gardens should be placed in areas with a 2-10% slope to allow adequate collection of water within the rain garden.
  • Conduct a percolation test of your soil. Water needs to be able to infiltrate into the ground. If your soil is mostly clay, this location may not be suitable for a rain garden. Water should be absorbed into the ground within 24 hours of a rain event.
  • Rain garden depth should be a minimum of 18-24”. Existing soil should be completely removed and replaced with a bioretention soil mix. The bioretention soil mix ratio should be 65% concrete sand, 20% topsoil, 15% compost/leaf mulch. There should be no more than 10% clay. Existing soil may also be amended to the above specifications.
  • Excavated soil should be used in berm construction. The berm must be compact and level to provide sheet overflow.
  • If a downspout is piped to the rain garden, then the pipe should be at least a 2% grade down and away from the house. Any pipe used that is past 10 feet from the foundation of the house should be perforated. Preferably, piping should be rigid to prevent from being crushed or otherwise damaged. If the rain garden design incorporates a downspout extension, the extension pipe may be buried and should terminate at the upper rim of the rain garden (rather than nearer to the bottom).
  • If a downspout drains to the rain garden, there should be river rock or similar material at its outlet to prevent strong gushes of rain water from eroding the mulch and soil in this area and washing out the rain garden.
  • Apply approximately a 2-3″ hardwood mulch layer to your completed rain garden.
  • Native plants to the Chesapeake Bay region are recommended.
  • Plant water tolerant plants toward the center of a rain garden. These plants will be inundated with rain water for a period of time after a rain event.
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Jamie Alberti RiverSmart Homes Senior Program Manager, DC Office

Jamie is Senior Program Manager of RiverSmart Homes, where she oversees the Alliance's rain barrel and landscaping projects in D.C. Jamie enjoys her current position with the Alliance because it allows her to combine watershed restoration with environmental education opportunities.

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