When winter storms caused basements to flood and sewer lines to back up for many North Everett residents in 2010, the city stepped in to help. It collaborated with WSU Extension and the Snohomish Conservation District to design and build seven rain gardens — a low-impact solution for drainage problems. In exchange, the homeowners signed a contract with the city to maintain the gardens for five years.
In addition to adding beauty to the yards on Lombard Street, the rain gardens have removed 123,000 gallons of stormwater from the combined sewer system each year since they were installed.
“Many of the homes in North Everett were built with a trough around the basement,” said Marla Carter from City of Everett Public Works. “Now the owners are reporting that their basements are dry. They haven’t been in years, so we know the project has been effective.”
Everett was recently acknowledged for its Rain Garden project by Puget Sound Partnership as one of several “Puget Sound Champions.”
“Storm water is the number-one polluter of Puget Sound,” said Curt Moulton, director of WSU Snohomish County Extension. “When people invest in rain gardens for their own homes, it is a way for them to reduce the pollution in Puget Sound.”
Washington State University and Stewardship Partners are leading a campaign to install 12,000 rain gardens in the region by 2016. According to their website, rain gardens work like a native forest by capturing and infiltrating polluted runoff from rooftops, driveways and other hard surfaces. If the goal is met, the rain gardens will soak up 160 million gallons of polluted runoff, which will protect local waterways, significantly helping to stop the storm water crisis in the region.
“The alternative is a treatment plant,” Moulton said. “Rain gardens have a much lower impact and allow everybody to take responsibility for the storm water from their property [instead of paying more taxes].”
Making a rain garden
Although the steps to making a rain garden are fairly straightforward, there are a lot of details to the process, according to Moulton. Here are the basics:
Choose the location. Determine the area in your yard that needs drainage and where the water from your roof drains to identify the best location for a rain garden. Make sure to place the garden at least 10 feet from the house, on fairly level ground, and away from utilities.
Do a perk test. Dig a 24-inch fence post hole in the potential location (when the ground is moist) and fill it with water. The water must disappear “at a decent rate” (specifics can be found in the Rain Garden Handbook by WSU Extension). If it doesn’t absorb into the ground, either choose another location or amend the soil until it does. To amend the soil, mix it with compost. If the soil is clay-like, add sand as well as compost. For advice about perk testing and unique problems associated with soil drainage, call the Conservation District in Snohomish County at (425) 335-5634.
Design and build. Once you have determined the size and shape of the rain garden, excavate 18 to 30 inches of soil, and level the bottom of the garden without compacting the soil. Place the amended soil mix into the garden, leaving at least six inches below the edge of the garden, and level the surface. Then install a swale, pipe or landscaping for water to enter the garden and make a rock-lined overflow area.
Plant. There are three zones in a rain garden, and each requires a different type of plant. The bottom zone, where water may pool up to six inches and then gradually drain, must have plants that can tolerate saturation. Above that, the transitional zone is sloped and should have plants that can tolerate some moisture but not saturation. And the upper zone, or berm, around the garden can be planted with the same foliage and flowers that are in the rest of the yard. Call the Master Gardener Hotline at (425) 357-6010 for help with plant choices.
Maintain. Mulch as needed to prevent erosion and weeds in the rain garden, keep the inlet and outlet clear of debris and well protected with rocks, water the plants as needed, and do not use fertilizer or pesticides.
To download a copy of the Rain Garden Handbook for Western Washington Homeowners, go to http://raingarden.wsu.edu.