Shelter: Rain Gardens May Save the Sound

Avoiding a flooded basement--and saving Puget Sound--could be as simple as putting in a rain garden
Lyn Dillman

Category: teaser headlines


Avoiding a flooded basement--and saving Puget Sound--could be as simple as putting in a rain garden

The rain gushing from downspouts this time of year can seem like water torture for local residents, as it puddles on lawns, spills over sidewalks and seeps into basements. Home-owners seek relief in the form of drainage systems, permeable driveways or even green roofs. But there’s another panacea that’s likely more cost-effective than all the others: a rain garden. Proof that it works? The City of Seattle, after installing test gardens, found this hydrophilic landscaping feature so effective that it will roll out rebates in March for some homeowners willing to dig in to this environmentally friendly practice.

“As an effective way to address storm water on a private parcel basis, a rain garden is probably one of the easiest things you can do that makes a difference and that gives you a benefit as a homeowner,” says Bob Spencer, RainWise program manager at Seattle Public Utilities. According to Spencer, a substantial amount of a home’s roof runoff can be contained and filtered in a properly sized and sited rain garden.

The basic design requires a depression in the ground about 6 to 12 inches deep. This can be a kidney, saucer, trench or other shape, but to adequately handle runoff it will need to be proportional to the surface area of your roof—plug your address into the RainWise Web site (, and it will do the math for you. (If a roof is 1,000 square feet, according to the RainWise formula, the base of the rain garden will need to be about 75 square feet.) The sunken garden should be compost-rich, to absorb water like a sponge, with the bottom thickly planted with water-tolerant species. Native plants, such as Northwest species of dogwoods, ferns, red-flowering currants and Douglas irises, are recommended. Water can be directed from the house to the garden directly across the lawn (taking advantage of a gradual slope), through a trench filled with rocks or through an underground pipe. Spencer says a do-it-yourself job can cost as little as $500. (Hiring a contractor and choosing pricey plants could, of course, stretch that number into the thousands.)

Though it would be nice to stop worrying about a flooded basement, the main reason for the city—and you—to grab a shovel is less self-serving: It’s a great way to improve water quality in Puget Sound and urban streams. In many older Seattle houses, antiquated sewage systems combine a household’s wastewater and storm water in one pipe, often sending both to a city wastewater treatment plant. A serious winter storm can overwhelm the wastewater system and release untreated water into Puget Sound—an event called a combined sewer overflow, or CSO. Every home that collects its own runoff lowers the chance of a CSO. It also reduces the amount of water blasting into urban creeks, which is a benefit to struggling salmon populations. Additionally, the rich soils and leafy plants of a rain garden act like a backyard Brita, filtering pollutants from the water before it re-enters the water table.

Unlike some eco-measures (scratchy recycled toilet paper; unattractive compact fluorescents), this particular innovation is also less hair shirt than enhancement. Lyn Dillman, whose West Seattle rain garden was designed by In Harmony Sustainable Landscapes in 2008, had a patio installed next to her rain garden. “It’s a nice oasis,” she says. Instead of relying on a downspout to funnel her roof runoff, Dillman hung a copper rain chain that feeds into a small catch basin. This connects underground to flexible piping that leads to the garden. “It’s all covered with river rock, so it looks like I have a little streambed through my yard,” she says.