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Environment | Communities

Neighbors Fight Stormwater Pollution by Building Rain Gardens

SEATTLE —- Three months ago, Karrie Kohlhaas didn’t know what a rain garden was. Now she has one in her front yard and there are nine others on her block.

That’s how fast rain gardens are spreading around the Seattle metropolitan area.

The gardens are part of a campaign by Washington State University and the non-profit Stewardship Partners. Their goal is to install 12,000 rain gardens in Puget Sound communities by 2016. So far, more than 700 gardens have been installed (see a map of them) and more are being added every week.

“Twelve thousand gardens will absorb approximately 160 million gallons of stormwater each year,” said Stacey Gianas, who is with Stewardship Partners.

That much water would fill 250 Olympic swimming pools. And its stormwater, which washes over roofs and streets, picking up all kinds of pollution. Usually that contaminant-filled water runs into storm drains that empty into waterways and rivers.

One goal of the campaign is to strategically build clusters of gardens in neighborhoods near streams and marine shorelines that are known to suffer from substantial stormwater runoff.

For instance, Longfellow Creek, which cuts through the North Delridge neighborhood, is so polluted by stormwater runoff that 88 percent of Coho salmon that return to this urban stream die before they can spawn, according to a 2003 King County Stormwater Services report.

Karrie Kohlaas, who lives in North Delridge, discovered rain gardens in an email.

“I didn’t know what a rain garden was,” Kohlhaas said. “But I thought it sounded interesting so I just stopped what I was doing and picked up the phone and called Stacey.”

Kohlhaas and Gianas met the next day and took a walk down Kohlhaas’ street, 25th Avenue Southwest, and started talking to neighbors about rain gardens.

How well do rain gardens work?

The new Washington Stormwater Center is doing the research. Read more about it.

Gianas explained that rain gardens look similar to most gardens, except they’re neither raised nor flat. They’re built in a shallow depression, like the shape of a bowl. Rain gardens take in stormwater runoff from impervious surfaces like roofs, driveways, walkways and parking lots. Once the water reaches the rain garden, a mixture of soils absorb the water and strain it like a sieve, filtering out sediment, heavy metals, oil, grease and other pollutants.

“Rain gardens mimic a forest because they’re built to have layers of vegetation and thick spongy soils,” Gianas said. “There’s not room to put a forest back into the urban area, but rain gardens are like mini forests and the more rain gardens we build, the more of an impact they can make.”

Rain gardens are not meant to hold water like a pond or a wetland, Gianas explained. A properly functioning rain garden will hold water for no more than a couple days after a storm.

During her visit to North Delridge, Gianas conducted a soil drainage test, also called a “perc test,” which is the first, and possibly most important, step in building a rain garden.

Gianas found that the neighborhood had well-drained soils, so she applied for a Community Salmon Fund grant through the National Fish and Wildlife Foundation on behalf of the neighbors to pay for the gardens. The hope is that this cluster of rain gardens will serve as a model for other residents in the area, Gianas said.

Build your own rain garden

For more details on how exactly to build a rain garden, watch this

or download this handbook on building rain gardens from Washington State University

Within four days, 10 North Delridge neighbors had committed to building rain gardens in their front yards, and David Hymel and his team at Rain Dog Designs were there to help them. Hymel’s team surveyed the yards and custom-designed each garden to suit the location and the homeowner.

“For every 1,000 square feet of roof, you need 100 square feet of rain garden,” Hymel told North Delridge residents as he showed them how to disconnect a downspout to divert roof water into a rain garden.

“I’m worried about water coming back into the basement,” Kohlhaas said. “How often have you seen rain gardens not work?”

“Zero,” Hymel said.

But rain gardens can fail if they’re not properly installed. Last year problems arose with rain gardens in the Ballard neighborhood. The gardens filled with water during the winter and didn’t drain. Neighbors started a blog calling for the removal of the gardens. The whole episode has been much publicized, and the City of Seattle is in the process of removing them, at an estimated cost of $500,000.

Hymel assured the residents in North Delridge that the Ballard rain garden fiasco was an anomaly and that his team has built 140 rain gardens throughout the Puget Sound region and all are functioning properly.

Share your stories

What is your experience with rain gardens? Have you installed a rain garden or know someone who has? Share your photos, thoughts and stories below or send a video response on YouTube.

A few weeks later, Hymel’s team had prepared 10 rain garden sites for the residents on 25th Avenue Southwest. They gathered with volunteers on a Saturday in August and filled their new gardens with plants and mulch.

Kohlhaas’ eyes welled up with tears as she watched her neighbors digging in each other’s yards. Planting these rain garden, she explained, had the unexpected effect of bringing the community together and uniting her neighbors in a common purpose.

“This rain garden project has been a positive all around,” Kohlhaas said. “It beautifies our block. It adds value to our homes. And it has an environmental impact that’s positive. I hope it spreads, not only in our neighborhood, but around Puget Sound and around the state.”

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