Rain gardens, center medians to help with drainage in Oakbrook

“I have been ranting about this idea of dumping street drainage into pristine Peterson Creek, which flows into Burnt Bridge Creek,” Keim said. “These are all microcosms of bigger problems, contributors as to why our environment is in bad shape. Even though it doesn’t seem like much, they all add up.”

The current drainage system is storm drains on 98th Avenue. The grate filters only large debris, not silt or pollutants. One drain is just steps from Keim’s front yard and Peterson Channel.

Thanks to a $600,000 Low Impact Development Grant from the Washington Department of Ecology, future stormwater flowing into Peterson Channel will be clearer.

Keim said he’s looking forward to having a front-row seat to the construction of 15 rain gardens and center-lane medians along about a half-mile stretch of 98th Avenue, from Burton Road north to Northeast 34th Street. The city received the grant and is managing the project.

“This is one of the larger, grant-funded projects for a rain garden,” said Annette Griffy, the city’s surface water manager. “It’s one of the first integrated into the street.”

Keim is one the Oakbrook neighbors who have met with Griffy and other city staffers to help develop design plans for the project. The city expects to receive build bids soon. Construction, expected to begin in mid- to late April, should last about 45 days.

Filtering stormwater

Each rain garden will be about the width of a car and about two car-lengths, Griffy said.

They will capture stormwater runoff with a combination of native plants, compost and a bioretention layer, consisting of a specific mix of sand and compost, said Daniel S. Gariépy, a stormwater engineer with the Washington State Department of Ecology. The rain gardens will allow stormwater drainage to seep into the ground, instead of flowing directly into Peterson Channel.

“That’s more like it used to be, more like nature intended it,” said Gariépy. “These pollutant-removing facilities clean over 90 percent of the volume of water runoff. The plant roots capture some of the problems found in stormwater runoff, such as suspended solids,” he said.

Rain gardens, which have been part of the urban landscape for more than 20 years, can restore the surface flow to what it was before there were large swaths of impermeable roads, driveways and roofs, he said.

After 20 years of use “they are still capturing pollutants including suspended solids, like when you see mucky water,” Gariépy said.

A retired engineer, Oakbrook neighbor Keim understands the benefits of rain gardens. He’s looking forward to seeing clearer water flow in Peterson Channel.