SPU releases draft map of Ballard Drainage Project rain gardens

Seattle Public Utilities recently released a map featuring the proposed locations for the Ballard Natural Drainage Project rain gardens in the neighborhood.

The map was released at the end of February after an Open House event was held to gain feedback on the proposed rain garden types and their locations.

The Ballard Natural Drainage project has been in the works since 2012 in an effort to keep polluted runoff out of the sewers (and our waterways) with a system of roadside rain gardens.

Without a natural drainage system, heavy rain can cause polluted runoff and sewage to overflow into lakes, streams and the Puget Sound. Due to the runoff’s impact on our water quality, and because of the federal Clean Water and state regulations, SPU are taking measures to reduce the overflows in our neighborhood.

As a neighborhood, Ballard represents a third of all combined sewer overflows from Seattle’s system. According to SPU, during the high rain year of 2012 the sewers in Ballard deposited 54 million gallons of raw sewage and polluted rainwater into Portage Bay out of the 154 million gallons deposited by all of SPU’s other systems combined. Although 2013 brought less rainfall, Ballard still contributed to one-third of all flows.

SPU is currently in the draft planning stages of constructing the natural drainage project in planting strips along 17 blocks in Loyal Heights. Check out the list of the specific rain garden locations as shown on the current draft map:

  • 17th Ave NW – between NW 77th and NW 83rd Streets.
  • 19th Ave NW – between NW75th and NW 77th Streets.
  • 26th Ave NW – between NW 80th and NW 83rd Streets.
  • NW 75th St – between Jones Ave NW and 17th Ave NW.
  • NW 77th St – between 17th and 19th Avenues NW and between 25th and 26th Avenues NW.

Throughout the planning and construction period, SPU will coordinate with the Neighborhood Greenways program (which is planning the greenway on 17th Ave NW) and with SDOT’s Safe Routes to Schools program.

The areas chosen for the rain gardens were determined by a series of test borings that sought well-draining soils (called glacial outwash or glacial recessional soils). Ultimately, SPU’s decision about the final rain garden locations will rest on multiple factors including the volume of stormwater that can be managed, potential impact to existing trees, existing soil conditions, location of existing utilities and community input.

Two types of rain gardens, including the side slope and bulb-out options (pictured below), are set to be installed with the garden type depending on the specific location. Each rain garden will also feature different plants that, according to SPU, will be both visually pleasing and environmentally beneficial.

Side slope cross

bulb cross

Locals have expressed concerns about how both the construction and the presence of rain gardens themselves will impact their daily lives. One major concern is the possibility of basements flooding in the area. According to SPU, the Natural Drainage Project will be designed to allow stormwater to slowly seep into the ground and away from basements, usually at depths lower than most basements.

“SPU does not know of any rain garden projects that have caused increased basement moisture,” writes SPU on their website.

In terms of parking and construction, SPU confirms that Natural Drainage Project impact will be as minimal as possible. No legal on-street parking will be affected by the project and new curb bulb-outs at certain corners will prevent illegal parking.

When construction begins, locals can expect to see construction crews working in the area directly in front of their home for between one and two months. Specific impacts in front of any single home is set to be intermittent as construction progresses. The most significant impacts, which include excavation and sidewalk work, will each last about one to three weeks at a time, with excavation occurring earliest in the project, and then sidewalk installation at the end.

The project team will continue refining the designs throughout the spring and summer with construction anticipated to begin in late summer this year.

Click here to check out more information on the Ballard Natural Drainage Project website.

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