SPU's original raingarden test site at 30th Avenue Northwest and Northwest 83rd Street.
Something stinks in Salmon Bay and it’s not the fish
SPU project helps divert stormwater overflow
When it rains in Ballard it dumps. When there is more than one tenth of rain, hundreds of gallons of sewage and stormwater rush into Salmon Bay from the Ballard Basin.
In 2013 Ballard accounted for over one-third of the entire city’s overflows. That year Ballard overflowed 58 times, totaling 14.9 million gallons.
“It’s a water quality issue; neither our regulators nor the public like the idea of sewage overflowing into Salmon Bay. It is not good for quality of the water or the critters that live in the water, ” wrote Shanti Cowell of SPU.
To make sure the “boom boom” does not make it into the big water, Seattle Public Utilities have taken action.
The problem is that rain overwhelms the system before it can be moved. The goal is to divert stormwater so the sewage system is unaffected by fluxes of water.
SPU has multiple ways to address the issue through their Ballard Basin project. It combines Green Stormwater Infrastructure (GSI), also known as natural drainage systems (NDS) or raingardens, and future underground storage near Salmon Bay that will filter and collect dirty water.
Rain gardens are landscaped areas that absorb influxes of stormwater. They are designed to act as natural landscapes, lush with plants and natural materials in the soil that soak up rain like a sponge and filter water. The more beds, the more filtered storm water and less pressure on the system.
Together, raingardens and storage will provide almost six million gallons of storage capacity in the basin. The project is spurred by last year’s Consent Decree, which stipulates a regulatory target of no more than 1 overflow per year.
The NDS project has two phases. It’s first phase was conducted in 2012 and consisted of constructing rain gardens along several streets in Loyal Heights.
After SPU built the beds, they tested them for overflow absorption. They found that they reduced peak flow rates by over 80 percent and reduced the amount of overflow into Salmon Bay. Then in 2013 preferred blocks were identified after public outreach and initial investigations that analyzed infrastructure and soil composition.
The second phase is underway. SPU is currently designing 22 additional blocks in the Loyal Heights/North Ballard Neighborhood. They are looking for areas along sidewalks that do not have infrastructure and can easily be made into raingardens. SPU plans for plenty of public input.
“We will continue looking into underground utilities and soil conditions at the preferred raingarden locations and gather input about the design, including specific locations along the project block, access points to homes, preferences for plant concepts, and other design issues. Periodic updates will be sent to interested parties and block-by-block outreach will continue in the project area,” SPU wrote in a statement.
The proposed project covers 22 blocks. Because there are longer and shorter blocks SPU considers one block to be approximately 330 feet long.
Proposed areas are along 25th and 26th Avenue Northwest from Northwest 77th Street to Northwest 83rd Streets; 24th Avenue Northwest to 20th Avenue Northwest on Northwest 75th Street; and 17th Avenue Northwest from 77th Street to 83rd Street Northwest.
SPU met with the Ballard News-Tribune at one of the potential sites at 17th Avenue Northwest and 80th Street, where a new Greenway will be constructed in early 2015. Colwell said that the raingardens pair well with Greenways because the ends of streets bulb out and create a space where a bed fits nicely.
The project is anticipated to prevent an average of one million gallons of untreated sewage and stormwater per year from entering the Ship Canal and Salmon Bay. Construction is anticipated to begin in mid 2015.
Furthermore, the project is coupled with the RainWise Program, a natural drainage system program for private property owners. The idea is to supplement SPU’s block instillations with private property beds. Many Ballardites have already taken the City up on its offer of rebates for installation of raingardens.
In addition, SPU will be replacing an outfall pipe at one of the main stormwater outfall locations at the end of 24th Avenue Northwest. Currently a 30-inch diameter wooden pipe carries stormwater into Salmon Bay. Ballard’s other over flow site resides at the end of 28th Avenue Northwest.
For more information on the NDS project, visit the project website: www.seattle.gov/cso/ballard.