The Ballard Basin projects combine Green Stormwater Infrastructure (GSI), also known as natural drainage systems (NDS), and future underground storage to prevent untreated sewage and stormwater from overflowing into Salmon Bay when it rains. Together, GSI and storage must provide approximately six million gallons of storage capacity in the basin to meet the regulatory target of no more than 1 overflow per year. Currently, overflows into the Ship Canal and Salmon Bay occur after as little as one-tenth of an inch of rain, and in 2013 Ballard accounted for over one-third of the entire city’s overflows.
Natural drainage system opportunities within Ballard include rain gardens, which are landscaped areas that allow stormwater to soak into the ground. By diverting runoff into the rain gardens and keeping it out of the piped sewer system, there is more capacity in the pipes to carry sewage to the treatment plant.
- Ballard Natural Drainage Phase 1 – this project constructed rain gardens along several streets to help reduce sewage overflows by keeping stormwater out of the sewer system. In 2012, we tested the performance of some of the rain gardens. Overall, the natural drainage systems that we tested reduced the amount of overflow into Salmon Bay, and also reduced peak flow rates by over 80%.
- Ballard Natural Drainage Phase 2 is currently in design on 22 additional blocks in the Loyal Heights Neighborhood. The project will prevent an average of 1 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.
We are collaborating closely with other city programs and departments, such as the Seattle Department of Transportation’s Safe Routes to School and Greenways programs, and with the Department of Neighborhoods coordinators in this district on pedestrian and intersection improvements.
The Washington State Environmental Policy Act (SEPA) Checklist and Determination of Non-Significance were issued on November 20, 2014. The environmental impacts of the proposed Ballard Natural Drainage Systems Phase 2 project have been analyzed and SPU has issued a Determination of Non-Significance:>
- SEPA Checklist (pdf)
- Determination of Non-Significance (pdf)
- Salmon Bay Outfall – SPU will be replacing an outfall pipe at the foot of 24th Ave. N.W., where an existing 30-inch diameter wooden pipe carries stormwater into Salmon Bay.
- RainWise is a natural drainage system program for private property owners. It offers rebates for property owners who install raingardens or cisterns on their property. View the eligibility area (pdf). Find out more.