Seattle Green Bridges for Salmon

The Aurora Bridge Project and the 5 bridges of the Seattle Ship Canal

For 80 years polluted runoff from Seattle’s Aurora Bridge has impacted Puget Sound’s migrating salmon.

Contaminated stormwater from Seattle’s Aurora Bridge has been discharged untreated to Seattle’s Lake Washington Ship Canal, impacting migrating salmon and resident orcas that depend on those salmon as a primary food source. That inspired environmentally innovative developer Mark Grey to join forces with Salmon-Safe to convene a multiple organization partnership to treat runoff through rain gardens, including at his Salmon-Safe certified Data 1 development project adjacent to the bridge.

Together with our partners, Salmon-Safe is creating a blueprint for managing the 2 million gallons that flow directly from the Aurora bridge into the ship canal between Lake Union and Puget Sound every year and, at the same time, developing an innovative model for a public-private partnership addressing contaminated stormwater from Pacific Northwest bridges.

Funded in part by Boeing, the Aurora Bridge project is presented by the following nonprofit partners: Salmon-Safe, Clean Lake Union, The Nature Conservancy in Washington, and Stewardship Partners. Primary technical partners include KPFF and Weber Thompson. For more information, please contact Ellen Southard with Salmon-Safe Puget Sound.

How to treat 2 million gallons of bridge runoff?

Building on the success of the Aurora Bridge project, Salmon-Safe has expanded work to other bridges on the Lake Washington Ship Canal. Our Green Bridges Pilot Study included the Ballard Bridge, Fremont Bridge, I-5 Bridge, University Bridge, and Montlake Bridge. With green infrastructure in mind, the scope of work was to determine the functionality of the existing runoff collection system, to quantify the extents of the collection basins, to develop new low impact development runoff collection and treatment strategies, and to locate adequate treatment sites. In all, our team determined that with this commitment to bioretention we could collect and treat 98 million gallons of runoff per year and reduce the detrimental impacts that bridge runoff has on this important salmon migration corridor.

Approximately 98 million gallons of untreated stormwater enter the Lake Washington Ship Canal by way of roadway runoff from the six bridges that span the waterway.

The plight of Puget Sound’s imperiled orcas highlights the importance for water quality and habitat protection for migrating Chinook salmon, the primary food source of the orca. The southern-resident orca population has been reduced to just 75 animals, in part because of declining populations of Chinook. For Salmon-Safe and our partners in the Seattle Green Bridges project, the plight of the orcas is another call to action to restore Puget Sound and its key tributaries.

Seattle Green Bridges Implementation Partners