Thornton Creek Culvert Strategy
Photo of Little Brook Creek that drains to Thornton Creek in Lake City showing a grate covered culvert underneath multi-family housing.
Seattle Public Utilities’ (SPU) mission is to foster a healthy environment for today and future generations, which includes caring for fish-bearing creeks. SPU has spent many years studying and partnering with academic researchers to better understand Seattle’s urban creek watersheds. Building on this research, the Thornton Culvert Strategy will develop a strategic plan for addressing creek culverts that are fish passage barriers in the Thornton Creek Watershed.
Thornton Creek and its tributaries flow under roads, through creek culverts, and across public and private properties. A creek culvert is a pipe or a box shaped channel, that allows the creek to flow under roads, sidewalks, trails, and public and private property. Creek culverts can be a barrier to fish passage if they are too steep, too small, too long, damaged, have grates that block fish, or water flows through them too quickly. Removing these fish passage barriers will help salmon and other fish reach important spawning areas.
Learn more about Creek Culverts in Seattle
The Thornton Creek Culvert Strategy will:
- Reduce flooding, improve drainage, and improve creek health and habitat by removing fish passage barriers
- Evaluate and prioritize creek culvert and fish passage barrier removal projects that benefit salmon and other fish
- Develop a plan to address urgent and emergency creek culverts that are fish passage barriers
- Build an effective approach that can be applied to other fish-bearing creeks across the city
- Engage equitably and partner with Tribal governments, community, regulatory agencies, and state partners
The Analysis Phase (2026) will focus on identifying data gaps, stakeholders, and Tribal partners. In this phase, the team will build an equitable engagement plan with guidance from SPU’s Racial Equity Team, Tribal Liaisons, and Department of Neighborhoods Equity and Engagement Advisor.
The Data Collection Phase (2026) includes data collection identified in the previous phase, both desktop analysis and fieldwork. In this phase, the team will finalize the engagement plan.
The Planning Phase (2026) will prioritize development, evaluation, and selection of a preferred strategy. Coordination and collaboration with key regulators, Tribal governments, state partners, and community will happen in this phase.
The Implementation Phase (2027 and beyond) will focus on initiating and constructing the creek culvert projects identified by the Thornton Culvert Strategy. There will be ongoing outreach to Tribal governments and state regulatory partners.
Thornton Creek drains a 7,402 acre (11sq. Mile) urban watershed in King County between Puget Sound and Lake Washington, extending roughly from NE 190th St in the City of Shoreline to NE 80th St in the City of Seattle. The watershed contains diverse settings including a large, mature conifer forest in Hamlin Park, busy stretches of I-5 adjacent to the Northgate Mall area, steep ravines, dense multifamily neighborhoods, retail corridors, and residential neighborhoods with large, wooded lots.
Over the last 170 years, the watershed’s native forest has been replaced by urban development. Over 90% of Thornton creek (more than 15 miles) flows above ground, through more than 700 backyards and over 15 parks and natural areas. Thornton creek is mainly un-piped and flows above ground, unlike most urban watersheds in Seattle. This diverse system supports a variety of wildlife, plant life, and the remnants of once abundant salmon runs.
Salmon runs remain a key cultural cornerstone for the Native Tribes that traditionally inhabited this land and relied on salmon as a cultural resource. The Treaty of Point Elliott enshrined the right to fish for Tribes with Usual and Accustomed fishing areas. This understanding was further upheld by US v Washington (1974, “Boldt Decision”) affirming Tribal rights to half of the salmon harvest and as state co-management of fisheries. The culvert case led to work to remove fish passage barriers on creeks and increase accessible salmon habitat on state owned land.