Japanese Gulch Creek Fish Passage Design and Habitat Restoration

  • Before: Junction box between culverts poses major fish passage challenge.
  • After: Baffle installation enhances fish passage conditions for coho salmon.
  • Before: Raised culvert under railroad grade poses fish passage challenge.
  • Juvenile coho salmon – what it’s all about
  • After: Engineered fish ladder provides adequate fish passage for coho salmon.

Confluence Environmental Company led a team to address fish passage and habitat restoration on Japanese Gulch Creek. The original scope of the project was to improve fish passage in a concrete junction box between upstream and downstream culverts, where streamflow was spread over a concrete apron in a very thin layer that was a severe impediment to upstream adult fish passage. Confluence assessed the creek drainage and identified additional fish passage barriers upstream that would limit access to usable habitat should this initial barrier to passage be removed. This finding led to change in the scope of the project.


Basing our approach on an overall assessment of the conditions in the lower part of the Japanese Gulch Creek watershed allowed the team to identify multiple opportunities for fish passage improvement. To address the original project – the passage barrier posed by the junction box – the team developed a low-cost design combining baffles and boulders, which were field-engineered for maximum placement, to focus and deepen the flow of water. Cost of this design was significantly lower than the original budget, creating the opportunity for future phases. Fully funded additional phases included engineering a stacked-culvert fish ladder to improve fish passage at a perched culvert, and realigning the stream to a historical channel discovered during the watershed conditions assessment. Seed money allowed pursuit of a fourth phase requested by the Tulalip Tribes: reconnection of the creek to a nearby wetland for juvenile salmonid rearing. After funding was obtained, the Confluence team designed a fish ladder at the mouth of the Japanese Gulch Wetland where the outfall flows into Japanese Gulch Creek, making valuable off-channel habitat available for juvenile rearing. Currently, in Phase 5, Confluence is providing ecological input to the development of conceptual and preliminary designs for the tidal restoration of Japanese Gulch Creek estuary and assisting with securing grant funding.


Working closely with our team members and the City of Mukilteo staff, Confluence developed a plan to address the passage barrier in the junction box for a fraction of the initial cost projected by the City Engineer. This freed up project budget to address another upstream passage barrier in the form of a perched culvert. The team developed a cost effective solution to this barrier as well. In addition, the stream assessment identified a historical  channel that Confluence believes was abandoned 40 to 60 years ago. The team developed a conceptual design to move the stream from its existing heavily engineered channel (three concrete weirs and a concrete flume) back to its historical channel thereby bypassing three additional passage barriers and opening up more than twice the length of channel and habitat for future fish use.

Project Location
Mukilteo, Washington

City of Mukilteo

Project Timeline
June 2009 – Ongoing