Mill Creek Passage - Gose St Conceptual Design

This project completed conceptual designs on Mill Creek at the downstream end of the flood control channel, west of the City of Walla Walla in Walla Walla County. The contracted engineering firm Waterfall Engineering provided thirty percent basis of design report and plan set documents including estimated quantities and cost estimates. The design process included a geomorphic analysis that determined a sediment budget was not needed and expanded the scope to extend downstream. Four alternatives were selected and developed to a comparable design level. Stakeholders were engaged and a preferred alternative was selected to develop to thirty percent.

This section of the Mill Creek is identified by the Snake River Recovery Board as a priority restoration reach and major spawning area. Adult and juvenile summer steelhead and spring Chinook occupy this project reach during migration, and bull trout occur here seasonally. Other species of cultural value and state concern (lamprey, margined sculpin, and leopard dace) inhabit this location.

The Mill Creek channel at Gose St in Walla Walla, WA is configured so that fish passage, flood protection, and secure infrastructure are provided in a long-term, low-maintenance manner. This project is the first step toward this goal by assessing and creating a conceptual design to improve the interface between the natural channel and flood control channel at the project location. This work will provide improvements for Snake River steelhead and spring Chinook.