Part of the California Natural Resources Agency’s California EcoRestore initiative, this fish exclusion project aimed to improve the operations of Wallace Weir, as well as implement a fish trapping facility to prevent adult salmon entry into the Colusa Basin Drain.

Wallace Weir controls water surface elevations in Knights Land Ridge Cut needed to provide irrigation water to surrounding agricultural operations. Salmon and sturgeon migrating upstream through the Yolo Bypass can be fatally cued by attraction flows into Knights Landing Ridge Cut where a combination of warm temperatures, poor water quality, limited habitat and a lack of upstream return access to the Sacramento River (except during high flows) result in mortality. Working with Kjeldsen, Sinnock & Neudeck, Inc., cbec prepared hydraulic and flood impact analyses to support the 408 Certification and Central Valley Flood Protection Board Permit by modifying and calibrating the Central Valley Floodplain Evaluation and Delineation Program HEC-RAS model in the vicinity of Wallace Weir to assess project performance over a range of flow conditions. cbec staff performed HEC-RAS simulations to assure compliance of fish collection facility hydraulics to NMFS Anadromous Salmonid Passage Facility Design Criteria and to optimize weir gate operations over a range of flows. Analyses included evaluation of entrance jump height, maximum velocities in different facility elements, additional hydraulic considerations and dissolved oxygen levels needed to support salmonids during relevant seasons.

cbec’s engineering, design, and permitting assistance informed construction in 2016, with monitoring ongoing.