Lower Yolo Ranch Restoration Project
cbec was contracted by Westlands Water District to develop the largest restoration project to date in the Lower Yolo Bypass in Yolo County, California.
The multi-benefit project includes modifications of up to approximately 2,127 acres of the 3,427-acre Lower Yolo Ranch. The Lower Yolo Restoration Project is located at the extreme southern end of the Yolo Bypass near the Cache Slough Complex and is within the jurisdiction of the Central Valley Flood Protection Board (CVFPB). The project is being completed in partial fulfillment of the contractors’ requirement to provide mitigation restoration for the endangered Delta Smelt. Project objectives are to:
- Enhance regional food web productivity in support of delta smelt recovery.
- Provide rearing habitats for out-migrating salmonids.
- Support a broad range of other aquatic and wetland-dependent species, including Sacramento splittail.
- Provide ecosystem functions associated with the combination of Delta freshwater aquatic/tidal marsh/floodplain/seasonal wetland/lowland grassland interfaces that existed historically.
Multiple field data collection activities were undertaken to support the restoration design and inform project construction. These consisted of:
- Water level, temperature and conductivity were monitored at sixteen locations to assess aquatic habitat resources, and understand inundation and tidal regimes. Groundwater levels were monitored at three locations.
- Numerous soil pits and six geotechnical borings were collected to understand the morphology of the site, and identify location specific features (i.e., duripans, massive clays).
- Multiple topographic and bathymetric surveys were also conducted over the life of the project to refine the LiDAR data and describe channel conditions. Surveys were often challenging due to the size and complexity of the site, and were mostly performed using RTK GPS technologies.
cbec developed a MIKE 21FM (2D flexible mesh) Tidal Hydrodynamic model for the restoration site and Cache Slough Complex to support the restoration design. Proposed tidal channel alignments and wetland enhancement areas were incorporated into the model to understand site inundation regimes, food web export, and select for channel geometries that provided in-channel velocities sufficient to promote self-maintenance and tidal prism conveyance. The model was also used to understand project impacts on water supply for irrigation and drainage and provide design solutions that supported existing demands. Restoration design grading plans and specifications (90%) were developed in 2013 and final design completed in 2018.
Restoration features included new tidal channels, berm breaches, new tide gates, new diversion structures, a relocated lift pump structure, new drainage ditches, and integration with irrigated agriculture. The project design is intended to accommodate sea level rise and provide ongoing resilience within the project site. Construction of the project, under a compressed schedule, began in August 2020 and was completed in October 2020. DWR, in conjunction with the California Department of Fish and Wildlife, will begin collecting monitoring data at the site in 2021.