Lower Yolo Ranch Tidal 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 2,149 acres of the 3,427-acre Lower Yolo Ranch.

In conjunction with the California Department of Water Resources, Westlands Water District, Hallmark Group, and ICF, cbec eco engineering designed, permitted, and constructed a 2,149 acre tidal marsh restoration project in the Lower Yolo Bypass near the Cache Slough Complex. The goal of the project was to benefit native fish, including delta smelt (Hypomesus transpacificus), and winter- and spring-run salmonids, along with supporting a broad range of other aquatic and wetland-dependent species (including Sacramento splittail) and providing ecosystem functions associated with the combination of Delta freshwater aquatic/tidal marsh/floodplain/seasonal wetland/lowland grassland interfaces that existed historically.

Project site immediately after construction in 2020 (top), 8 months post-construction (middle), and flourishing site in 2023 (bottom).

The Lower Yolo Ranch Tidal Restoration Project, which adjoins the Yolo Flyway Farms tidal marsh restoration project (completed in 2018), represents a significant milestone with the completion of a ‘turn key’ tidal marsh restoration project. This partially fulfills mitigation obligations associated with the ongoing operation of the State and Federal Water Projects, which both deliver irrigation and municipal water to Central and Southern California.

The design development and entitlement of the project was overseen by the multi-agency Fish Agency Strategy Team, or FAST, which is tasked with approving mitigation for the ongoing need. The Lower Yolo Restoration Project was designed to take advantage of the large areas of the site that were at ideal elevations for tidal marsh restoration, and that would contribute to the food web of the Cache Slough Complex quickly and without large amounts of earthwork. Construction of the project, under a compressed schedule, began in August 2020 and was completed in October 2020.

During the course of the project, multiple field data collection activities were undertaken to support the restoration design and inform project construction (i.e., water levels and water quality, numerous soil pits and several geotechnical borings, multiple topographic and bathymetric surveys. These data were ultimately used with a 2D hydrodynamic model to understand the performance of proposed restoration concepts and potential impacts on flood

conveyance and offsite water supply. The preferred restoration approach was formalized following alternatives evaluation December 2012 (as informed by the scientific experts from regulatory agencies on the FAST technical advisory committee). The design concentrated on a substantially reduced earthwork footprint and volume, in part to provide resilience to sea level rise. Restoration design grading plans and specifications were finalized in January 2020 and called for 270,000 cubic yards of balanced earthwork comprising excavation of tidal channels, skim grading, berm breaches, shallow transitional upland fills, with the balance used to construct a perimeter berm for access. Four M Contracting was selected to construct the project.