Feather River West Levee Program Cutoff Walls

The Feather River watershed basin, located 50 miles north of Sacramento, California, is home to agriculture-producing communities, including Yuba City, Live Oak, Gridley, and Biggs. These communities are protected by levees that were historically prone to under-seepage and through-seepage deficiencies, leading to catastrophic levee failures in 1955, 1986, and 1997.

In response to these risks, the Sutter Butte Flood Control Agency (SBFCA) initiated the Feather River West Levee (FRWL) Program in 2010 to upgrade 35 miles of levee infrastructure to comply with Federal and State standards for urban flood protection. The program aimed to provide 200-year flood protection to more than 34,000 at-risk properties classified within FEMA Special Flood Hazard Areas.

The primary technical challenge was constructing 7,744,803 square feet (SF) of cutoff walls to address seepage deficiencies. Specific challenges included depth requirements, with conventional excavation reaching depths up to 85 feet but deeper sections requiring advanced techniques such as Deep Soil Mixing (DSM) to depths exceeding 120 feet.

Unanticipated depth changes in competent keys required modifications to methodologies. Historical levees contained Native American archaeological sites, necessitating delays and redesigns for preservation. The specialized cutoff wall construction industry faced labor and equipment shortages due to the project’s magnitude and timeline constraints. Tight work windows between April and November to avoid flood risks demanded accelerated construction schedules.

Advanced construction techniques included conventional excavation for depths up to 85 feet, leveraging custom-built long-reach excavators for efficient trenching and backfilling. Deep Mixing Method (DMM) was used for depths exceeding 85 feet, providing structural integrity and low permeability with soil-cement-bentonite mixtures.

Quality control and design innovations were developed, including site-specific mix designs using boring logs to ensure optimal backfill gradation and permeability. Rigorous testing standards based on ASTM and API protocols were employed, along with settlement plates and permeability testing to monitor and verify performance.

An archaeological preservation plan was implemented, partnering with regulatory agencies, tribes, and contractors to address archaeological findings. Construction sequencing was adopted that allowed work around sensitive sites while enabling artifact recovery post-construction.

Adaptable construction planning was adopted to adjust methodologies based on verification drilling and geotechnical findings. Custom excavation techniques were developed for tight corners and restricted alignments using cross-excavation designs.

The Feather River West Levee Program achieved its primary objectives, delivering robust flood protection infrastructure while overcoming significant challenges.

The project successfully reduced flood risk by constructing 6,974,926 SF of conventional excavation cutoff walls and 769,877 SF of DSM walls, addressing seepage vulnerabilities. It elevated 35 miles of levee to meet 200-year flood protection standards, safeguarding over 34,000 properties.

Compliance and quality assurance were ensured through achieving permeability rates as low as 5×10-8 cm/sec, surpassing the required 5×10-7 cm/sec standard. The project delivered uniform cutoff wall thicknesses (36 inches for excavation and 27 inches for DSM), ensuring structural integrity and compliance with Federal and State standards.

Cultural sensitivity and collaboration were prioritized through the development and implementation of site-specific archaeological treatment plans, preserving historical artifacts and maintaining positive relationships with local tribes.

Resource and schedule management were optimized, enabling the completion of 4.5 million SF of cutoff walls in a single season—the largest levee construction effort in California—despite labor and equipment limitations. Productivity was maintained through strategic subcontracting and collaboration, meeting seasonal constraints and contract deadlines.

Lessons learned highlighted the need for enhanced pre-construction archaeological investigations and geotechnical verification to reduce delays. The project demonstrated the value of JV partnerships and subcontractor integration for resource-intensive projects.