Bear River Levee Setback Project
Prior to joining cbec, select cbec staff members provided geomorphic and ecosystem enhancement services to the Three Rivers Levee Improvement Authority (TRLIA) on the Bear River Levee Setback Project.
This project was designed to replace an existing levee that was weakened by major structural deficiencies, and to provide a 200-year level of flood protection. The project spanned 9,600 feet and replaced portions of the Bear River and Feather River levees at the confluence of the two rivers. The old levees were removed and used for construction of the new setback levee. Approximately 600 acres of wildlife habitat were created, benefiting several threatened and endangered species, including Swainson’s hawk, valley elderberry longhorn beetle, and Chinook salmon. Project feasibility and design commenced in 2005 with implementation of the complete project in 2007. The levee setback project was the first of its kind in the Central Valley of California, and includes multi-objective, holistic, floodplain management elements such as:
- Flood risk reduction, through protection of nearby development by the new setback levee, and reduction of the water surface elevation of peak flood events due to increased conveyance capacity provided by the increased floodplain area.
- Ecosystem enhancement opportunities through riparian restoration of the newly exposed floodplain in the setback area, construction of a fish habitat, backwater swale at the downstream end of the project floodplain, and Giant Garter Snake and Swainson’s Hawk habitat in native grassland areas planted as part of the restoration project.
Select cbec staff members directed technical geomorphic reconnaissance and studies, including RMA2 (2-D) modeling and SED2D sediment transport analyses. These quantified the transport regime of the setback floodplain and associated the main channel of the Bear River in comparison to the pre-project conditions. These analyses resulted in several key technical elements of the project, including a sacrificial erosion berm at the toe of the new levee, and design elements for the fish habitat swale. The swale was constructed in order to drain the floodplain during the receding limb of the hydrograph, in addition to providing backwater habitat.