Fish Habitat Enhancements for the Napa Creek Flood Protection Project

The Napa Creek Flood Protection Project will construct much-needed increases in flood conveyance through downtown Napa, using a system of flood bypasses and expanded floodplains.  The design of the project faced challenges to meet flood protection criteria while avoiding impacts to adjacent urban land use and preserving and enhancing riparian and aquatic habitat.  In particular, the project intends to provide enhanced passage and habitat for steelhead and salmon. This presentation describes the approach used on the Napa Creek project to identify opportunities and constraints for enhancing habitat in balance with flood protection objectives, and for selecting and designing improvements. The project used a risk-based approach to decide where channel stabilization was needed, considered a range of bio-technical measures to minimize the use of rock slope protection, and used geomorphic assessment and hydraulic modeling to assist in the selection and design of appropriate measures at each site.  Development of preliminary designs integrated field observations and analysis from fisheries biologists, riparian ecologists, and hydraulic engineers to propose improvements tailored to site-specific conditions.  This approach capitalized on opportunities to select measures that cost effectively meet both channel stabilization and habitat objectives on an urban creek.  The project design uses large woody material structures, vegetated reinforced slope stabilization, rock riffles, and vegetated floodplains.  Project designs were developed in a collaborative process with participation of eight federal, state, and local agencies.