Spawning habitat rehabilitation ‐ II. Using hypothesis development and testing in design, Mokelumne river, California, U.S.A.

Abstract

Rehabilitation of salmonid spawning habitat in regulated rivers through spawning bed enhancement is commonly used to mitigate altered sediment and flow regimes and associated declines in salmonid communities. Partial design‐phase predictive results are reported from the application of SHIRA (Spawning Habitat Integrated Rehabilitation Approach) on the lower Mokelumne River, California. The primary management goal of the project was to improve habitat for spawning and incubation life stages of fall‐run chinook salmon (Oncorhynchus tshawytscha). In the summer of 2001, we conducted a pre‐project appraisal followed by development and testing of 12 design scenarios. A subsample of eight design hypotheses, used in three of the design scenarios, is presented. Hydrodynamic, habitat suitability and sediment entrainment model results were used to test five of the eight design hypotheses. Two of the three hypotheses not tested were due to inadequate data on flow boundary conditions at high discharges. In September 2001, the project was constructed in a 152 m reach of the LMR from a final design based on all eight of the design hypotheses presented. Transparent hypothesis development and testing in design is emphasized as opposed to declaring success or failure from an ongoing long‐term monitoring campaign of the case study presented.