Evaluation of Potential Impacts of a Flood Storage Dam on Salmon Populations in the Chehalis River Basin

This presentation will describe an investigation of the potential effects of a flood storage dam on salmon populations in the Chehalis River Basin.  The flood storage facility is being evaluated by the Chehalis River Basin Flood Authority as one approach to alleviating the highly damaging flooding that occurs in the watershed.  Potential impacts to salmon populations are evaluating using science-based and transparent models, thus giving decision-makers informative and defensible results to base decisions upon.  Specifically, the investigation uses the SHIRAZ fish population simulation model to predict potential impacts resulting from changes in the watershed’s capacity to support salmon productivity and the productivity of the salmon populations.  The SHIRAZ model predicts capacity and productivity changes based on user-defined inputs to characterize the functional linkages between salmon habitat quantity and quality.  The functional linkages are based on empirical relationships established in scientific literature.  The data collection and modeling conducted to characterize potential changes in salmon with the installation of a dam include Physical Habitat Simulation Modeling (PHABSIM), water temperature, sediment transport, and large woody debris transport.