COMPARISON OF METHODS FOR ANALYSING SALMON HABITAT REHABILITATION DESIGNS FOR REGULATED RIVERS

River restoration practices aiming to sustain wild salmonid populations have received considerable attention in the United States and abroad, as cumulative anthropogenic impacts have caused fish population declines. An accurate representation of local depth and velocity in designs of spatially complex riffle-pool units is paramount for evaluating such stability. In this study, three models for predicting channel hydraulics-1D analytical, 1D numerical and 2D numerical-were compared for two theoretical spawning habitat rehabilitation (SHR) designs at two discharges to constrain the utility of these models for use in river restoration design evaluation. Hydraulic predictions from each method were used in the same physical habitat quality and sediment transport regime equations to determine how deviations propagated through those highly nonlinear functions to influence site assessments. The results showed that riffle-pool hydraulics, sediment transport regime and physical habitat quality were very poorly estimated using the 1D analytical method. The 1D and 2D numerical models and capture characteristic longitudinal profiles in cross-sectionally averaged variables. The deviation of bath 1D approaches from the spatially distributed 2D model was found to be greatest at the low discharge for an oblique riffle crest with converging cross-stream flow vectors. As decision making for river rehabilitation is dependent on methods used to evaluate designs, this analysis provides managers with an awareness of the limitations used in developing designs and recommendations using the tested methods. Copyrights (C) 2008 John Wiley & Sons, Ltd.