Evaluating Upstream Fish Passage in Sand Bed Channels

ABSTRACT The evaluation of fish passage in sand bed channels is challenging due to rapidly changing bed topography. Traditional empirical and hydraulic modeling approaches are not appropriate for such systems because they assume a fixed channel bed. Hydraulic modeling using sediment transport equations is a robust way to address these challenges, since the sediment transport equations can explicitly simulate changes in the channel bed due to flows. High‐resolution LIDAR data was used as the basis for the topography for a two‐dimensional HEC‐RAS model of upstream passage of adult steelhead ( Oncorhynchus mykiss ) on the Santa Maria River, Santa Barbara/San Luis Obispo County, California, USA. The model was run for both fixed and mobile bed conditions. The results of the HEC‐RAS models were used to identify flow levels that met the minimum depth and width thresholds needed for adult steelhead to migrate upstream through the study reach. The results of the predictive modeling will be used by the California Department of Fish and Wildlife to identify flow criteria that protect upstream migrating steelhead.