Case Studies on the Use of LIDAR Data for Hydraulic Modeling of Upstream Fish Passage

ABSTRACT The evaluation of fish passage in shallow‐braided rivers is difficult due to flashy flows and changing bed topography. In such systems, timing of data collection at specific flows suitable for migration are not feasible due to safety and/or logistics of not being able to sample a sufficient number of potentially critical riffles and changes to the channel between sampling events. Hydraulic modeling using high resolution LIDAR data is a robust way to address these challenges. LIDAR data, supplemented by survey‐grade real time kinematic global positioning system and total station 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 Ventura River, Ventura County, California, USA. For the Santa Clara River, Ventura County, California, USA, LIDAR data was the sole basis for the topography for 3 two‐dimensional HEC‐RAS models of upstream passage of adult steelhead, since the entire channel was dry when the LIDAR data was collected. 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 on each stream. A minimum passage depth criterion of 0.21 m was used for adult steelhead. The results of the predictive modeling will be used by the California Department of Fish and Wildlife to identify flow criteria that protect migrating upstream steelhead.