Validation of Chinook fry behavior‐based escape cover modeling in the lower Klamath River

An emerging trend in the state-of-the-art instream flow assessment applications is the use of three-dimensional channel topography coupled with two-dimensional hydrodynamic models. These components are most often integrated with biological response functions for depth, velocity, and substrate to simulate physical habitat for target species and life stages. These approaches typically involve the simple extension of the one-dimensional conceptual habitat models represented by the Physical Habitat Simulation System (PHABSIM) developed by the U.S. Fish and Wildlife Service (Stalnaker, 1995). However, as demonstrated in this paper, the physical habitat based template represented by high-resolution channel topography and two-dimensional hydrodynamic model outputs can extend these simple conceptual models of habitat to incorporate additional behavior-based decision rules. The approach demonstrated in this paper evaluates the spatial suitability of physical habitat for chinook fry based on the incorporation of behavioral rule sets associated with instream object cover (i.e., velocity refuges) and in-water escape cover type and distance. Simulation results are compared to simplistic based physical habitat simulations using only depth, velocity, and substrate and validated against independent fish observation data. Results demonstrate that the functional relationship between predicted habitat and discharge utilized in many instream flow assessments is significantly different when the additional behavior-based decision rules are applied.