Modeling embryo survival affected by sediment depositioninto salmonid spawning gravels:Application to flushing flow prescriptions

This paper presents a framework for predicting embryo survival in salmonid spawning gravels as a function of sediment deposition. This framework integrates three quantitative relationships modeling the variations of substrate permeability with sediment deposition, apparent velocity with substrate permeability, and embryo survival rate with apparent velocity. The model allows evaluation of the impacts of sediment deposition on embryo survival. The relative sensitivity of embryo survival to three selected environmental factors is investigated. The model results indicate that embryo survival is most sensitive to the composition of fine sediments (or sediment-gravel size ratio). The maximum influences of the hydraulic pressure head and the length of intragravel flow path are ;60 and 35% of the value influenced by size ratio. The proposed model is applied to determine the timing of flushing flows. The results suggest that the interval between flushing flows should be reduced when higher levels of embryo survival are prescribed or higher near-bed sediment concentrations are imposed.