PNNL

Abstract

Spatial and temporal distributions of dissolved gases in the Columbia and Snake rivers vary due to many factors including river channel and dam geometries, operational decisions, and natural variations in flow rates. As a result, the dissolved gas exposure histories experienced by migrating juvenile salmonids can vary significantly among individual fish. A discrete, particle-based model of individual fish movements and dissolved gas exposure history has been developed and applied to examine the effects of such variability on estimates of fish mortality. The model, called the Fish Individual-based Numerical Simulator or FINS, is linked to a two-dimensional (vertically-averaged) hydrodynamic simulator that quantifies local water velocity, temperature, and dissolved gas levels as a function of river flow rates and dam operations. Simulated gas exposure histories are then input to biological mortality models to predict the effects of various river configurations on fish injury and mortality due to dissolved gas supersaturation. This model framework provides a critical linkage between hydrodynamic models of the river system and models of biological effects. FINS model parameters were estimated and validated based on observations of individual fish movements collected using radiotelemetry methods during 1997 and 1998. The model was then used to simulate exposure histories under selected operational scenarios. We compare mortality rates estimated using the FINS model approach (incorporating individual behavior and spatial and temporal variability) to those estimated using average exposure times and levels as is done in traditional lumped-parameter model approaches.