Numerical Modeling of Flows at the Confluence of the Columbia and Pend d ’ Oreille Rivers

A high resolution three-dimensional numerical model, COCIRM, was adapted and optimized to predict the potential impact of the Waneta Expansion Project (WEP) on the flow conditions at the confluence of the Columbia and Pend d’Oreille rivers. Flows in this confluence area represent important habitat features for white sturgeon, including the well-developed low-speed Waneta Eddy for sturgeon rearing and feeding, and the jet-like high-speed Pend d’Oreille River outflow for sturgeon spawning. Extensive model calibrations and validations were carried out to render the model a useful and reliable tool for the WEP environmental impact assessment. The model results are in good agreement with extensive in situ observations in terms of the patterns of the Waneta Eddy, Pend d’Oreille outflow and its associated standing waves as well as water temperatures.