Understanding Juvenile Salmon Entrainment at River Junctures through Numerical Modeling

Flow features are complex at river junctures and it has been studied extensively in the past. The juvenile salmon entrainment into the side channel at river junctures, however, is less investigated; previous studies relied mostly on empirical approaches. In this talk, we present a numerical modeling approach in which a 3D flow solver is used for flows and a numerical fish track model is developed to assess the implications of the fish entrainment at junctures. First, the flow model is validated with the available experimental data, key flow structures are discussed, and the implications for fish entrainment are discussed. Next, the numerical model is used to show that the cross-sectional fish distribution upstream of a juncture is an important factor for fish entrainment efficiency. Fish entrainment efficiency curves are developed and they are compared with the field measured fish tracking data. Further, the model is used to show that the secondary flow in a river bend may have a significant impact on fish entrainment at flow junctures. Finally, a submerged vane is demonstrated to be a potential management option to locally generate secondary flows upstream of a juncture to achieve the desired fish entrainment property.