Flow Characteristics at a River Diversion Juncture and Implications for Juvenile Salmon Entrainment

Abstract

Flow structures at a river diversion juncture are complex and have been studied extensively. Their impact on the juvenile salmon entrainment into the side channel, however, is less investigated, and based mostly on empiricism. In this study, a Eulerian fish tracking model is developed and used in conjunction with a 3D flow solver to quantitatively evaluate the implications of complex flow characteristics at typical junctures on fish entrainment. First, the flow model is validated with the available experimental data, key flow structures are examined using the results, and their implications for fish entrainment are discussed. Next, the numerical fish tracking model is used to show that the cross-sectional fish distribution immediately upstream of a juncture is an important factor that controls fish entrainment efficiency. Fish entrainment efficiency curves are developed for different flow diversion ratios and fish distribution patterns and used to shed light on the reasons behind some field-observed fish entrainment patterns. 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, in agreement with field observations. 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.