Experimental and numerical studies on deflector configuration in straight flood channel for heterogeneous flow enhancement and fish habitat improvements

Abstract

For ecological restoration of concrete flood channels, installing current deflectors is a straightforward, cost-effective, and efficient approach with minimal maintenance. It is important to find the appropriate arrangement, orientation, number, protrusion length, width, and spacing of deflectors to achieve an effective flow pattern. In this research, indoor flume experiments were carried out to identify the flow conditions and fish trajectories in the absence and presence of deflectors. Deflectors were found to enhance the flow heterogeneity and benefit the upstream movement of fish in the floodway. To further optimize the design, a 2D numerical simulation was conducted to predict the effectiveness of different deflector configurations. The results showed that compared with aligned deflectors or solid triangles, staggered deflectors and central islands were more suitable for the creation of non-uniform flows and pool areas. The optimum orientation of deflectors was perpendicular to the flow. A set of four deflectors with appropriate intervals along the channel was highly recommended. It was found that the ideal contraction ratio (α= deflector length / channel width) was between 25% and 50% to protect the river bank and bed from erosion. As the width of the deflector had less effect on the flow pattern, the narrowest deflector with a ratio (β) between deflector width and channel width of approximately 17%, was found to be preferable considering the construction cost. The ratio (γ) between deflector spacing and channel width was proposed to be set from 1.67 to 2.5 for flow concentration and sinuosity generation.