Optimal flow pattern around hybrid groins with various orientations to improve fish habitat via Experimental Investigation using Acoustic Doppler Velocimeter

Abstract

Given the growing interest in river restoration and natural river improvement, groins are recommended as an essential hydraulic component for creating riparian habitats and controlling local flow. The optimum design of groins for environmental purposes is still not defined despite its long history of improving river flow dynamics. The primary goal of this paper is to determine the influence of hybrid groins' orientation angle and geometry on both the flow velocity and structure to enhance fish habitat. This study investigates six models of unsubmerged hybrid L-shape groins installed in a straight channel with a deformed bed. The hybrid L-shape groins consist of two parts, an impermeable part that objected to the flow, and a permeable one (piles rows) arranged in the flow direction. The influences of groin's both contraction/length ratio and orientation angle on the flow velocity and structure are studied. The contraction ratio represents the impermeable groin length relative to channel width (W/B), while the orientation angle (θ) is the groin inclination angle in the up/downstream direction. Groin models with 25% contraction ratio and up/downstream orientation angle (θ) of 45°, 60°, and 90° were used. Groin with an orientation angle of 45° toward downstream has introduced the highest reduction on the flow velocities. Also, groin with θ=90° downstream introduced low velocities, but these velocities still more than the reduction of 45° case. The area of the dead zone -the zone of low velocities-in the case of θ=45° is about 70 % more than that of θ=90°.