Effect of diversion angle and vanes' skew angle on the hydro-morpho-dynamics of mobile-bed open-channel bifurcations controlled by submerged vane-fields

Abstract

The aim of this study was to characterize the impact of the diversion angle on the bed morphology, flow structure, and sediment fluxes at mobile-bed, open channel bifurcations, both uncontrolled and controlled with a submerged vane-field. The study also addressed the effects of the skew angle of the vanes and of the mobility of the diversion channel bed. For these purposes, 24 experiments were carried out with the diversion angles θ = {30°, 45°, 60°, 75°, 90°, 120°}. The recirculation zones in the diversion channel were classified according to their aspect ratios and two governing secondary circulations were identified inside these zones. In the presence of a vane-field, a strong vortex developed in the main channel all along the vane-field until past the diversion entrance. This vortex incorporated the main channel leg of the unique two-leg vortex that is otherwise identified in the absence of vanes at the downstream diversion corner. An independent diversion channel vortex replaced the diversion channel leg of the two-leg vortex. The best desilting efficiency was achieved for the diversion angle θ = 30°, regardless of the presence or the absence of vanes and the mobility of the diversion channel bed. In fully mobile-bed bifurcations, complete desilting was achieved for θ = 30° and α = 45°. This was also achieved for any of the tested skew angles, α = {15°, 45°}, when the diversion channel bed was rigid.