An experimental study of branching flow in open channels

Abstract Branching channel flow describes any side water withdrawals from rivers or main channels. Branching channels have widespread application in many practical projects, such as irrigation and drainage network systems, water and waste-water treatment plants, and many water resources projects. Therefore, in this research, a comprehensive analysis of laboratory data has been carried out to discover the best angle of branching. The study also aims to introduce simple, practical equations to help engineers of water resources to fix the percentage of discharge diverted to the branch channel. The study was carried out in the Irrigation and hydraulics laboratory of the civil department, Faculty of Engineering, Assiut University. The laboratory channel consisted of two parts, the main channel, and a branch channel. The main channel was 8.0 m in length, 20 cm wide, and 20 cm in depth. The division corner to the branch channel was sharp edged and located 5.0 m downstream of the main channel inlet. The branch channel was 3.0 m long, 20 cm in depth and its width was changed three times (10, 15, and 20 cm) respectively. A total of 84 runs were carried out. Investigations of the flow into the branching channel show that the branching discharge depends on many interlinked parameters. It increases with a decrease of the main channel flow velocity and the Froude number upstream of the branch channel junction. It also increases with an increase in the Yb / Yu ratio. In subcritical flow, water depth in the branch channel is always lower than the main channel water depth. The flow diversion to the branch channel leads to a decrease in water depth downstream of the main channel. In addition, the study showed that the highest discharge rate was obtained when the angle of branching was equal to 45° and then an angle of 60o. While the lowest discharge rate was obtained at an angle of 90°. Furthermore, at Br = 1.0, using a branching angle equal to 45° the discharge ratio (Qr) increases from about 4.42 to 19.01%, more than that obtained with using the branching angle equal 90°, while the discharge ratio (Qr) increases from about 0.52 to 49.18% and 1.51 to 24.79%, at Br = 0.75, and Br = 0.5 respectively.