Experimental investigation of scour at a channel junctions of different diversion angles and bed width ratios

Abstract

Diversion flows from rivers or main channels affect bed morphology and cause erosion and sedimentation at the diversion channel junction. In a diversion channel flow system, the scour depth and scour length are considered important parameters and should be taken into account during the project construction stage because it affect the stability of main channel banks and crossing structures. In this study, the scour depth produced by diversion flow in a main channel was investigated using a physical sand bed model. The investigations considered five diversion angles (30°, 45°, 60°, 75°, and 90°), three bed width ratios (29%, 38%, and 48%), and five total discharges (7.25, 8.5, 9.75, 11, and 12.25 L/s). Results indicated that the scour depth in the main channel reduced as the diversion angle reduced. Empirical relationship to demonstrate relative scour depth (Kds) for different diversion angles and bed width ratios was proposed. Relative scour depth can be defined as a relative scour depth in case of a diversion angle of θ°to that with 90°for the same flow condition and bed width ratio. Empirical relationships to estimate the scour depth and scour length with the governing hydraulic parameters were also established with a good accuracy. Testing the proposed relationships gave reasonable mean errors of 3.46% and 10.3% in predicting scour depth and scour length, respectively.

Enhancing the Flow Characteristics in a Branching Channel Based on a Two-Dimensional Depth-Averaged Flow Model

“…The results of the simulation with and without obstacles show that the velocity at the upstream location of the junction is always higher than the velocity downstream. The low velocity zones that were recognised at the branching channel of the Tigris River were also observed in other experimental studies [8,16] and denoted as flow separation zones. The first low-velocity zone appears in the main river opposite to the branching channel entrance downstream of the junction.…”

“…For movable bed and sediment transport, knowledge of the threshold point of the sediment particles to be in motion is essential, and most existing studies represent the threshold point of sediment particles in terms of critical mean velocity, V c . Many methods can be used for estimating critical mean velocity, of which the Simons andŞentürk method, which is shown in Equation 3, is one of the most common [16,40].…”

“…However, an increase in branching angle from 45° to 90° leads to movement of the separation zone downstream in the branch channel. The smallest separation zone occurred when the branching angle was 30° [16]. Separation zone (2) is formed near the right bank in the main channel and downstream of the branching junction as shown in Figure 1.…”

“…These vortexes played a major role in changing the bed morphology in the main and diversion channels. Alomari et al [16] designated that the branching angle should be decreased as much as possible to decrease the scour depth. They conducted experiments with different diversion angles (30°, 45°, 60°, 75°, and 90°) and observed that the minimum scour depth was associated with a diversion angle of 30°.…”

Improving the Hydro-Morpho Dynamics of A River Confluence by Using Vanes

“…For moveable bed and sediment transport, knowing the threshold point of sediment particles in motion is important, and most existent studies represented the threshold point of sediment particles in terms of critical mean velocity, namely, V c . Many methods are available for estimating the critical mean velocity, and one of the most common ones is the Simons andŞentürk method, which is shown in Equation 3 [47,48].…”