The Effect of Diversion Angle on Flow Pattern and Sediments Transportation around the Intake Mouth in Sinuous River

Secondary current in the river bend causes transportation of the river bed sediments towards the convex bank. Several parameters affect the rate of sediment diversion to the intake. In this research, the effects of intake angle on sediment rate were investigated in two extreme angles, 52 degrees (the gentle angle) and 90 degrees (the sharp angle), under various discharges and flow diversion rates. The results show that the outflow capacity of intake in 52-degree is higher than 90-degree about 21 percent for various discharges. Therefore, it is possible to decreases the width of intake mouth in 52⁰ diversion angle proportionally. Comparison of the sediment diversion rates in two angles shows that, in case of intake with 90-degree diversions angle, up to 22 percent, less sediment diverts into intake mouth, compared with 52-degree diversion angle. At this angle because of the quick rotation of flow surface towards intake mouth, the angle between surface flow and bottom flow increases (about 90 degree), and the power of secondary flow, increases, and consequently decreases sediment entry into intake. Secondary flow power in intake mouth causes by secondary flow in the bend and diversions angle that is identified by Psec Index. By increasing the flow rate diversion in 90⁰ diversions angle, the domain of flow diverted into the intake mouth expands more than the width of bend and approaches to the moving sediment bar in the inner part of the bend. This flow acts the same as flow in the outer bend of the river but with higher potential for sediment transportation progression. At the 52-degree angle, the flow rotates with a minimized angle by diverting a part of river flow into the outer bend. Therefore, at the lower angle in flow diversion and intake alignment, the power of secondary flow becomes weaker than the 90-degree angle. This results in lower rate of up to 22 percent more sediment diversion into the intake compared with 90-degree diversion angle.