Abstract: The main purpose of this study was to investigate the uniformity of sediment transporting flows into bilateral intakes on both sides of a spillway and compare it with a single intake either in outer or inner bend. The results indicated that most of the sediment deposition is towards the inner-bend intake. In the case of a single intake structure, the comparative results with the bilateral intakes indicated that both the water inflow rate and sediment entrainment increase in the case of a single intake located on the outer bend. In the case of a single intake on the inner bend, the water inflow rate decreases, but the inward-sediment load increases. It is necessary to use both the intake sill and sluice way to control the sediments entering the intakes, especially for the inner-bend intake.

Introduction: Diversion of sediment transporting flows is one of the challenges in river hydraulics and engineering works. There is a number of evidence for the construction of weirs and diversion dams in river bends, and sometimes locating water intakes on one or two sides of the river bend is needed. However, this encounters problems in terms of asymmetry of flow distribution into the inner- and outer-bend intake structures. Most of the previous studies have been conducted under clear-water flow conditions. The main purpose of this study was to investigate the uniformity of sediment transporting flows into bilateral intakes on both sides of a spillway and compare it with a single intake either in outer or inner bends.

Methodology: In this study, FLOW-3D numerical model was used to simulate sediment transport flow into bilateral intakes on one and both sides of a diversion dam in a channel bend. The geometric conditions of modeling were considered based on the laboratory study of Farhadi-Bansuleh and Yasi (2019). The laboratory channel was a rectangular channel with a 90o bend. The experiments were carried out under clear water flow conditions. The numerical model was first calibrated and validated for the physical model conditions; and then adjusted for sediment transporting flows. In the lack of physical data for sediment transporting flows into the bend intakes, the modeling results were evaluated based on hydraulic engineering judgments.

Results and Discussion: The results of the simulation for taking water from both sides of the weir with an angle of 90 degrees show that with the presence of the sill and the sluiceway, the mean inflow rate to intakes in the outer and inner intake was 0.021 and 0.016 (m3/s), respectively. Mean sediment load into the outer and inner intakes was calculated to be 0.0012 and 0.007 kg/s, respectively. The corresponding total sediment load was 0.01 and 0.55 kg, respectively. The ratios of the water inflow, the mean sediment load and the total sediment load in the outer intake compared to the inner intake were 1.31, 0.17 and 0.018, respectively. Also, the flow patterns upstream of the weir showed that the creation of secondary and spiral currents in the inner channel bend causes sedimentation in this part and eliminates the flows into the inner intake. Comparison of the simulation results of water intake from both sides and one side of the diversion dam in the outer intake showed that the flow rate increased by 0.002 (m3/s), while this value decreased up to 0.001 (m3/s) in the inner intake. In the outer intake, the mean sediment load and the total sediment volume to intakes increased by 0.0008 (kg/s) and 0.002 (kg) respectively. The increase for the inner intake was 0.0015 (kg/s) and 0.06 (kg), respectively.

Conclusion: The results indicated that the weir position at an angle of 60 degrees from the bend inlet, and 90-degree intakes are more efficient due to less sediment entry and uniform inflow distribution to both bilateral intakes. The model was run for three scenarios (i.e. with bilateral intakes, and with a single intake in outer or inner bend). The results indicated that most of the sediment deposition is towards the inner-bend intake. In the case of a single intake structure, the comparative results with the bilateral intakes indicated that both the water inflow rate and sediment entrainment increase in the case of a single intake located on the outer bend. In the case of a single intake on the inner bend, the water inflow rate decreases, but the inward-sediment load increases. It is necessary to use both the intake sill and sluice way to control the sediments entering the intakes, especially for the inner-bend intake.