Experiments on sediment characteristics in a desilting channel with a swirling flow

Abstract: The desilting channel with a swirling flow is an alternative novel technology for the water-sediment separation. The reason is that the swirling flow can be used to effectively separate the water and sediment. The obstruction of water diversion channels and abrasion of hydraulic machinery can also be reduced when diverting the water from sediment-laden rivers. This study aims to clarify the impact of different water and sediment conditions on the sediment characteristics in the desilting channel with a swirling flow. The physical tests were carried out to determine the expelled, the residual, and the deposited sediment along the downstream of the channel. In addition, the sediment trapping efficiency was evaluated under the incoming flow rate, the incoming flow velocity, the sediment gradation, and the hydraulic conditions. The results indicated that there was a regular variation in the sediment characteristics in the desilting channel with a swirling flow under the incoming flow. Specifically, the mass of expelled sediment decreased, when the incoming flow rates or the velocity increased, or the median particle size of incoming sediment decreased during this time. By contrast, the residual sediment mass increased to change the inflow rate during the sediment trapping, where the maximum variation amplitude was 16.3%. There was a great difference in the expelled sediment mass and the residual sediment mass of fine sediment with a particle size of 0.075-0.315 mm under various water and sediment conditions. The residual sediment was dominated in the downstream channel in the particle size range. Nevertheless, there was little difference in the removal of the sediment with the particle size >0.315-3.0 mm, as the water and sediment conditions changed. The mass of the deposited sediment in the sediment transport pipe increased with the increase of the incoming flow rate and the median particle size of sediment but decreased with the increase of the incoming flow velocity in the upstream channel. The maximum mass of the deposited sediment only accounted for 2.6% of the total incoming sediment. The performance of the desilting channel with a swirling flow was further improved to install the water eliminator in the downstream of the channel, especially in the removal of sediment with a particle size >0.16-0.315 mm. The sediment trapping efficiency increased by 4.6 percentage points, compared with that without the water eliminator. The sediment deposition was also reduced in the discharge tunnel. The desilting channel with a swirling flow presented excellent sediment sorting to effectively remove the coarse sediment from the high-sediment flow. The minimum efficiency of sediment trapping was 76.9% under different water and sediment incoming conditions. As such, the sediment impact was reduced along the downstream facilities of the channel. Therefore, the sediment characteristics of the desilting channel with a swirling flow can be expected to optimize the incoming flow rate, velocity, and downstream hydraulic conditions. The applicability can also be clarified for the desilting channel with a swirling flow under different water and sediment conditions. The findings can provide a strong reference for the design and application in similar engineering.