Water and sediment characteristics in a trapezoidal desilting channel with a swirling flow generator

This study aims to determine the water and sediment characteristics of the trapezoidal desilting channel with a swirling flow generator (TDCSFG) under different water and sediment conditions. The model test was also adopted to verify the water and sediment movement and sediment discharge of TDCSFG. Different conditions of water and sediment were then selected, such as incoming flow rates, mass of added sediment, median particle size of inflow sediment, and inlet flow velocities, as well as its split ratio. Finally, a systematic investigation was made to clarify the distribution of water consumption, sediment trapping efficiency, and residual sediment efficiency. The results show that there was a small water consumption for the sediment discharge, indicating the remarkable effect of desilting. Furthermore, the sediment carrying capacity of water flow increased significantly, as the flow rate or inlet flow velocities increased. The amount of suspended-load sediment increased, whereas, the bed-load sediment decreased in the bottom water layer. The sediment trapping efficiency of TDCSFG decreased, whereas, the residual sediment efficiency increased, indicating the outstanding influence on the sediment discharge. Once the incoming flow rates increased from 30 to 90 m3/h or the inlet flow velocities increased from 0.57 to 1.60m/s under experimental conditions, the sediment trapping efficiency decreased from 92.97% to 76.16% and 92.97% to 79.77%, respectively, where the variation ranges of sediment interception rate were 16.81% and 13.20% respectively; the maximum residual sediment efficiency increased from 5.28% to 21.38% and 5.28% to 18.77%, respectively, where the variation ranges of residual sediment efficiency were 16.10% and 13.49%, respectively. The most influence was concentrated mainly in the sediment with the particle size range of >0.075~0.315 mm. Once the mass of added sediment increased from 300 to 700g or the median particle size of inflow sediment increased from 0.315 to 1.250 mm, there was an increase in the content of particle-size sediment in the lower flow, and the bed-load sediment. The sediment-carrying force generated by the flow only carried the part of small-size sediment into the downstream channel. The sediment trapping efficiency of TDCSFG increased, whereas, the residual sediment efficiency decreased. Specifically, the sediment trapping efficiency increased from 92.97% to 95.27% and 89.53% to 95.83%, respectively, where the variation ranges of the sediment interception rate were only 2.63% and 6.33%, respectively. The maximum residual sediment efficiency decreased from 5.28% to 2.85% and 8.64% to 3.59%, respectively, where the variation ranges of residual sediment efficiency were 2.43% and 5.05%, respectively. As such, the mass of added sediment and median particle size of inflow sediment shared little influence on the sediment discharge of TDCSFG, where the particle size range of > 0.160~1.250 mm was discharged. The great sediment discharge of TDCSFG was found under different water and sediment conditions. The minimum sediment trapping efficiency was 76.16%, and the sediment trapping efficiency was no less than 94.88% for the sediment particles with a particle size >0.600~3.000 mm. Therefore, TDCSFG had effectively discharged the harmful sediment in the channel. Among them, the split ratio was reduced by 6.43 ~ 16.66% under the similar sediment trapping efficiency and reduced, compared with the rectangular cross-section channel at the same flow rate or the same median particle size of inflow sand. The sediment accumulation was improved after the increasing inclination angle in the closed end of the sediment transport pipe. There was no sediment accumulation at the bottom of the upstream and downstream channels, swirling flow generator, and in the sediment transport pipe, indicating the efficient utilization of water and sediment resources. There was also the high suitability and high efficiency of the trapezoidal desilting channel with a swirling flow generator. The finding can also provide a strong reference for future applications in engineering.