Sediment deposition in water diversion channels threatens the operational safety and water supply reliability of large-scale inter-basin water transfer projects. This study investigates the deposition patterns and sediment reduction strategies for the diversion channel of the Shigu Water Source Project, a key intake hub of the Central Yunnan Water Diversion Project on the Jinsha River. A one-dimensional total-load sediment mathematical model (HELIU-2) was used to simulate deposition volume, particle size distribution, and sediment concentration at the pumping station intake under eight design scenarios spanning high-, medium-, and low-sediment years. Results show that over 95% of the deposited sediment in front of the pumping station is finer than 0.05 mm. Dredging reduces the deposition thickness at the pump intake by 13–25% in high-sediment years, significantly enhancing sediment trapping efficiency and reducing both average and maximum sediment concentrations. Longer diversion channels increase total deposition by 9–13% but reduce intake sediment concentration by 2–5% and decrease local deposition thickness by 27–42%, especially in high-sediment years. These findings provide quantitative support for optimizing desilting basin layout, channel length design, and dredging schedules. The proposed modeling framework and mitigation strategies may provide a reference for other large-scale water diversion systems facing similar sedimentation challenges.

Weird horizontal shapes of branches, in large branching estuaries, often cause significant flood risks and environment-related problems. People usually resort to engineering methods to improve the horizontal shape of the weird branches and solve related issues. The responses of the riverbed evolution of a branching estuary to anthropogenic activity are complicated because of complex estuarine hydrodynamics and sediment transports, especially when the project locates specially (e.g., at estuary outlets). The North Branch of the Yangtze Estuary has a narrow upper reach which is almost orthogonal to the South Branch and has a trumpet-shaped lower reach with a wide outlet. The weird horizontal shape of the North Branch brings significant flood risks to cities along this branch, the shrinkage of its entrance, and other problems. In this study, a regulation of the North Branch, which is launched at Guyuan Sand (GYS) just outside the exit of the North Branch, is taken as an example. The GYS regulation aims to improve the weird horizontal shape of the North Branch by building new layouts of outlets, by which people decrease the flood risk of the surrounding cities. The GYS regulation is studied using a 2D numerical model. The riverbed evolution of the Yangtze Estuary in a typical hydrological year is simulated, while the water/sediment fluxes at cross-sections of branches in the estuary during a spring/neap tide are quantitatively calculated. It is found that the regulation changes the rotational flows near the shore, and further reshapes the estuarine circulations of mass inside the outlets, especially exchanges of water/sediment between different branches. The regulation directly changes the riverbed evolution at the outlet of the North Branch, and meanwhile has significant indirect influences on the riverbed evolution of the entrance of the North Branch. The varying riverbed evolution at the entrance of the North Branch and the varying water/sediment fluxes, under different designs of regulations, are related and analyzed. An essential improvement for the weird horizontal shape of the North Branch by an engineering method is shown to be possible, while the regulation mechanism of the engineering method and the response of estuarine riverbed evolution to the regulation are clarified. This study provides a new insight for improving estuarine branches with weird horizontal shapes, by reshaping the tidal processes and the accompanying sediment transports in a branching estuary.

After the operation of the reservoir, the sediment deposition in the reservoir will raise the bed elevation at the dam site and reduce the reservoir capacity, which will affect the comprehensive benefits of water supply, irrigation and power generation. Taking the Fenghuangshan reservoir in Guangde City, Anhui province as an example, the characteristics of sediment deposition of the Fenghuangshan reservoir was analyzed by using a one-dimensional mathematical model of sediment transport and bed evolution in the reservoir area. Because of the bottom hole, the sediment delivery ratio and out flow sediment concentration gradually increase with the operation time. During the 30 years of operation, the siltation elevation at the dam site increased rapidly, and then the rate of increase began to slow down. In general, the sediment volume into the Fenghuangshan reservoir is not much compared with the reservoir capacity, and the sedimentation is not serious. At the end of 100 years, the reservoir capacity under normal water level and beneficial reservoir capacity are reduced by only 8.79% and 8.24%.

Cyclic steps form under various conditions and their geometry varies, but the physics that controls their geometry is poorly understood. This paper examines the geometry of cyclic steps in the Loess Plateau and explains the intrinsic physics that control their geometry. The data of cyclic steps in gullies from two small basins in the Loess Plateau, China, was collected and we compared this data with existing field and lab datasets. Our field data shows that step length and the ratio of step length to step height decreases with increasing mean channel slope. However, step height itself does not significantly correlate with mean channel slope. Through comparison with other datasets, we find that a less erodible bed develops a smaller ratio of step length to step height, a result confirmed by a theoretical model. We also propose that step length adjusts to dissipate energy, forming a stable system of cyclic steps.