Since large-flow water diversion began in the middle route of the South-to-North Water Diversion Project, inverted siphons have experienced varying degrees of local flow pattern disorder at their inlets and outlets, resulting in a significant decline in hydraulic performance. Taking the Kuhe inverted siphon as a case study, a combination of numerical simulation and on-site testing was used to explore the causes of flow pattern disorder at the outlet of the inverted siphon. Meanwhile, based on the actual engineering situation, the influence of the flow pattern optimization measure of installing a 5D (five times the diameter of the pier) diversion pier at the outlet of the inverted siphon on its hydraulic characteristics was studied. Research findings indicated that before the implementation of flow pattern optimization measures, the Karman vortex street phenomenon was found to occur when water flowed through the piers; the interaction of the vortex streets behind each pier led to flow pattern disorder and affected the flow capacity. After implementation of the flow pattern optimization measures, the diversion piers had a significant inhibitory effect on the formation and development of the Karman vortex street behind the piers under the dispatching and design flow conditions. The flow velocities in each vertical layer were adjusted, with a significant improvement in the flow pattern. The hydraulic loss of the Kuhe inverted siphon was reduced by 11.5 mm, or approximately 7.8%. Under the dispatching flow condition, the water diversion flow of the Kuhe inverted siphon increased by approximately 4.11%. The water diversion capacity of the structure could be effectively enhanced by adding diversion piers to the tails of the piers. This method can be widely applied in similar open-channel long-distance water diversion projects.

In November 2023, surface sediments were collected at 46 sites around the main islands of the Zhoushan Archipelago (Dinghai, Daishan, Qushan, and Shengsi) in the East China Sea. The concentrations of Cu, Zn, Cr, Pb, Cd, Hg, and As were determined, together with sediment TOC and Eh. Pollution and ecological risks were evaluated using the single-factor index (Pi), Nemerow pollution index (PN), and Hakanson’s potential ecological risk index (RI). Source apportionment was investigated using FA–PC and EPA PMF 5.0. Mean concentrations (mg/kg) were Zn 77.58, Cr 70.08, Cu 28.44, Pb 18.92, As 9.40, Cd 0.09, and Hg 0.073, with higher levels generally observed near Dinghai, Daishan, and Shengsi. The overall risk was low, whereas Cd and Hg contributed disproportionately to RI. FA–PC suggested two major source groups, and PMF resolved three factors related to (i) agriculture/aquaculture (As), (ii) industrial and domestic effluents (Hg), and (iii) port and ship-related activities (Cd, Cu, Cr, Pb, Zn). The results support targeted management focusing on Cd, Hg, Cu, and As in identified hotspots.