Effect of water-retaining weir height on the discharge capacity of a segmented low-pressure water conveyance project

To clarify how water-retaining weir (WRW) height affects the discharge capacity of a segmented low-pressure water conveyance project, this study combined physical model tests with numerical simulations for a representative box culvert–weir well–WRW segment under different WRW heights, with a focus on the effects of WRW height on the flow-field characteristics and water-level distribution in the weir well, as well as on the discharge capacity of the representative segment, under free-weir-flow, submerged-weir-flow, and highly-submerged-weir-flow conditions. The numerical model agreed well with the physical model test results. Reducing the WRW height shifts the main flow region downward, weakens the flow-blocking effect of the WRW, increases the flow velocity at the breast-wall section, and redistributes the upstream and downstream water levels in the weir well. These hydraulic changes improve the discharge capacity of the water-conveyance box culvert in the representative segment. As the WRW height decreases, the discharge through the water-conveyance box culvert gradually increases; however, as the relative submergence increases, the sensitivity of discharge capacity to WRW-height variation decreases markedly. The results can provide a reference for the design and operation of similar water conveyance projects.