The pressure characteristics of long-distance water pipelines during hydraulic transient processes are crucial for ensuring the safe, stable, and long-term operation of water transfer projects. This paper establishes a one-dimensional mathematical model based on sections of the Yinjiangjihuai long-distance water diversion project in China. The water supply requirements of the pipelines are categorized into two replenishment modes as follows: gravity supply and pump-pressurized water supply. The opening and closing strategies of the water pipelines under different flow conditions are simulated and analyzed to explore the hydraulic transient processes under various water supply modes. The transient variations of key hydraulic parameters during valve closure are clarified. Simulation results indicate that the water pipeline design is reasonable, meeting the water supply demands at relatively low Manning values and that it has the capability for long-term supply. Due to the excessive head provided by the pumps, pump-pressurized water supply and gravity supply modes cannot operate simultaneously. Under gravity supply mode, the minimum pressure in the downstream pipeline is relatively higher overall, while the maximum pressure in the upstream pipeline is relatively lower overall. In the pump-pressurized water supply mode, the safety and stability of the water supply can be ensured by adjusting the closing time of individual pumps and the interval time between adjacent pumps. The research findings provide technical guidance and scientific basis for the construction of national water networks and water transfer projects.

Rapid filling of urban drainage pipelines during intense rainfall can compress entrapped air and trigger pressure surges or geysering when air release through manhole-cover openings is restricted. Unlike studies focusing on simplified pipes or isolated shafts, this work examines the coupled air–water response of a prototype-scale drainage section with drop structures, branch inflows, variable-diameter inverted siphons, multiple shafts, and restricted manhole-cover venting. A three-dimensional unsteady air–water two-phase model was established and applied to nine two-stage inflow scenarios after validation against published rapid-filling pressure data. The results show that hydraulic slugs segmented the continuous crown air layer into localized air pockets and produced a high-pressure concentration zone upstream of the downstream diameter change, with a maximum shaft-top pressure of 29.2 kPa under the representative high-flow condition. In local shafts, insufficient venting through small openings, bottom water sealing, and continuous air supply jointly induced delayed geysering cycles characterized by pressure accumulation, breakthrough, relief, and re-accumulation, with a period of 110–120 s and peak pressures of 19–21 kPa. The second-stage rapid-filling flow rate dominated downstream peak pressures; when it increased from 9 to 11 m³/s, the peak pressure at a representative downstream shaft rose from 16 to 34 kPa. These findings clarify the mechanisms of high-pressure concentration and delayed geysering under restricted venting and support the identification of pressure-sensitive nodes in complex drainage networks.

The study focuses on a key component of the Yangtze–Huaihe River Diversion Project—the Qiliqiao to Xincheng water supply pipeline section, which includes a megascale inverted siphon structure. A one‐dimensional mathematical model is developed to simulate water hammer phenomena in transmission pipelines containing the large siphon. A comparative analysis is conducted to evaluate the protective effects of linear and nonlinear valve closure strategies. The optimal valve closure scheme is explored by parameterizing the valve closing duration and buffering time. The impact of air valves installed near the inverted siphon during hydraulic transition processes is examined, and the transient variations of key hydraulic parameters during the entire valve closure operation are systematically characterized. Under long‐term operational conditions with Manning’s coefficient degradation, the designed pipeline maintains a hydraulic head surplus of 7.34 m, fully meeting long‐distance water supply requirements. Air valves effectively reduce the peak pressure magnitude by 80%. Under linear valve closure conditions, only the high‐elevation air valves exhibit significant exhaust behavior. In contrast, nonlinear closure strategies reduce the minimum internal pressure of the pipeline and suppress vaporization, thereby reducing the air valve discharge volume. Finally, the study identifies an optimal time coordination scheme by adjusting the closure timing of individual pumps and the interval between adjacent pump shutdowns.

Manhole shafts in urban drainage systems are prone to accumulating trapped air pockets during intense rainfall, which can lead to sudden bounce of hinged covers and pose significant near-field risks. However, threshold criteria at the prototype scale remain unavailable. To obtain quantitative evidence of cover bounce under full-scale conditions and to clarify the effects of counterweight, dual-shaft coupling, and pressure–displacement phase lag, a series of experiments have been conducted on a prototype platform consisting of two shafts with hinged covers. Tests have been repeated under various counterweight conditions ranging from 0 to 30 kg. Pressure data from multiple transducers and high-speed video recordings have been synchronously acquired, filtered, and temporally aligned. Based on these, the critical overpressure at initial lift-off was identified, and oscillation characteristics and coupling effects have been analyzed. The critical overpressure was found to increase monotonically with added counterweight. When the counterweight was large, the system transitioned into a decaying response, with negligible subsequent bounce. The single-peak “rise–fall” pattern observed in single-shaft conditions no longer appeared when both covers lifted simultaneously. Notably, the critical overpressure did not coincide with the pressure peak, and a significant phase lag was observed between the pressure maximum and the moment of maximum displacement. These findings provide actionable support for the identification, modeling, and rapid mitigation of manhole cover bounce risks in urban drainage systems.

In one-dimensional (1D) transient simulations of unpressurized drainage networks, confluence junctions are commonly represented using static hydraulic coefficients, which cannot adequately capture their dynamic hydrodynamic behavior. To address this limitation, three-dimensional (3D) simulations validated against experiments were conducted to investigate the flow physics and hydraulic characteristics of circular pipe confluences. The results demonstrate that, beyond the junction angle θ and the discharge ratio q*, the filling ratio y* plays an important role in governing the flow structure. As y* increases, it non-linearly modifies the cross-sectional aspect ratio and increases the submergence of the branch inflow, driving a transition from smooth merging to vigorous rolling with intensified turbulent kinetic energy dissipation. Based on these flow physics insights, a dynamic 1D control volume confluence branch junction model was developed, where the momentum correction and localized head-loss coefficients vary with the transient flow. To complete the model, a database of 150 3D simulations was established, and the control volume boundaries were identified at 0.2, 0.9, and 1.4 pipe diameters upstream, branch, and downstream sections, respectively. Formulas for the quasi-dynamic hydraulic coefficients were then derived as functions of θ, q*, and y*. By incorporating these formulas, the 1D model demonstrated high accuracy for transient flow simulation: reducing the maximum dynamic time warping water-depth alignment error by 68.69% and the peak water-depth relative error from 5% to 0.1% in their respective cases. These results demonstrate that incorporating dynamic junction characteristics enables the proposed 1D model to more accurately represent confluence hydrodynamics in unpressurized circular pipe systems.