## 5 Conclusions  
This study primarily focused on the pressure pipeline system of the New Longkou Hydropower Station in the Kuitun River Diversion Project, utilizing the water hammer characteristic line method for calculations. The water hammer pressure and its variations were analyzed under different valve closing times and two-stage closure strategies while also considering potential load rejection scenarios. Furthermore, CFD simulations were employed to assess the impact of other factors on the flow patterns at the upstream end of the pipeline. Through a combination of two-dimensional and three-dimensional simulation methods, this study not only analyzed the overall pipeline water hammer but also investigated the changes in flow patterns at the pipeline valve locations. The main conclusions are as follows. During the first-stage linear valve closure, the water hammer pressure increased progressively along the pipeline, with larger fluctuations occurring closer to the terminal units. Shorter valve closure times resulted in higher peak water hammer pressures, whereas extending the closure time effectively mitigated the negative pressure in the pipeline. Extending the valve closure time reduced the peak water hammer pressure at the valve terminal and decreased the frequency of peak occurrences. For the same closure time, the smaller units experienced more frequent pressure fluctuations at the valve terminal. Compared with the first-stage valve closure, the two-stage closure increased the water hammer pressure by 8% to 14.1%, potentially causing flow interruption, negative pressure, and exceeding the pipeline pressure limit. Based on the load-shedding conditions, it is recommended to implement a linear valve closure time greater than 9 s or to use a strategy of 60% fast closure and 40% slow closure. The distance between the branch pipes at the Xinlongkou Hydropower Station had minimal impact on the maximum water hammer pressure, whereas the number of valves significantly influenced the pressure. The primary factors affecting the water hammer pressure, in order of significance, were valve closure time, valve quantity, valve diameter, and branch pipe distance. The combination of two-dimensional and three-dimensional water hammer calculations offers advantages of both accuracy and efficiency. Compared with traditional one-dimensional or two-dimensional methods, it provides a more intuitive representation of the water hammer phenomenon within a pipeline, facilitating the analysis of flow field characteristics and the optimization of localized protection designs. This approach provides more comprehensive and reliable technical support for water hammer protection. The combination of two-dimensional and three-dimensional water hammer calculation methods efficiently identified the key nodes. By using two-dimensional calculations for rapid system-wide simulation, followed by three-dimensional analysis for a detailed evaluation of high-risk areas, this approach allows for a comprehensive assessment of local flow fields and pressure distributions. This method balances computational efficiency with accuracy, optimizes protective designs, and enhances cost-effectiveness. It is applicable to complex conditions such as multibranch pipelines and pump station water transport, providing a reliable scientific tool for similar projects and contributing to improved design precision and operational safety. It is worth noting that issues such as mutual coupling effects between valves in complex hydraulic circuit systems, fluid-structure interactions (FSI), and hydraulic vibrations require further in-depth investigation. In the future, we plan to conduct more comprehensive studies on these influencing factors by expanding the numerical simulation methods, for example, employing more advanced turbulence models and FSI algorithms, and performing field experiments for validation. In addition, we propose more systematic water hammer protection and control strategies tailored to water transport projects of varyingscales and configurations.