## 5 Conclusions  
The evaluation of groundwater inflow and associated drainage effects during the construction of hydraulic projects is of great concern. In this study, a comparative study on the estimation of groundwater inflow into the underground powerhouse of the JPSPS was proposed by using three kinds of methods (i.e., analytical, empirical, and numerical methods). Furthermore, the drainage effects, including water table drawdown, water pressure redistribution, and hydraulic gradient were evaluated. The main conclusions that can be drawn from this study are as follows:  
1. The analytical methods considering a stable water table may mostly overestimate the water inflow rates of the underground powerhouse, with an approximate value of 3000 m\({}^{3}\)/d. Conversely, the analytical results considering the drainage effect show a decent fit with the numerical solution in the excavation condition. Based on the refined numerical simulation of seepage control measures in the operation condition, the water inflow rate is significantly reduced to 104.47 m\({}^{3}\)/d. Using the SGR method, the underground powerhouse is in \"_Low Risk_\" class, with a SGR coefficient of 292.86. 2. The seepage-free surface intersects precisely on the boundaries of the main and auxiliary powerhouse and tailrace gate chamber, which indicates that the groundwater above these cavern roofs is completely drained. The drainage structures combined with waterproof curtain can reduce the water inflow rates, but cause an increase in the water table drawdown and depression cone. A comparison between analytical and numerical methods and monitoring data of water table drawdown can not only highlight the drainage effect but also show the complexity of the study site. 3. The underground caverns associated with drainage structures significantly change the pore water pressure distribution and hydraulic gradient. The seepage control measures including drainage holes and tunnels and waterproof curtain prevent groundwater from entering caverns, resulting in a decrease in hydraulic head and water pressure. However, the high relative permeability brings an increase in the inflow rates and hydraulic gradient within the faults (F\({}_{318}\), f\({}_{317}\)). Hence, it is necessary to pay attention to the water inrush in faults during excavation. 4. Although the capabilities of various methods for tunnel inflow have been effectively identified and the drainage effects caused by cavern excavation have been comprehensively evaluated, the framework proposed in this study has some limitations, especially with homogeneous isotropic media, 2D numerical modeling, steady-state Dracy flow, and simplifying assumptions of analytical formulas. Therefore, the future research advances are necessary to focus on the interactive effects of heterogeneous anisotropy of fractured rock, faults, and seepage control measures on tunnel drainage using a three-dimensional transient numerical simulation. Figure 13: Hydraulic gradient of seepage field in numerical Case 2, and the blue arrow represents the groundwater flow direction. **Author Contributions:** Conceptualization, [PERSON] ([PERSON]) and Z.Z. ; methodology, [PERSON] ([PERSON]); software, Z.Z. ; validation, [PERSON] ([PERSON]) and Z.Z. ; formal analysis, [PERSON] ([PERSON]) and Z.Z. ; investigation, [PERSON] ([PERSON]); resources, Z.Z. ; writing--original draft preparation, [PERSON] ([PERSON]); writing--review and editing, [PERSON] ([PERSON]) and H.W. ; visualization, [PERSON] ([PERSON]); supervision, [PERSON] ([PERSON]); project administration, H.W. and B.C. ; funding acquisition, [PERSON] ([PERSON]). All authors have read and agreed to the published version of the manuscript. **Funding:** This research was funded by the Postdoctoral Fund Project of Shanghai Investigation, Design & Research Institute Co., Ltd. (SIDRI), grant number 2024 JC(831)-001, and the National Natural Science Foundation of China, grant number 91747204.