## 1 Introduction  
With the rapid economic development in China, the energy demand, especially for clean energy such as water, is continuing to increase. Over the last two decades, 27 pumped storage power stations, which are special power source that have flexible operation modes and multiple functions, have been completed, with a total installed capacity of 21.83 GW [1]. However, during the construction of these hydropower stations, it is inevitable to face the hydrogeological problems of groundwater inflow [2] and its associated environment impacts [3, 4], which may lead to casualties [5], tunnel instabilities [6], water desiccation [3], and environmental degradation [7]. Therefore, the estimation of groundwater inflow and the assessment of environment impacts are necessary for the design and construction of hydraulic projects [3].  
Analytical methods play an important role in the first quick estimation of water inflow from the mirror image method [8, 9, 10], the well theory [11, 12], to the complex variable method [13, 14, 15]. Yet, the analytical formulas which cannot take into account the complex geological conditions may tend to over/underestimate the groundwater inflow rate. Compared with analytical formulas, numerical methods have been developed with the advancing of faster computers, which can be applied in more complicated scenarios with more reasonable results [3]. In addition, empirical methods like SGR (Site Groundwater Rating) [16], TIC (Tunnel Inflow Classification) [17], and GRS (Groundwater Seepage Rate) [18] have been presented based on lots of engineering cases in recent years, which can qualitatively and quantitatively calculate the groundwater inflow rates of underground caverns or tunnels. Consequently, a comparative study on the evaluation of groundwater inflow to tunnels or caverns is crucial for designing drainage systems [19].  
Many aspects of environmental impacts (i.e., hydrochemical evolution [20], reservoir immersion and leakage [12; 21], climate change [22; 23], and ecosystem impacts [24]) have been reported in the existing literature considering the representations of surface water more than groundwater. However, for the tunneling or hydraulic projects, especially those with complex drainage systems, the drainage effects, including the water table drawdown and depression cone caused by groundwater inflow, have not received enough attention. Actually, the difficulty involved in solving these drainage problems is to estimate the highly nonlinear free surface and the singular seepage points, which can be generally obtained by numerical methods (e.g., the residual flow method [25], the initial flow method [26], the adjusting permeability method [27], the variational inequality method [28]). [PERSON] et al. [29] proposed a new variational inequality formulation of Signorini's type combining with the finite element method (FEM), which can theoretically overcome the singularity at the seepage points and properly proscribe the boundary conditions compared with other numerical methods. Hence, the drainage galleries or underground caverns with relatively large sizes, regular shapes, and extensions can generally be explicitly modeled in the FEM and be properly addressed using the new numerical method.  
The objectives of this paper are to (1) compare the different methods used for the evaluation of groundwater inflow into the underground powerhouse of Jinzhai pumped storage power station, and (2) assess the drainage effect caused by tunnel inflow during the construction. To accomplish this task, the engineering geological and hydrogeological conditions of the site are described in Section 2. Then, various methods associated with the specific application conditions are reviewed, and a comparison is made in Section 3. Finally, the drainage effects including water table drawdown, water pressure redistribution, and hydraulic gradient are analyzed in Section 4. This case study can provide references for the construction of other hydraulic projects.