## 4 Three-Dimensional Transient Seepage of the Hydrogeological Models
### Transient seepage Analysis  
Assuming that the inverted model produced results that were practical for the engineering, the hydrogeological model was used to predict the influence of normal seepage conditions on the changes in the groundwater seepage field during the excavation of the tailwater tunnel using a three-dimensional transient numerical simulation. The range of the influence of the tunnel excavation on groundwater was analyzed qualitatively, and the distance over which there were changes in the pore water pressure head because of the tunnel excavation was quantified and analyzed. The depleted well points where the villagers were experiencing drinking water shortages were added to the model and simulated. Well points SJ96, SJ141, SJ146, and SJ202 were included in this analysis. Information on the distance between the well points and the axis of the tailwater tunnel is given in Table 3. For each of these wells, the patterns and changes in the water levels for the five seepage control schemes were analyzed. The variations in the water level at well points SJ96, SJ141, SJ146, and SJ202 for the five seepage control schemes are shown in Figure 11. As shown in Figure 11, the groundwater levels in well points SJ96, SJ146, and SJ202 were 0.054, 0.039, and 0.025 m, respectively. Figure 11 also shows that the groundwater levels were affected by the excavation of the tunnel, and the levels decreased as the distance from the tunnel site increased, and the rate of the decrease in the water level slowed as the distance from the tunnel increased. Figure 11,c,e,g,i show that the water level decreased as the maximum transient flow increased. The water levels in well point SJ202 decreased by 0.025, 0.029, 0.031, 0.032, and 0.034 m for the five seepage control schemes. Figure 11: _Cont._ \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Well** & **Location** & \begin{tabular}{c} **Distance from** \\ **Tunnel Axis (m)** \\ \end{tabular} & \
\begin{tabular}{c} **Wellhead** \\ **Elevation (m)** \\ \end{tabular} &
\begin{tabular}{c} **Depth of Well (m)** \\ \end{tabular} \\ \hline SJ96 & Yangshuwan Village, south of the tunnel & 750 & 113.0937 & 6.9 \\ SJ97 & Yangshuwan Village, south of the tunnel & 790 & 110.3317 & 7.9 \\ SJ141 & Qiandawan village, south of the tunnel & 101 & 114.6467 & 15 \\ SJ142 & Qiandawan village, south of the tunnel & 105 & 115.8357 & 11 \\ SJ146 & Tulou Village, south of the tunnel & 1150 & 111.4187 & 8.8 \\ SJ202 & Yangmingao village, north of the tunnel & 1000 & 125.3427 & 7 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Drained civilian Wells. Figure 11: Changes in the water level for the different water inflow conditions. ((**a**) and (**b**) are changes in water level of the maximum water inflow of 200 m\({}^{3}\)/d, (**c**) and (**d**) are the variation of water level for the maximum water inflow of 400 m\({}^{3}\)/d, (**e**) and (**f**) are the changes in water level when the maximum inflow is 600 m\({}^{3}\)/d, (**g**) and (**h**) are the changes of water level when the maximum water inflow is 800 m\({}^{3}\)/d, (**i**) and (**j**) are the changes of water level when the maximum water inflow is 1000 m\({}^{3}\)/d). The water level in well point SJ141 first decreased and then increased as the tunnel excavation progressed, as shown in Figure 11b. Because of the excavation of the tunnel, a water inrush channel formed, the groundwater circulation system was disrupted, the groundwater seepage to the tunnel accumulated at a certain distance from the tunnel excavation, and the water level of the well point SJ141 decreased. As the distance from the tunnel excavation increased, the water inflow also increased, and the area of groundwater affected also increased. There was a large range in the distance of the groundwater seepage flows at places close to the tunnel (such as well point SJ141), resulting in temporary increases in the water level at well point SJ141.