## 4 Results and Discussion
### Groundwater Level Analysis of Dam Site during the Reservoir Operation  
During the reservoir operation, the seepage control and drainage measures for underground buildings were used in the dam site. Drainage holes have been installed in an underground powerhouse. Impervious curtain was arranged in the dam foundation and both banks and extended to the position of karst pipes. It mainly discusses the variable of groundwater flow field of karst pipeline impervious curtain under normal and invalid conditions. The normal impounded level of the reservoir is 1030 m. In addition, the water level behind the dam is 965.47 m. Contour maps of groundwater level for underground powerhouse and karst pipes are shown in Figure 9. It can be seen that contour shape, trend, and distribution of groundwater level accurately reflected the characteristics of seepage control, drainage measures, and boundary conditions in corresponding areas (Figure 9a). Owing to the action of anti-seepage treatment and drainage measures, the seepage control effect was obvious. The general trend of groundwater level was convergence from upstream and downstream to an underground powerhouse area. The groundwater level fell obviously near it. It can be seen from Figure 9b,c that the groundwater level decreased obviously after passing through the curtain and drainage of the underground powerhouse. Where there was a curtain, the water level isoline was relatively close, which reflected the water-blocking effect of the impervious curtain. There occurred regular bending of the groundwater level in the karst pipe area. In addition, the bending place was the direction of the karst pipe. The groundwater level in the pipe decreased obviously after passing through the impervious curtain.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{
\begin{tabular}{c} **Zones of Vertical** \\ **Direction** \\ \end{tabular} } & \multicolumn{6}{c}{**Zones of Horizontal Direction**} \\ \cline{2-9}  & \multicolumn{2}{c}{**Strong Permeable Zone**} & \multicolumn{2}{c}{**Weak Permeable Zone**} & \multicolumn{2}{c}{**Slight Permeable Zone**} \\ \cline{2-9}  & \(K_{x}\) & \(K_{y}\) & \(K_{z}\) & \(K_{x}\) & \(K_{y}\) & \(K_{z}\) & \(K_{x}\) & \(K_{y}\) & \(K_{z}\) \\ \hline Strong weathering zone & 0.49 & 0.49 & 0.05 & 0.39 & 0.38 & 0.04 & 0.28 & 0.29 & 0.03 \\ Weak weathering zone & 0.39 & 0.38 & 0.04 & 0.29 & 0.30 & 0.03 & 0.15 & 0.15 & 0.02 \\ Slight weathering zone & 0.28 & 0.28 & 0.03 & 0.11 & 0.10 & 0.01 & 0.03 & 0.02 & 0.003 \\ \hline \hline \end{tabular}
\end{table}
Table 7: Permeability coefficients of fracture- karst media by inversion method (m/d).  
Figure 8: Contour map of groundwater level in the study area with five karst pipes.  
Groundwater in the study area was mainly discharged from the mountain bodies on both banks to the Mabie River. However, after reservoir impoundment, groundwater was mainly discharged from the upper reservoir to the lower reaches of the dam and the powerhouse through the two banks and dam foundation. The groundwater level of the powerhouse has decreased by about 2-5 m. Water conveyance pipeline has risen by 10-20 m and 15-25 m for mountainous bodies on both banks. Therefore, the natural flow field of groundwater has been greatly changed by the water conservancy project.