# Groundwater Detection Using the Pseudo-3D Resistivity Method: A History of Case Studies
## 3 Case Studies
### Dam Leakage Detection  
The Xiaojiashan Reservoir survey area is located in the northeastern part of Hunan Province, as shown in Figure 2. It is a medium-sized water conservancy project with comprehensive utilization benefits, such as water supply and flood control. The results of the previous investigation indicate that the dam has potential safety hazards, and that the cause of seepage should be detected and controlled to maintain the integrity and safety of the dam. Due to its location in a karst area, the geological conditions of the Xiaojiashan Reservoir are complex. The structural karsts and fractures are developed, and the dam seepage is serious. Since the numerical modeling results were published [25], here, we directly apply the method to the dam leakage detection. The Xiaojiashan Dam (Figure 3) presents a risk of leakage, so it is necessary to perform a detection. The pseudo-3D resistivity array  
Figure 2: Geographic location map of surveys, (**a**) Xiaojiashan Reservoir leakage survey, (**b**) Zixing groundwater detection survey, (**c**) Huarong groundwater detection survey. is designed as shown in Figure 3. We select the inline pole-dipole device artificial field pseudo\(-\)3D resistivity method in this experiment. The 61 green dots indicate the locations of transmitter electrodes. The 90 purple dots indicate the locations of receiver electrodes. The red rectangle is the investigation area. The distances between the successive receiver electrodes are 10 m. In total, we have acquired 3280 pseudo\(-\)3D resistivity datasets. The pseudo-3D inversion results of the resistivity data are shown in Figure 4a. The results can be described by a 3D resistivity cube. Based on the pseudo-3D electric field experimental results of the Xiaojiashan Reservoir and the cube, we can infer the location of the leakage. Because of the low resistivity, the leak path may show a conductive anomaly in the cube. The channel of the dam is suspected to be the shallow part of the dam, which is marked by a blue arrow. The green part is the low resistivity anomaly, which is separated in Figure 4b. Figure 4: Pseudo\(-\)3D resistivity data inversion results. (**a**) resistivity cube, (**b**) low resistivity path. Figure 3: Pseudo-3D arrays for Xiaojiashan Dam leakage detection. We infer that the dam has a weak layer in the obvious elevation of the current path, and the weak layer does not exhibit a low-resistivity anomaly in the corresponding elevation of profile 1. It is suspected that the pre-stage routing treatment has strengthened some weak layers. It is recommended to collect some data for the specific parts that went through the previous grouting treatment. Figure 5 illustrates the resistivity image by profile (a) 1, (b) 2, and profile (c) 3. Based on the experimental results stereoscopic, the \(-120\)\(--40\)th measurement location in profile 1 and the \(-100\)\(--40\)th measurement location in profile 2 exhibit low resistivity. The anomaly zone is approximately vertical to the dam direction. Figure 5b shows that a low-resistivity anomaly converges within the vicinity of the \(0\)th measurement point in profile 2. The low-resistivity anomaly starts to become shallower near the \(10\)th measurement point of profile 2. Then, this low-resistivity anomaly zone, paralleled with reservoir dam formation, is suspected to be the dam seepage. In Figure 5a, a low resistivity anomaly zone is detected between the location \(-40\) and the \(220\) measurement location. It is also detected on profile 2 (Figure 5b). We infer that the low resistivity anomaly is mainly located in the measurement points segment of profile 1. Figure 5: Sectional view of pseudo\(-3\)D resistivity inversion results of (**a**) profile 1, (**b**) profile 2, and (**c**) profile 3 in the Xiaojiashan Reservoir. In Figure 5b, the shallow part of the \(-\)110-160 th measurement location of profile 2 shows a low resistivity anomaly trend, where the center of the low resistivity anomaly zone is located near the 0-station.