# Groundwater Detection Using the Pseudo-3D Resistivity Method: A History of Case Studies
## 1 Introduction  
With the rapid growth of population, urbanization, and industrialization, the sustainable utilization of water becomes more and more important. Any urbanization development is directly or indirectly related to the use of water. For any development activity, surface water and groundwater sources are the main components. The detection and exploitation of groundwater is of great practical significance to a city's populace. However, groundwater, unlike surface water, can hardly be intuitively observed. Many zones with groundwater are associated with cracks and fractured media. Thus, groundwater exploration in hard rock terrain is a very challenging and arduous task. We have to use some special methods to detect groundwater. The geophysics method is one kind of non-destructive detection method that was widely used in recent years [1]. Some of the characteristics of this method are: easy measurement, high work efficiency, accurate detection results, and a large research area [2]. Researchers have successfully applied geophysical methods to detecting groundwater reservoirs [3]. Some examples are: electrical resistivity sounding [4], the electromagnetic method [5], and ground-penetrating radar (GPR) [6]. With the advantages of non-destructive detection, geophysical methods can be used to not only detect groundwater, but also to detect dam leakage. The most common hydro-geological problem with most dams is bedrock and lake seepage, especially fill dams built on faults and deformed structures [7]. Therefore, it is particularly important to detect and measure the dam leakage in advance to avoid the potential loss caused by the leakage of the reservoir. In order to avoid drilling or other penetrating investigations, geophysical methods with non-destructive testing are usually chosen for dam leakage detection andmonitoring. Dam leakage of groundwater is a major safety issue for dam failure. There are successful case studies published on using different methods [8], for instance, electrical methods [9; 10; 11; 12], ground-penetrating radar (GPR) [13], seismic [14; 15], and electromagnetic methods [16]. The electrical method is a useful tool for dam leakage detection and groundwater detection [17; 18]. Researchers also introduced the DC resistivity method [19; 20]. DC electrical resistivity imaging (ERI) is used to locate and characterize the defaults in early research [21]. [PERSON] employed this classical 2D ERI data acquisition system with external 3D information in the data [12]. [PERSON] studied the capability of the DC approach to map the dam leakage resistivity 3D distribution [22]. The research of [PERSON] et al. is the same for groundwater exploration, which shows that groundwater will lower the resistivity value, and that silt will also decrease the resistivity value more than the effect of groundwater [17]. Due to the difference of the 3D space distribution of the embankment geometry, [PERSON] and [PERSON] studied the 3D effects on the 2D electrical resistivity tomography data inversion [23]. [PERSON] and [PERSON] conducted a 2D electrical resistivity tomography survey in the Harrat Khaybar volcanic field, northeast of Al Madinah AlMunawwarah, Saudi Arabia, to assess the presence of groundwater resources [24]. The groundwater and dam detection can both be easily achieved by 2D inline geometry. However, 3D resistivity imaging can provide more information about the groundwater and dam leakage [25]. As a traditional geophysical method, dual-frequency resistivity is widely applied in mineral exploration, groundwater exploration, and so on. Although some work on dam investigation applications and groundwater detections was carried out in the past, neither 2D nor conventional 3D electrical methods were successful in addressing the actual needs of groundwater and dam leakage detection [22].