# Innovative Hydrogeophysical Approaches as Aids to Assess Hungarian Groundwater Bodies
## 3 Results
### Conventional and Nonconventional Geoelectric Arrays
#### 3.1.2 Fracture and Water-Bearing Zone Detection  
The aim of this study was to detect and characterize fracture zones and fractures since they are profoundly significant in hydrological respect because of their high hydraulic conductivity and water-bearing capacity. Measurements were undertaken a few days after a larger amount of precipitation in the hope that the fractures are still water-saturated, thus electrically conductive. Fracture zone characterization should be easier than that of fractures, but it may also be difficult. In Kadarta, the fracture zone had to be delimited to estimate the water-bearing potential of the area (Figure 6). In spite of that the WS array's data were inverted using both the EarthImager (WS\({}_{1}\)) and 2 DRes-Hu codes (WS\({}_{2}\)), the result was not clear. Although a fault clearly appeared at about 22-23 m in WS\({}_{1}\), no fracture zone seemed to be related to it. A fracture zone appeared at the same time at about the expected position (15-20 m), in  
Figure 5: Study of a series of faults (Section 3.1.1) using different geoelectric arrays: ERT images above a series of faults. Rectangles horizontally delineate the supposed fault fracture zones. a1–3 denotes the anomaly zones. the vicinity of the fault, in the \(\gamma_{113}\) and \(\gamma_{115}\) sections. Its small electrical resistivity must be due to its high water content. Since drilling only a small distance from a narrow fracture zone can drastically reduce the yield of water, it is very important that the \(\gamma_{11n}\) arrays could localize it rather precisely, between 16 m and 18 m. While the WS array displayed only a fault, the \(\gamma_{11n}\) arrays detected and localized rather precisely the water-rich fracture zone. The knowledge of the parameters of individual fractures, such as their position and average distance, is principal in hydrogeological modeling. This was another goal of the Kadarta study. Although ERT is a very good tool for such kind of investigations, there are several problems, which may make difficult the interpretation of data, e.g., the resistivity of the fractures depends on their filling material. Thus, they can be electrically more conductive than the host if they are water-, or clay-filled, but their resistivity is higher than that of the host if they are empty. This problem, however, used to be avoidable if measurements are carried out soon after a rainy period, but it was not the situation in Kadarta. In the Kadarta area, the fractures, which are over a fractured, weathered, porous bedrock, became dry soon after the rain (0-18 m in Figure 7). On the contrary, the fractures in 18-30 m still contained a notable quantity of water in time of the measurements, most likely because the water did not yet leak from these fractures due to the very low permeability of the solid bedrock. Hence, while in 0-18 m, the fractures are electrically resistive, in 18-30 m, they are conductive. The different behavior of the water in different fractures made the interpretation rather difficult in this case. Note that the most significant fractures appeared at the boundaries of the differently weathered block. In rocky terrain, it may be difficult to establish reasonable electrode/rock contact. In the study area, it could be avoided by adding water in the immediate vicinity of the electrodes. The contact was, however, mostly rather good due to the relatively thick layer (0.2-0.6 m) of clay, which covered the bedrock. Contact problems can also be well resolved by attaching sponges soaked in saltwater to the electrodes. Electrodes should be long  
Figure 6: Characterization of a fault and a water-bearing fracture zone by the traditional WS array (inverted by EarthImager code: WS\({}_{1}\), by Res2D-Hu code: WS\({}_{2}\)) and two quasi null arrays (Section 3.1.2). (0.5-1 m) and should be firmly positioned between blocks with maximum contact with the underground [61].