## 4 Discussion
Accurate mapping of the boundaries of geological strata is crucial for assessing the foundation conditions of a dam (which showed the issue concerning Krasnowice and Szalejow Gorny reservoirs), as the different rock formations exhibit different geotechnical and hydrogeological properties. Cretaceous limestones and marks can differ in cohesion, porosity or susceptibility to erosion, among other things, so that inaccurate determination of their extent can lead to misinterpretation of the stability of the foundation [39]. Errors in interpolating geological data between boreholes presents another challenge--with typical inter-borehole distances of 10-50 m, the geological profile between points is unknown and must be inferred from experience or model assumptions [40]. The limited amount of data results in a high degree of uncertainty in the representation of geological strata, which ultimately makes design decisions difficult. Even with many boreholes, the degree of uncertainty persists and the consequences of incorrect predictions can be catastrophic. In doing so, it should be emphasised that the boundaries of geological layers generally have the highest uncertainty in models [41]. For this reason, key decisions--such as the foundation depth of the dam body--must be based on the most accurate, robust ground model possible, taking this risk into account. The compiled results indicate that the initial decision to construct the dam body directly on the roof of the Cretaceous layer and to use the profile determined using boreholes along the dam axis as a determinant of soil replacement depth was a controversial one. The original investigations indicated that the roof of the marl layer might have insufficient bearing capacity, requiring additional deepening of the embankment body until reaching a layer with the appropriate parameters, which was confirmed in situ. The follow-up investigations further revealed a greater depth of the marl layer than initially expected in the eastern section of the dam. It can thus be concluded that a higher density of boreholes drilled directly in the area of the dam body would have allowed for a more accurate estimation of the required embankment foundation depth and, hence, a more precise calculation of the soil volume needed to be extracted from the deposits. Many geotechnical problems similar to those identified in the present case study have also been documented in other regions worldwide. In the Alpine foreland (e.g., the Kauretal Valley, Austria), significant variability of glacifluvial deposits has been observed even over short distances, complicating the interpretation of borehole data and potentially necessitating unforeseen design adjustments [42]. In karst areas (e.g., Montejaque, Spain), an extensive network of karst voids was found to prevent the reservoir from being filled, despite prior investigations and grouting works [43]. A global analysis of leakage in karst reservoirs (e.g., in China) demonstrated the need for costly remedial measures or permanent sealing interventions [44]. Recent research indicates that combining borehole investigations with geophysical techniques enables more effective identification of potential leakage zones. In recent years, electrical resistivity tomography (ERT) has been increasingly employed to provide detailed mapping of horizontal and vertical distributions of zones with varying electrical conductivity, indicative of groundwater presence, karst voids, or loosened seepage zones. Another example is the application of audio-frequency magnetotellurics (AMT), which was used, for instance, to investigate the Yibasan reservoir in Yunnan Province, China, allowing the identification of 40-60 m wide low-resistivity zones interpreted as karst conduits and leakage pathways [45]. The different survey technology involving the exploration of deposits for the construction of the Krasnowice and Szalejow Gorny dams was associated with significant differences in results. The boreholes led to the extraction of soil cores with a diameter of 8 cm [24].