## 2 Materials and Methods
### Krasnowice and Szalejow Gorny Reservoirs  
These reservoirs are described in one and the same subsection, considering that they face identical issues related to the identification of differing geological conditions. The Krasnowice reservoir on the Duna stream has a maximum capacity of 1.9 million m\({}^{3}\), with a floodplain area of 44.12 ha. The Szalejow Gorny reservoir on the Bystrzyca Dusznicka river has a maximum capacity of 10.67 million m\({}^{3}\), with a floodplain area of 118.7 ha. In both cases, geological investigations at the planning stage were carried out using boreholes only, completely ignoring other geophysical technologies. The results revealed the possibility of using the soils in the reservoir basin (in particular, cohesive soils) for the construction of the dam body. For Szalejow Gorny, specific soil layers designated for this purpose were identified, with their parameters listed in Table 2. With respect to Krasnowice, all that was defined was the necessity to use cohesive soils compacted to a density index of \(\geq\)0.95 [24]. Example values of the cohesive soil parameters identified in the Krasnowice reservoir basin were added to Table 2 [25]. Figure 4: Locations of the boreholes and route of the anti-filtration screen. The dams of both reservoirs were designed to be founded on the roof of the Cretaceous layer, particularly on rock formations (marl or sandstone). At the construction stage, it was noted that the load-bearing soils in many areas did not reach the elevation designated as the soil replacement line, with locally significant deepening. This circumstance resulted in the need to conduct follow-up investigations of the subsoil beneath the dam body. In addition, given the potential increase in its volume (due to the deepening of the foundation), the soil deposits in the reservoir basin were also investigated to verify their actual quantity and availability. The locations of the original boreholes and the test excavations and boreholes are shown in Figures 6 and 7. The boreholes and excavations on the deposits used in the further analyses are labelled with the letters P and R, respectively. Similarly, the original and test boreholes beneath the dam body are labelled with the letters D and C. In order to accurately depict the geological conditions of the area of both dams-cross sections through the valleys in which they were formed have been added in Supplementary Figures S1 and S2 [24; 25]. A photograph representing the location of the deposits and the nature of the construction area is included in Figure 8. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Description and Location** & **Bulk Density** & **Plasticity Index** & **Angle of Internal** & **Cohesion** \\  & \(\rho\) [kg/m\({}^{3}\)] & **I\({}_{\text{L}}\) [-]** & **Friction \(\Phi\) [\({}^{\circ}\)]** & **C [kPa]** \\ \hline Szalejów—A & 2.082 & 0.05 & 11.0 & 30.0 \\ Szalejów—B & 2.001 & 0.35 & 8.0 & 20.0 \\ Krosnowice—C & 2.032 & 0.084 & 17.0 & 18.9 \\ \hline \hline \end{tabular}  
* A—silty Ioams, silty Ioams with sand, and sandy Ioams with fragments of crystalline rocks; B—silty Ioams with sand, silty Ioams and sandy Ioams with rock fragments and loam with sandstone cobbles; C—sandy Ioams, and sandy and silty Ioams in a hard-plastic state.  
\end{table} 
Table 2: Parameters of the soil originally planned for the dam of the Szalejów Góny and Krosnowice reservoirs [24; 25]. Figure 5: Design solution for the watertight barrier of the Roztoki Bystrzyckie reservoir. Figure 6: Location of geological investigations (original and follow-up investigations) in the Kros-nowice reservoir [24]. Figure 7: Location of geological investigations (original and follow-up investigations) in the Szalejów-Görny reservoir [25]. The follow-up investigations resulted in a significant redesign of the key reservoir elements.