The studied area is located in the Upper Vipava valley, in South-Western Slovenia. The research covered a wider area of the Mlake military shooting range, which is located near the H4 Razdrto–Vipava road at the foothills of mountain Nanos. Tectonic deformations in the underlying rocks occur due to the specific geological situation of the area, where Mesozoic carbonates are thrusted onto Paleogene siliciclastic rocks. The erosion of the carbonate rocks, in combination with steep slopes, causes extensive gravel deposits near the bottom of the Upper Vipava valley. The groundwater therefore prefers to flow at the boundary between the upper layers which consist of highly permeable gravel, and the lower flysch layers, which have low permeability values.
In 2008, the Slovenian Army acquired a new shooting range in Mlake, which is dug into the slope at its North-Eastern corner. After each major rainfall event, despite the installation of drainage shafts and pipes, problems with rising groundwater level and, as a result, leaks occurred shortly after its construction.
The geological and geomorphological characteristics of the area were determined through field mapping which included the study of the position and orientation of flysch and slope deposits at the edge of the Mlake shooting range. Lidar and digital elevation model processing techniques in QGIS 3.4 were utilized in the construction of the final geological-engineering and geomorphological map in the scale of 1 : 7500. To further complement the constructed map, I also calculated the current volume of the deposited fossil landslide that consists of gravel and is located at the edge of the Mlake shooting range.
The results of the field work show a large number of springs located in the fossil landslide area. These springs could possibly represent an inflow of water into the lower parts of the landslide, exactly where the shooting range is dug into the foot of a slope. The water causing the flooding of the shooting range, originates from the boundary between the lower tectonically fractured less permeable flysch and the upper fossil landslide consisting of more permeable gravel.