The dam of the storage power station Freibach in Carinthia (Austria) is founded in a sequence of quaternary, glacial loose sediments, which form a system of superimposed aquifers. In these sediments, a considerable loss of drainage water occurs, causing springs on the downstream side of the dam.Drainage waters can cause erosion of a dam or bedrock. Especially on the downstream side loose material can be washed out. This may lead to a decrease of stability or, in an extreme case, to failure of the dam. Many potential reservoir sites in the Alps are shaped by glacial erosion and sedimentation processes. Therefore, the interaction of artificially created reservoirs and the existing groundwater horizons in these glacial sediments is an important factor for the functionality and stability of a dam.Goal of this master thesis was the hydraulical characterisation of this aquifer-system, based on long-term monitoring data of spring discharge and groundwater table. The catchment area was mapped geologically and hydrogeologically and additional measurements in selected piezometers were taken. With analytical solutions of the available data, the hydraulical influence of the reservoir on the complex aquifer-system and its drainage-dynamic was examined. Questions like the reaction of the groundwater after storage level changes, which aquifers are responsible for spring recharge and if the aquifers are hydraulically connected or isolated, were discussed. Furthermore, a numerical model of one of the main aquifers was generated, which shows the basic dynamic of the groundwater system.