Periglacial Slope Deposits and Saprolites Controlling Water Discharge. Examples From the Bavarian Forest, Germany and Boulder Creek (CZO), Colorado, USA

Periglacial slope deposits are widespread in Pleistocene non-glaciated areas. They are part of the critical zone, the uppermost layer between surface and the lowest groundwater level and responsible for layer- characteristic soil water movements. These are hydrological processes like interflow and storage, depending on the sediments which are divided into Upper- (Hauptlage), Middle- (Mittellage) and Lower Head (Basislage). Their properties are governed by their genesis at different climates and according to periglacial morphodynamics. Additionally, bedrock geology and sedimentology are influencing factors. In the low mountain ranges of crystalline basement rocks, the bedrock is mostly weathered to saprolite. The significance for lateral and vertical water discharge within the critical zone is not well known and builds a major goal of this study. Especially the transition zone between periglacial slope deposits and saprolite is in the focus of interest. In the study area of the Otterbachtal, Bavarian Forest, Germany, volumetric water content is measured by FD-probes within the different layers. Sedimentological data is collected using refraction seismic prospection and interpolated to the scale of the slope catchment. Physical and chemical soil parameters are determined on samples from profile pits along a representative catena. Therefore, a complete series of water content measurements is available for the last three hydrological years. The results show seasonal typical curves with major fluctuations in water contents occurring in the Upper Head. This is ascribed to good permeabilities and rapid infiltrations within this layer. Permanent high discharge values can be found in the Lower Heads. There is no dependence on the amounts of precipitation visible, thus, they are interpreted as interflow. The saprolite is characterized by approximate constant data, possibly proven by water storage. The transferability of the results to other regions is aspired by comparable investigations in the Colorado Front Range at Boulder.