Chapter 4 - Influence of Cover Beds on Slope Hydrology

Abstract

Numerous case studies carried out in the subdued mountains of Germany during the last decades have revealed that periglacial cover beds play a decisive role in hillslope hydrology. Considering the omnipresence of cover beds in sloped terrain of the mid-latitudes, knowledge of slope-water paths is crucial not only for flood forecast but also for understanding how contaminants pass through ecosystems. Since periglacial cover beds are usually composed of different sedimentary layers, they show a high spatial variability of physical soil parameters, which are, in turn, responsible for small-scale variations of the hydraulic properties. Regardless of bedrock type, the observations reported in this chapter from different regions lead to the conclusion that there is a clear relationship between subsurface layering and runoff-generation processes. The hydraulic anisotropic structure of the deepest (basal) layer is the major factor controlling subsurface water-flow paths. On one hand, this layer acts as an aquitard for seeping water because of its high bulk density. On the other hand, once water has percolated into this layer, it is able to flow in lateral directions because of the coarse clasts oriented parallel to the slope. Therefore, such a cover bed may be treated neither as an aquifer nor as an aquiclude. Besides, as a function of pre-moisture, a nonlinear runoff response to precipitation or snow-melt of the investigated catchments was identified.