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Abstract:
The impact of rainfall events in terms of erosion, transport and flood generation strongly depends on the flow paths along which the water travels. These flow paths are influenced by initial conditions (wetness state) and driving forces (rainfall amounts and intensities) but also by the characteristics of the terrain and the subsurface. While we usually think of the first two as temporally variable, we often consider terrain and subsurface characteristics to be static. However, both surface and subsurface structures evolve over time. Knowledge of this evolution can help us to understand landscape patterns of flow processes. It is furthermore of special interest in alpine settings where the retreat of glaciers due to global warming leads to accelerated exposure of glacial moraines. We investigated how these “newborn” hillslopes respond to hydrological forcing and how structures and processes will change over time by making use of moraine chronosequences covering the first 10 millennia of landscape development. We analyzed two hillslope chronosequences in glacial forelands in the Swiss Alps, comparing siliceous and calcareous parent material. For each age class we determined soil properties and vegetation characteristics. We then investigated the hydrologic functioning of the slopes by analyzing soil moisture response times, soil water storage, dominant flow path types, and the frequency of preferential flow occurrence. Flow paths were identified by dye tracer experiments at the plot scale and irrigation experiments with deuterium-labelled water at the hillslope scale. A principal component analysis and clustering were used to identify how structure relates to hydrological responses.
