Abstract
Runoff generation mechanisms vary between catchments and despite decades of research in many catchments, these mechanisms are still not fully understood. In this paper, runoff generation mechanisms in the steep pre-alpine catchments in the Alptal, Switzerland, are discussed. These fast responding catchments are characterized by low permeability soils on top of flysch bedrock. In combination with the high and frequent precipitation, this results in predominantly wet conditions. In many areas, the water table is close to the surface. We review the main results of recent (2009-2016) studies in these catchments that used isotope, stream chemistry and hydrometric data. These field studies focused on the spatial and temporal patterns in groundwater levels, spatial patterns in the isotopic composition and chemistry of streamflow during baseflow conditions, as well as the responses of streamflow and its isotopic composition during rainfall events. The combined results of these studies highlight the establishment of connectivity of areas with a different topographic position and areas with a different land use during rainfall events. They also show the importance of flow in higher conductivity near surface soil layers for runoff generation, as well as the frequent occurrence of surface runoff. Spatial differences in groundwater dynamics are related to topography. Streamflow responses are mainly affected by the rainfall characteristics; differences in streamflow and hydrochemistry between catchments with different portions of forest, meadows and wetlands, were relatively small. However, variations in the chemistry of baseflow along stream reaches within a catchment were considerable. Above all, these studies highlight the value of combining data on spatial patterns of groundwater levels and stream chemistry with long term data on streamflow to derive a more complete picture of the dominant runoff generation mechanisms.
van Meerveld, H J