The unsaturated zone is characterized by complex water and mass transport processes, which are strongly influenced by meteorological parameters and thus also directly by climate change. The interrelationships between atmosphere, biosphere and subsurface, as well as the intermediate storage of water and redistribution by evapotranspiration, surface and intermediate runoff, play a decisive role.
The aim of the project is to clarify the extent to which heavy rainfall events or extreme climatic conditions and snowmelt affect runoff and the soil water balance, and thus ultimately groundwater recharge.
A large lysimeter at the Karlsruhe West landfill site serves as a test field, providing complete data series over the last 10 years. Preferential flow paths for water transport seem to be of major importance there. During a precipitation event, the soil water is transferred by means of pressure transfer through rainwater inflow (piston flow); however, the penetrating water often seeks an alternative path through root passages, cavities created by organisms and existing cracks. On the basis of marking experiments, the essential transport parameters and the question of the degree of distribution of these pathways will be clarified.
A runoff component parallel to the slope is also suspected. This phenomenon could be demonstrated by comparing the runoffs of two adjacent subfields arranged in a fall line (see Figure 1, B below and B above). However, it is not yet clear which parameters in detail have an influence on the ratio of the two runoffs.
Profile of the lysimeter test field. Built up from 5 layers: Recultivation layer, drainage layer, mineral sealing layer, capillary layer, capillary block.
Temporal variation of soil moisture at measuring point NS7. Precipitation and surface runoff are shown for comparison.