Flow paths in a full scale model

For the restoration of groundwater and for an assessment of its pollution by agrochemical, e.g. pesticides, and industrial contaminants, an intensive study of flow processes through the unsaturated near surface vadose zone is necessary. Such a study is being presently carried out by a joint effort of the Institute of Geophysics and the Institute of Water Management and Landscape Ecology of Kiel University. It was known from many field experiments with tracers that rain water does not penetrate the upper vadose zone as a uniform water "front", but prefers "preferentiaI" flow paths (ScanIon et al., 1997: Hagrey & MichaeIsen 1996). This is due to organic heterogeneities caused by wormholes and roots and by inhomogeneities like a variability of soil textures, background humidity or water repellence (Ritsema et al., 1993; Hagrey & MichaeIsen, 1998). A preferential flow leads to an increase of flow velocity and diminishes the filter effect of the subsurface (Kung, 1993). A full-scale model of homogeneous sand regarding the vadose zone, was needed to develop a suitable high resolution mapping technique in space and time, using different geophysical and hydrological sensors to be distributed in the sand.