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Verification of flow processes in soils with combined sprinkling and dye tracer experiments


Presented at the IAHS International Workshop, Runoff Generation and Implications for River Basin Modelling
Freiburg, Germany, 2000.






Water flow in soils is strongly governed by macropores, the heterogeneity of the soil matrix and the exchange of water between the macropores and the soil matrix (interaction). The magnitude of interaction strongly influences the runoff generation process in soils with macropores during extreme rainfall events. A low interaction in combination with low permeability in the subsoil produces rapid overland flow. Low interaction in combination with permeable lateral flow paths in the subsoil results in bypassing of the topsoil and the generation of subsurface flow.
The water movement during infiltration and the resulting flow paths were studied with sprinkling experiments using a dye tracer under different rainfall intensities and soil moisture conditions. The dye tracer was continuously applied with the rainfall on 1 m2 plots. After the sprinkling, cross-sections of the soil were prepared for surveying horizontal and vertical dye patterns, thus displaying the cumulated flow path in the soils. These experiments were made on sites with different infiltration behaviour. The results are used to illustrate and study the influence of the water exchange between macropores and the soil matrix on runoff generation. The experiments also demonstrate the dependence of flow processes on properties like water repellence near the soil surface and soil structure. Thus, the verification of flow processes in the field can be improved with combined sprinkling and dye tracer experiments.