Rainfall intensities of 10 and 60 mm/h were applied to two grassland plots.
The experiments were first performed on dry soils, and then repeated on wet soils.
A dye tracer (Brilliant Blue FCF) was continuously added to the sprinkling water.
After the sprinkling, several vertical and horizontal cross-sections were excavated.
On these sections, the added dye tracer clearly showed the highly heterogeneous flow pattern
of the infiltrating water. The dye-covered soil sections were photographed and image analysis
was applied to classify the stained areas, which consists of a new robust supervised
classification technique. The dye tracer distributions indicate highly preferential flow
mainly due to cylindrical macropores and soil heterogeneity. The preferential flow was
dominant even under low rainfall intensities and low initial soil moisture content.
The contrasting infiltration process of the two sites can be explained by the higher and
lower water exchange between the macropores and the surrounding soil matrix.
Different methods were applied to quantitatively describe the preferential flow pattern
and to compare the flow regime of the different initial soil moisture conditions and