Influence of Rock Fragments in Soils on Soil Hydraulic Properties.

Rock fragments in soils have a great impact on soil water retention and hydraulic conductivity data.

As pilot project, the Hydrographic Monitoring Network of Unsaturated Zone in Austria, determines the groundwater recharge in stony soils. Objective of this study is to investigate the impact of rock fragments on soil hydraulic properties by carrying out lab experiments and by using a simulation model (HYDRUS 2D). Soil samples were taken from the site in Styria, brought to the laboratory and were air dried. The soil texture is a sandy loam with a fraction of rock fragments of 25% in the 0-30 cm soil depth and of 68% in the layer below 30 cm. Two vertical soil columns with a diameter of 46 cm and a length of 70 cm are filled: one with soil in the same composition and bulk density like the in-situ soil, the other with soil particles ≤ 2 mm. TDR probes and tensiometers are installed in 10, 25, 40 and 55 cm depth and data are obtained in 30 cm intervals throughout the experiment. Constant water application rates between 0,58 mm/h and 227 mm/h are used. Soil water retention curve, unsaturated and saturated hydraulic conductivity are determined for both soils. By comparing both data sets the impact of rock fragments on soil hydraulic properties will be derived.