Determining the influence of stones on hydraulic conductivity of saturated soils using numerical method

Mountainous soils usually contain a large number of rock fragments (particle diameter > 2 mm), which influence soil hydraulic and retention properties. Data characterizing the properties of these soils usually describe only the fine earth (particle diameter < 2 mm). To quantitatively describe soil water movement in stony soils, their most important characteristic, i.e., the effective saturated hydraulic conductivity (Kse), must be known. The objective of this study was to use a numerical method for estimating the saturated soil hydraulic conductivity that depends on relative stone content (stoniness), and sizes and shapes of stony parts. The method is based on a numerical version of the classical experiment of Darcy. The steady-state water flow under a unit hydraulic gradient through hypothetical soils containing stones was simulated using the two-dimensional simulation model HYDRUS-2D. Four soil textural types were considered. Special attention was paid to the moraine soil from the FIRE site in High Tatras. A relationship between the relative saturated hydraulic conductivity, Kr, and the relative stone content, Rv, was derived. Kr(Rv) function is decreasing slower for larger stones. Numerical results were used to propose an empirical equation to estimate Kr of soils containing rock fragments of a spherical shape of various diameters.

Research Highlights
► Hydraulic conductivities of saturated stony soils K, were estimated using numerical method.
► K of saturated stony soils decrease nonlinearly with the relative stone content.
► K of saturated stony soils decrease faster for stones with a smaller diameter at the same stoniness.