Rainfall induced soil seal (B) Application of a new model to saturated soils

A conceptual model is proposed in which the saturated soil seal (crust) properties are derived on the basis of physical concepts estimated empirically. The reduced hydraulic conductivity of the soil surface is attributed to its decreased porosity and increased "ineffective" water content. The characteristics of the modeled soil seal were examined using data of sandy loam and loam (loess) soils. An inverse approach was applied for calibration using infiltration rate data. The results indicate that the importance of the 0.1 mm compact clay and silt seal layer, the "skin", has been overestimated. The sealing of bare soils formed under highenergy rainfall cannot be attributed to the skin. The suggested theory allows the seal properties, including its thickness and hydraulic conductivity, to vary with respect to rain and soil properties as well as the flow boundary conditions. Seal thickness, hydraulic conductivity and conductance were calculated as a function of the driving hydraulic head for the two soils. The sandy loam had a thicker sealing layer with higher hydraulic conductivity (and sensitivity to flow conditions) than the loam. While the hydraulic conductance of the loam seal decreased slowly as a function of the hydraulic gradient, the conductance of the sandy loam soil dropped sharply with an increase in the hydraulic gradient, and reached a lower value than that of the loam for large gradients.