Prediction of hydraulic conductivity and sorptivity in soils at steady-state infiltration

The purpose of this study was (1) to find a matching factor (u) between infiltration rate and hydraulic conductivity during steady-state infiltration, and (2) to propose equations based on infiltration and soil moisture-retention functions for prediction of the hydraulic conductivity K(theta) within the rapidly (non-capillary) drainable pores (RDP) and capillary-matrix pores of soils. The K(theta) of capillary pores was divided into K(theta)(SDP), K(theta)(WHP) and K(theta)(FCP) within slowly drainable pores (SDP), water-holding pores (WHP) and fine capillary pores (FCP), respectively. Five soil profiles of calcareous sandy loam, alluvial saline and non-saline clay, located at the Nile Delta, were used to apply the proposed equations. The highest and the lowest values of K(theta)(RDP) were observed in calcareous and saline clay soil profiles, respectively. Values of K(theta)(RDP) remained higher than those for capillary pores in the studied soils. The predicted values of K(theta) in capillary and non-capillary pores classes were in the expected range for unsaturated hydraulic conductivity. Water sorptivity (S) was determined at initial unsaturated soil water conditions and calculated at steady-state infiltration (S-w) using a derived equation. There was a decrease in S with an increase in soil water content; i.e. at steady-state infiltration, S decreased by 35-40% in calcareous soils and by 45-60% in alluvial clay soils. The parameter values of u and S-w tended to be uniform in calcareous soils, but nonuniform in saline and non-saline clay soils.