Estimating Saturated and Unsaturated Hydraulic Conductivities of Sloping Lands under Steady and Transient States

Double ring and tension infiltrometer are simple, fast and suitable instruments for determining soil hydraulic conductivity. The effect of land slope on soil properties such as saturated and unsaturated hydraulic conductivities has been reported by various researchers. The aim of this study was to estimate and compare soil hydraulic conductivities at different slope gradients under steady state and transient flow regiones. Field experiments were conducted in a loamy soil with different slope gradients in Gonbad research station, Hamadan, Iran. Soil surface slope gradients, of 0 (level), 10, 20, 30 and 40 degree were selected in this station. For each slope gradient, water infiltration experiments were carried out using a double ring and a tension infiltrometer at tensions of 0, 6, 9 and 15 cm in three replications. Totally 60 infiltration experiments were carried out. In steady state, values of saturated and unsaturated hydraulic conductivities were estimated using Reynolds et al. and Ankeny et al. procedures, respectively. In transient statevalues of the hydraulic conductivity, for different land slopes and water pressure heads, were calculated from the parameter of the second term of Philip’s two-term equation, Results indicated that the hydraulic conductivity values for both steady state and transient flow regines were decreased with increasing in tension and slope gradient values. The higher rate of hydraulic conductivity decreases was obtained for lower tensions. In steady and transient state, by increasing in slope gradient from 0 to 40 degrees, decreasing of hydraulic conductivity in 0 tension was 4.1 and 3.7 times more than these in 15 cm tension, respectively. The fitness between the Gardner exponential model and steady state flow procedure was higher than that of transient flow procedure. In all experiments, values of relative difference of hydraulic conductivities were less than 7% that indicated good fitness between the steady state and transient flow procedures