Estimation of Philip Equation Sorptivity Factor by Two Methods Using Disc Permeameter

Determination of unsaturated soil hydraulic parameters are important for assessment and understanding of many processes. These processes include as: runoff and rainfall infiltration, salt, contaminations and nutrition elements transmission in soil and solution absorption by plant root. Recently, disc permeameter has been recognized as one of most current tool for measurement of unsaturated soil surface hydraulic parameters. In this research, for study of relation between unsaturated soil hydraulic conductivity and sorptivity curve,the field experiments were performed at six iterations to interval of 1 meter each other on three zons (first zone with silty loam texture, second and third zone with loam texture). At all iterations, steady infiltration rates were measuremented on soil surface in consective five suctions, 15, 10, 6, 3 and 0 cm recpectively. Then, sorptivity factors in each suction were estimated by methods of differentiation (unsteady analysis) and steady analysis. The results of this study indicated that, sorptivity curve (s(h)) similar as unsaturated hydraulic conductivity curve (k(h)) is followed an exponential function. Sorptivity factor had inverse relation with suction, so that sorptivity value increased with suction reduction. Also, the results of this study showed that unsteady analysis method estimate sorptivity value at all suctions more than steady analysis method and the differences are significant in suctions of 3 and 0 cm. The study results indicated soil sorptivity factor inverse relationship with α parameter and α parameter inverse relationship with soil structure resistance degree. Also, it is observed that sorptivity factor sensitivity to soil structure is more than hydraulic conductivity.