DETERMINATION OF UNSATURATED HYDRAULIC CONDUCTIVITY BY INTERNAL DRAINAGE ASSUMING A UNIFORM SOIL WATER PROFILE

The internal drainage procedure may be used to measure the soil unsaturated hydraulic conductivity (UHC) by measuring the soil water content and matric potential profiles. However, in some cases this method can not be used due to failure of tensiometer in determination of soil matric potential. Therefore, a simplified procedure may be applied. In the present investigation a modified internal drainage method was used and compared with the original procedure to determine the UHC in three different soils. In this simplified method, it was assumed that a uniform soil water profile or unit hydraulic gradient was assumed. The simplified procedure only requires the soil Water profile to be measured by a neutron probe or by the gravitational method. The equation of UHC as a function of soil water content, K(theta), obtained by the two different methods was similar for two of the three soils (Dezful and Mollasani) which contained no gravel. In these soils, the soil water profiles were rather uniform and their hydraulic gradients were about 1.0 and 0.92 which are close to unity. Therefore, it may be concluded that the simplified method of internal drainage can be applied to homogeneous soils with a nearly uniform soil water profile and unit hydraulic gradient. The K(theta) for gravelly soil (Jahrom) was different in the two methods due to the nonhomogeniety of soil and non-uniform soil water profile.