One of the most important hydrualic properties of soils is the unsaturated hydraulic conductivity which it’s field measurement is both expensive and time consuming process. Furthermeore due to variability of this property both in space and time, the limited data obtained from these measurements can not be use for practical field situations. Due to this limitation a number of methods for estimating unsaturated hydraulic conductivity have been devised which use some easily determined soil properites for this purpose.
one of these methods is due t, Mualem (5) whose eqation is a modified Burdine types equation. There are some disagreement about the value of power P in both Burdine and Mualem equations. Recently Van Genuchten(10) solved both equations with variable P. In the present paper we have used Van Genuchtens Solution with variable P for a wide variety of different soils.
The results of this paper has shown that P.: does not have a fixed value of0.5 as suggested by Mualem for. all textural soil groups. We also found that the disappointing results of Alexander(1) and others was m•inly due to assumption of a fixed value of: 0.5 for P. According t the results of this work the value of P for clayey, loamy, and sandy soils was equal t 2.5, 0.5 and 1.5—6.5 respectively. The solution was not sensitive to residual water content (?r) as suggested by Mualem, but the sensivity was mainly due to saturated water content ( ?s).
)