An improved Mualem–Van Genuchten method and its verification using data on Beit Netofa clay

Abstract

An improved Mualem–Van Genuchten method for estimating soil hydraulic conductivity in the vadose zone from data on filtration coefficient and water-retention capacity of soil is proposed. The approach offered by Kosugi for a functional description of hydraulic conductivity of soil is applied. To calculate the values of hydraulic conductivity by Mualem’s formula, the function of differential water capacity of soil with interpreted parameters has been used instead of the function of integral water capacity of soil, which describes the water-retention capacity of soil. Approximations to functions of soil water-retention capacity and hydraulic conductivity are offered here. On the basis of some concepts on the specificity of the curve that describes soil water-retention capacity, a technique for identification of these parameters is developed. The experimental data from two parts of capillary pressure range, on which the water-retention capacity of soil is measured, are used in the technique. The first part corresponds to the zone of mainly film moisture, where the sorption component of the capillary-sorption forces retaining the water in the soil predominates. The second part includes (a) the zone of the mainly capillary-suspended moisture, where the capillary component of the capillary-sorption forces predominates, and (b) the zone of the capillary-backed moisture. The improved method for estimating relative values of hydraulic conductivity of soil has been verified with the use of measured data for the Beit Netofa Сlay soil. The advantages of this method include (a) the ability to identify parameters of the soil hydrophysical functions using relatively available soil indices and (b) the higher accuracy of calculating the soil hydraulic conductivity in comparison with the original version of the method.