NEW METHOD FOR DETERMINING HYDRAULIC PROPERTIES OF UNSATURATED SOIL USING EVAPORATION DATA

Abstract

Solving soil unsaturated flow problems requires knowledge of the water retention θ(ψ) and unsaturated hydraulic conductivity k (θ) relationships.This study introduces a new evaporation method for simultaneous estimation of both retention and unsaturated hydraulic conductivity data. Newton-Raphson iterative method was used to solve non-linear equations in time. Simultaneous transport of liquid and vapor flow in the unsaturated soil was modeled. Evaporation from a vertical column of soil material (tile) was simulated. Hydraulic parameters were estimated by minimizing the sum of squared differences between measured and simulated evaporation rate through the whole period of the experiment. Two laboratory experiments were carried out on the same sample under different conditions to evaluate the ability of this new method to provide good estimation of the retention and unsaturated conductivity curves. The results show that this method is stable, accurate, and can be applied for other types of soil.