The Concept of Matric Flux Potential Applied to Simulation of Water and Salt Movement in Unsaturated Soils

Water and salt simulation models based on Darcy type (conventional) and matric flux potential based (proposed) numerical schemes were compared. Both graphical and statistical means were used to evaluate the model performance. Comparison of simulated results with the primary field data showed that the proposed matric flux potential based simulation model could not only lead to an exact representation of temporal-profile ofmoisture distribution, during both wetting-drying cycles, but could also give more exact estimate of profile soil moisture contents (R² = 0.75). The conventional computational algorithm, on the other hand, could neither give near-realistic representation of progressive drying of top soil layers nor accurate profile soil moisture content estimates (R² = 0.26). Consequently the evaporation and the top soil layer salinization processes simulated through matric flux potential model were more near-realistic than those simulated through conventional model. In the conventional approach, one of the greatest difficulties is deciding upon a method for averaging hydraulic conductivities of adjacent compartments. The use of matric flux potential method eliminated this problem. Another asset of the matrie flux potential is that it gives a characteristic smooth curve when plotted as a function of water content. Because these curves are asymptotic to some maximum value, the flux of water in very low range of water contents was found to be small, regardless of the magnitude of the gradient in water content. Thus, very little error in predicted fluxes results even when one simply extrapolates these curves. Hence accurate measurement ofmatric potential and hydraulic conductivity in low water content ranges was not necessary with the proposed model.