COUPLED SOIL-ATMOSPHERE MODELING FOR SOIL EVAPORATION

Traditional methods of evaluating evaporation provide an estimate of t he maximum or potential rate of evaporation determined on the basis of climatic conditions. Methods such as these are appropriate for open w ater or fully saturated soil surfaces. Actual rates of evaporation fro m unsaturated soil surfaces are generally greatly reduced relative to the potential rate of evaporation. A theoretical model for predicting the rate of,evaporation from soil surfaces is presented in this paper. The model is based on a system of equations for coupled heat and mass transfer in soil. Darcy's Law and Fick's Law are used to describe the flow of liquid water and water vapour, respectively. Heat flow is eva luated on the basis of conductive and latent heat fluxes. Dalton's Law is used to calculate the rate of soil evaporation to the atmosphere b ased on the suction at the soil surface. The soil-atmosphere model was used to predict soil evaporation rates, water-content profiles, and t emperature profiles for a controlled column evaporation test over a 42 day period. The values computed by the soil-atmosphere model agreed w ell with the values measured for two columns of Beaver Creek sand in t he evaporation test.