Estimating falling rate evaporation from finite soil columns

Estimating evaporation is very important in many fields including agriculture and geo-environmental engineering. For example evaporation has a definitive role in the performance of soil covers widely used in mining and landfill applications for environmental protection. The ability to estimate evaporation from different soils without performing detailed experiments or modeling could be very useful especially during the initial stages of design. Gardner and Hillel developed an equation for calculating evaporation from finite soil columns involving the soil moisture diffusivity. The capability of the equation to predict falling rate evaporation from finite coarse sand and fine sand was studied. The studied cases were also modeled using the finite element model SoilCover. The results from the model and the equation were compared to experimental data and found to agree reasonably. The agreement indicates that the analytical solution could be used to estimate falling rate evaporation from finite columns of coarse sand and fine sand. It can facilitate the estimate of actual evaporation from soils especially in the design of engineered covers. The necessary data required are soil–water characteristic curve, the hydraulic conductivity-suction function and initial water content. The analytical method relies heavily on the soil diffusivity; hence the concepts of diffusivity and its role in water movement in unsaturated soil are also discussed.