Evaporation from Multilayered Heterogeneous Bare Soil Profiles

Evaporation from homogeneous and multilayered soil profiles was studied under laboratory conditions using columns packed with different sand types and containers packed with glass beads of different sizes. The impact of positive and negative permeability gradients, and the effect of layer thickness (H), has been investigated. The cumulative evaporation from the fine-to-coarse (F-C) multilayered profile is higher than the one from the coarse-to-fine (C-F) profile. The homogeneous columns evaporate more or less than the multilayered ones depending on the thickness of the layers and the characteristic length of the soil in the top layer. The trends are in agreement with the preliminary results generated by the numerical solution of the flow equations. Cumulative evaporation at the end of stage 1 increases with the layer thickness for the multilayered systems and is larger for the F-C configuration than for the C-F one. Glass beads evaporation experiments revealed the existence of a cascade of bursts of air when the invading gas phase reaches the successive fine/coarse layer interfaces in the case of the F-C configuration. While the evaporation front moves gradually downward during drying in the C-F multilayered system, it appears to move upward toward the surface in the F-C multilayered one. It is shown that soil heterogeneity has a significant impact on evaporation. Multilayered soil profiles could be harnessed to reduce water losses or to accelerate drying, depending on the sequence, the thicknesses, and the properties of the layers.