Modeling Transient Evaporation from Descending Shallow Groundwater Table Based on Brooks–Corey Retention Function

In arid and semi-arid regions a large amount of rainfall and irrigation water that enters into the soil is lost through soil surface via evaporation. In such regions, there are some areas with shallow groundwater table, evaporating huge amounts of water and accumulating salts at the soil surface. Thus, the evaporation phenomenon not only is responsible for water loss but also is a major reason for soil salinization. The objective of this study was to develop and verify an analytical model for one dimensional transient unsaturated upward flow from water table to soil surface. Consequently, an analytical solution was developed based on the Richards equation with initial and boundary conditions governing evaporation phenomenon. The parametric Brooks and Corey retention function was used to describe water status in the vadose zone. Based on the proposed model, the saccumulative evaporation is estimated as function of water table drawdown and soil retention parameters. To collect the data required for model verification, nine large lysimeters were constructed and packed with sandy loam, silty clay loam, and silty clay soil textures. The results indicated reasonable agreements between the experimental data and those predicted with the proposed model. Although the overall predicted results were well resemble the real conditions, there were some underestimations for a certain period. This can be attributed to evaporation from side gap of columns, upward flow due to vapor phase movement of moisture, and the collapse of macropores resulting from soil packing. Copyright Springer Science+Business Media B.V. 2009