Reevaluation of the Evaporation Method for Determining Hydraulic Functions in Unsaturated Soils

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Abstract
Understanding of soil water and solute transport processes requires knowledge of the soil hydraulic properties. A simple evaporation method for the determination of the hydraulic conductivity function and the water retention characteristic was developed and applied to a range of soils with different texture and structure. During evaporation from the top of a 6‐cm‐high soil core, soil water pressure head at 1.5 and 4.5 cm below the soil surface was measured with tensiometers several times. At the same time, evaporative water loss was determined by weighing the soil column. The procedure for calculation of hydraulic functions was evaluated via numerical simulations. Results from the numerical experiment confirm the underlying theory. A limitation of the evaporation method is the fact that, at water contents near saturation where hydraulic conductivity is high, hydraulic gradients cannot be determined with sufficient accuracy. Other measurement techniques are suggested that can supplement the evaporation method in the wet range.

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