REEVALUATION OF THE EVAPORATION METHOD FOR DETERMINING HYDRAULIC FUNCTIONS IN UNSATURATED SOILS

Understanding of soil water and solute transport processes requires kn owledge of the soil hydraulic properties. A simple evaporation method for the determination of the hydraulic conductivity function and the w ater retention characteristic was developed and applied to a range of sails with different texture and structure. During evaporation from th e top of a 6-cm-high soil core, sell water pressure head at 1.5 and 4. 5 cm below the soil surface was measured with tensiometers several tim es. At the same time, evaporative water toss was determined by weighin g the soil column. The procedure for calculation of hydraulic function s was evaluated via numerical simulations. Results from the numerical experiment confirm the underlying theory. A limitation of the evaporat ion method is the fact that, at water contents near saturation where h ydraulic conductivity is high, hydraulic gradients cannot be determine d with sufficient accuracy. Other measurement techniques are suggested that can supplement the evaporation method in the wet range.