Simple Evaporation Method for Estimating Soil Water Retention Properties of an Unsaturated Zone in Bouhajla (Kairouan - Central Tunisia).

Soil hydraulic properties are important parameters for modeling water flow and solute transport in the vadose zone. However, direct
measurement of this characteristic in field conditions is tedious, time consuming and expensive. A simple evaporation method has been used to characterize soil water retention properties of 18 layers, constituting the unsaturated zone of a land parcel in the region of Bouhajla (Central Tunisia). This experiment requires measuring volumetric water content by the gravimetric method and pressure head by a Watermark sensor, of a small disturbed soil core, during a drying cycle under the effect of evaporation. Measured retention curves were fitted to the analytical model of van Genuchten with RETC software to estimate residual water content (θr), saturated water content (θs) and the two shape parameters α and n. Estimation results were evaluated by calculating the mean square error (RMSE) and the geometric mean error ratio (GMER). Statistical analysis has proved the success of the evaporation method for estimating van Genuchten soil retention parameters of the studied unsaturated zone.