Scaling Approach to Deduce Field Unsaturated Hydraulic Properties and Behavior from Laboratory Measurements on Small Cores

Hydraulic properties should be determined at the scale of the process modeled. The methods to hydraulically characterize a soil in situ remain extremely difficult to implement, requiring measurements of water content and pressure head with adequate time–depth resolution. We recently proposed a method that reduced the number of field measurements required for complete field hydraulic characterization. In this paper, we extend the previous method to cases where the only available information consists of laboratory hydraulic properties, along with a measurement of the maximum water content in the field, whose value depends on the way the wetting of the porous medium is performed. Specifically, the field hydraulic parameters were estimated with a scaling procedure accounting for the ratio between the total porosity estimated by the maximum water content in the laboratory and the partial porosity effectively involved in the field, as estimated by the field-measured maximum water content. The scaling method was evaluated with data from four soils (three volcanic sandy loam soils and one silty clay loam soil). Soil hydraulic properties were measured both in situ by a field internal drainage test and in the laboratory in an evaporation experiment (Wind’s method). Scaling-based hydraulic properties were also compared with those estimated by applying a simplified method based on the unit-gradient water flow assumption where only water content measurements performed during the internal drainage test were of concern. The hydraulic properties estimated with the scaling method were compared with the measured ones and with those from the unit-gradient method in terms of the Relative Mean Error (RME) and Relative Root Square Mean Error (RRMSE). The scaling method proved to be especially effective when applied to the three sandy loam soils, where scaled retention and hydraulic conductivity curves to a large extent reproduced those measured in the field. For the silty clay loam soil, appropriate results were observed only for the water retention curve, while poorer scaled hydraulic conductivity was obtained.