Unsaturated Soil Hydraulic Properties

Abstract

In the first part of this chapter, the tension infiltrometer (TI) technique is illustrated. After having described apparatus and instruments as well as the operative procedures in the field, the solutions based on the Wooding’s equation for steady-state flow are presented. Specific focus is given to the multi-potential approaches that allow determination of unsaturated soil hydraulic conductivity, K 0, corresponding to a sequence of pressure head values, h 0, imposed on the soil surface. The analytical model proposed by Haverkamp et al. (1994) to describe three-dimensional transient infiltration from a circular source is introduced and a single-test approach is presented that allows estimation of soil sorptivity, S 0, and hydraulic conductivity, K 0, from the coefficients of two-term cumulative infiltration equation. Two linearization methods, namely cumulative and differentiated linearization, are presented to fit analytical model to experimental data. Simultaneous estimation of soil water retention and hydraulic conductivity functions by means of numerical inversion of unsaturated water flow describing an infiltration experiment conducted by the TI is then illustrated and its limits and possible improvements are discussed. Finally, hydraulic contact at the infiltration surface and particular TI devices and applications are presented. In the second part of the chapter, a simplified procedure for a complete soil hydraulic characterization, named BEST (Beerkan Estimation of Soil Transfer parameters) is presented. Firstly, the soil hydraulic characteristic curves used in BEST and the necessary data to apply the procedure are presented. Estimation of the shape and scale parameters of characteristic curves is then illustrated, taking into account the alternative estimation methods that have been developed since 2006. Points concerning the practical application of the procedure and results of investigations making use of the BEST procedure are then discussed. The chapter includes several examples that show application of both TI steady-state and transient approaches and complete soil hydraulic characterization by BEST method.