A Hysteretic Model of Hydraulic Properties for Dual-Porosity Soils

We propose a hysteretic model of hydraulic properties for dual-porosity soils based on the bimodal van Genuchten model and Kool and Parker (K&P) hysteresis model. Hysteresis is considered only in the first pore domain, affecting mainly higher water contents, while a nonhysteretic behavior is assumed in the second pore domain, affecting mainly lower water contents. The main drying and wetting curves are described with the same set of parameters except for alpha(1), which is different for the drying and wetting curves. The scanning hysteresis loops in the first subregion are also described using the K&P model. The hysteretic water retention model agrees reasonably well with drying and wetting retention curves and scanning loops observed for Andisols. Although the corresponding unsaturated hydraulic conductivity, evaluated using the Mualem pore-size distribution model, as a function of the water content, K(theta), is nonhysteretic for higher water contents, unrealistic hysteresis occurs in K(theta) for lower water contents. To obtain an "almost" nonhysteretic K(theta) function for the entire range of water contents, an additional constraint on the value of the alpha(1) parameter for K(theta) is imposed, and a single value is used for both drying and wetting curves.