Evaluation and application of the modified van Genuchten function for unsaturated porous media

Proper expressions of unsaturated soil hydraulic properties, e.g., water retention curve (WRC) and relative hydraulic conductivity (RHC), are essential for studying groundwater hydrological processes. Various mathematical expressions have been proposed to describe these properties. Based on the published data composed of 27 types of soils covering a wide range of soil textures from sand to silt clay loam, we proposed and evaluated a new set of VG model (named as MVG model), composed of the WRC proposed by Troch (1993) (the MVG-WRC model) and RHC suggested by Kong et al. (2016) (the MVG-RHC model). Comparison shows that the MVG model is more accurate and flexible than existing soil hydraulic functions, especially for predicting the RHC. In addition, relationships between fitting parameters of the MVG-WRC and MVG-RHC model have been established for possible parameter derivation based on each other in actual application. Furthermore, the expressions of the MVG model are easy to integrate and differential to derive the analytical solutions, including the wetting front pressure Ψ_f, which is essential in Green and Ampt model for ponding infiltration analysis, and the characteristic length L_c, which is the key factor for determining the flow processes (e.g., drainage or evaporation) in unsaturated porous media.