ABSTRACT
Transportation of water and contaminants through unsaturated soils is one of the most important natural phenomena. This has been predicted and determined by soil hydraulic characteristics or parameters based on empirical data or theoretical approach. However, it is still a challenge to achieve accurate hydraulic conductivity due to its large spatial variability. It’s necessary to review the presented models and techniques thus to provide the guide for accessing hydraulic conductivity of unsaturated soils accurately. In this review, the methods or models to estimate and measure the hydraulic conductivity of an unsaturated soil are discussed, evaluated, and compared in detail. These include numerical simulation method and inversion model, fractal model, soil morphological model, and direct field test methods. The van Genuchten model is applicable for almost types of soils and the disc infiltrometer method is well suitable to direct measurement of the hydraulic conductivity of a soil on a large scale. In conclusion, standardization of soil hydraulic parameters in models and calculations as well as applying new techniques/equipment are necessary for better accuracy of determining the unsaturated hydraulic conductivity of a soil.
