Effect of Parameter Sensitivity of van Genuchten Model on Numerical Simulation of Rainfall Recharge

The van Genuchten model is frequently used in expression of soil lithology and hydraulic feature of vadose zone. The included soil hydraulic parameters are sensitive factors in numerical simulation of rainfall recharge. It facilitates the understanding of the physical meaning of parameters, improving accuracy of numerical simulation of rainfall recharge and parameters regulation to analyze the sensitivity of each soil hydraulic parameter. In this study, one-dimensional variably saturated flow models were established by using HYDRUS software. Simulations were run under conditions of multiple sets of parameters which are set in the principle of changing one parameter and keeping the others invariant to evaluate parameter sensitivity of van Genuchten model by using actual recharge quantity, recharge process curve and maximum evaporation depth as the index. The case study chose multiple sets of measured parameters to evaluate the influence of parameter variation among different samples of the same lithology. The simulations results show that maximum evaporation depth is significantly affected by the n and α which are negatively related to it; θ_s, n, and Ks have a high sensibility to the variation of vertical groundwater recharge, however they will change with porosity, grain size distribution and bulk density of soil at the same time. It is concluded that the reasonable analysis of parameter sensitivity can only be done in combination of the study of their physical meaning.