A study of variably saturated numerical model for groundwater flow

The purpose of this study is to develop a Finite-Analytic numerical model to calculate moisture and heat fluxes across the soil-atmosphere interface and the vertical distribution of soil moisture and temperature for the bare soil in the unsaturated zone. With more accurate flux estimates, micrometeorology related and natural ground water recharge predictions are likely to be improved.
The study contains the following features: (a) It utilizes the equations for moisture and heat transfer following the works of Chen (1995), and reforms the heat flux at the surface boundary condition for evaporation. (b) It accounts for the temperature effect in the metric head and hydraulic conductivity and uses the experimental results of Hopmans and Dane (1985) to calculate the metric head and the water capacity as functions of temperature. (c) It uses the method of de Vries (1975) to calculate the thermal conductivity as well as the correction factor for the average macroscopic temperature gradient. Both are decided by water content and the volumetric fraction of quartz and clay. (d) It applies a Finite-Analytic Numerical Model for efficient solution of strongly non-linear problems for abrupt changes in atmosphere and soil conditions. (e) The results are tested against field measurements, Jackson (1973) and Jackson et al. (1973). Including surface energy-balance components, water content and soil temperature.
According to the results, the simulated and observational trends of the soil water content are difference at begging. With few hours ago, the effect of initial condition is reductive and than the simulated and observational trends of the soil water content is closer to closer. The simulated values of the soil temperature also can response the reasonable physical phenomenon. In the process to calculate the metric head and soil temperature, the convergence and the calculating time of metric head is harder and longer than soil temperature. Otherwise, hydraulic conductivity, soil surface roughness length, and sky cover will influence the varies of soil moisture and soil temperature. The hydraulic conductivity controls and regulates the water movement upward to the surface or downward to the groundwater table where the evaporation or infiltration occurs. The surface roughness length controls the value of mass transfer and sensible heat transfer coefficients, which affects the evaporation rate, latent heat fluxes, and sensible heat flux. The sky cover determines the quantity of solar energy, which can produce significant differences in water content, soil temperature and evaporation rate.