Variably saturated three-dimensional rainfall driven groundwater pumping model

Many water-resource management and environmental quality problems require a better understanding of the complete hydrological process which can be described only by a variably saturated groundwater flow model. A new saturated/unsaturated three-dimensional rainfall-driven groundwater-pumping model has been developed to understand the response of a variety of hydrogeologic systems to both natural and anthropogenic impacts. This model was designed to simulate all of the important elements of the hydrological cycle other than the runoff and seepage processes as accurately as possible using physically based assumptions and equations.; The uniqueness of the model is its hydrological and hydrogeological completeness such, that the model runs using rainfall and climatologic data and calculates the three-dimensional pressure distribution over the entire bydrogeologic domain. The model also calculates the potential evapotranspiration for given climatological data. In the model, the greatest effort has been devoted to an improved conceptualization of the unsaturated zone, which is a crucial part of the hydrological system in a groundwater basin. This is because the unsaturated zone plays an important role in many hydrological processes such as recharge to groundwater, surface-groundwater interaction, solute transport, and evapotranspiration.; Recent advances in modeling variably saturated flow are incorporated into the model. The model simulates the hydrogeologic system by solving the nonlinear three-dimensional mixed form of the Richards equation using the modified Picard iteration scheme and preconditioned conjugate gradient method. A new convergence criterion is used for faster convergence in the iterations. The model treats the complete subsurface regime as a unified whole, and flow in the unsaturated zone is integrated with saturated flow in the underlying unconfined and confined aquifers. The model has the capability to pumping from the aquifer and artificial recharge. A transpiration and an evaporation model are integrated into the groundwater flow equation as sink terms.; Input data for the model are the bydrogeologic and geometric properties of the flow domain, meteorological data, vegetative cover, and soil moisture characteristics. The output is in the form of groundwater heads, moisture contents, and actual evapotranspiration. The model has been verified against other model results from the literature.