Modeling the effects of climatic changes on groundwater flow and solute transport systems

There were two primary objectives of the present study. The first was to modify existing groundwater flow and solute transport models so that they could be coupled to both a surface-hydrology model and to atmospheric circulation models. In this way quantitative estimates of groundwater recharge can be made based on projections of temperature and precipitation. The second objective was to develop a computer program that takes into account the effects on aquifer parameters of recharge-driven changes in pore-pressure. This pore-pressure model, which is coupled to the climate and water models, computes the spatial changes in pore pressure and then estimates new values of hydraulic conductivity, porosity, and specific storage. Currently, the pore-pressure model is based upon an empirically-derived relationship between changes in effective stress and permeability for fractured-carbonate rocks. A model that estimates changes in dispersivity based on the scale of a solute plume was also incorporated into the suite of models. Two suites of groundwater models were created; one consisting of three-dimensional models using finite-difference methods and the other consisting of two-dimensional models using finite-element methods. Idealized data sets were constructed to demonstrate the operation of the groundwater model suite and the surface-hydrology model. Results from these simulations showed that groundwater flow rates and flow paths can be significantly affected by recharge-driven changes in pore pressure and by subsequent changes in hydraulic conductivity. The simulation results also showed that changes in hydraulic conductivity are not strictly a function of changes in head, but are also a function of the relative position of the land surface and water levels. Maximum changes in conductivity were found to take place in areas where the initial pore pressure to total stress ratio was high. A sensitivity analysis showed that the hydraulic heads in a system are more sensitive to initial conditions of effective stress for aquifers that are relatively thin and also for aquifers with relatively small values of hydraulic conductivity. Hydraulic head was found to be slightly more sensitive to initial conditions of lower effective stress than higher effective stress