| Recharge rates are one of the most poorly constrained hydrogeologic parameters in the majority of groundwater-flow models, though methods for determining the spatial distribution of recharge have been intensively researched. The method presented in this thesis utilized a previously constructed three-dimensional geologic framework model as the hydrostratigraphic framework for a three-dimensional numerical, variably-saturated, groundwater-flow model. The Huntertown Aquifer System in Allen County, Indiana serves as the study area, exhibiting a unique hydrogeologic setting containing glaciofluvial and glaciolacustrine facies interbedded with discontinuous tills. Outputs from a 30-day groundwater-flow simulation included 3-D flow vectors at every calculation cell within the model. By extracting the vertical component of flow at the water table, potential recharge-discharge relationships throughout the model domain were identified. Interpretation of these relationships yielded derivative maps of spatially distributed precipitation-driven recharge, discharge, unsaturated thickness, and aquifer sensitivity to near-surface contamination. In a comparison of methods for aquifer-sensitivity mapping in Allen County, the groundwater-flow model produced similar patterns to those produced from more conventional methods. However, the model-produced aquifer-sensitivity map provided a greater level of detail since it incorporated several critical factors that influence recharge such as the heterogeneous sedimentary structure, degree of confinement, and secondary permeability of the aquifer. This thesis shows that through the combined application of 3-D geologic mapping and hydrologic modeling, we can produce a variety of derivative maps as value-added products that can be applied to water-resource issues. |
