­REGIONAL HYDROGEOLOGIC CONTROLS IN AN INTERMOUNTAIN BASIN: INSIGHTS FROM GROUNDWATER MODELS OF THE SOUTH PARK BASIN, COLORADO

The hydrogeology of intermountain basins is uniquely defined by heterogeneity through large and variable topographic relief, substantial climatic differences, and complex geology. The scarcity of wells in mountain settings confounds our ability to characterize the influence of these heterogeneities on basic groundwater flow processes. As such, the development of conceptual and numerical models is both particularly challenging and useful for developing an understanding of the basic patterns and dynamics of groundwater flow in mountainous regions. To explore the role of realistic hydrogeologic heterogeneity on regional groundwater flow in a contractional intermountain basin, a 3D numerical groundwater flow model was developed for the South Park basin in central Colorado. The South Park basin was conceptualized into 4 major hydrogeologic landscapes, selected for their characteristic mountain or valley settings. These landscapes were used to regionalize hydrogeologic parameters in the development of the numerical flow model and as a foundation to explore the hydrogeologic relationship between the mountain and valley aquifers. Model results highlight fundamental differences in groundwater flow systems between hydrogeologic landscapes and emphasize the prominent role of the fold-fault belt of the master valley in controlling recharge mechanisms and groundwater flow patterns in South Park. Mountain landscape topography was found to place substantial control on the sensitivity of master valley aquifers to poorly constrained mountain hydrogeologic conditions.