IMPROVED UNDERSTANDING OF A KARST AQUIFER SYSTEM THROUGH UTILIZATION OF A 3D GEOLOGIC MODEL, BUFFALO NATIONAL RIVER, ARKANSAS

Recharge and ground-water flow within a karst environment can be difficult to comprehend without intimate knowledge of the stratigraphic and structural features that may affect ground-water flow. Dye tracer studies have long been utilized to help decipher the complex nature of these systems, but the probable subsurface path the dye tracer takes from input site to detection site can be difficult to convey. However, dye tracers used in connection with a 3D geologic model allows the spatial framework of ground-water flow to be communicated quickly and effectively. Recent mapping of the Davis Creek area, a tributary to the Buffalo National River, coupled with dye tracer study results have identified a complex recharge system for Mitch Hill Spring, one of the largest springs in the park. Studies indicate contributions to this spring include interbasin flow from the Crooked Creek drainage to the north, which in turn adds to a stretch of surface flow and recharge of the Ordovician Everton Formation at a local structural high north of the Mill Creek graben. The transition across the Mill Creek graben may define an area of ground-water exchange between karst aquifers hosted by the Everton Formation and the Mississippian Boone Formation. Discharge at Mitch Hill Spring is coincident with a structural high bringing the lowermost Everton Formation to the surface near the bottom of the Buffalo River valley. These structural features are accurately depicted in the 3D geologic model, which is controlled by the geologists' interpretation in the form of geologic contacts and structure contours created from detailed geologic mapping. The 3D geologic model removes the difficult, yet otherwise necessary, task of projecting geologic units and structures into the subsurface. Visual inspection of the model allows the investigators to better conceptualize possible ground-water flow paths and is effective when used to convey results for purposes of resource management.