INVESTIGATING FLOW PATHS IN A SHALLOW, MANTLED-KARST AQUIFER USING APPLICATIONS OF CONTINUOUS MONITORING AND HYDROGRAPH RECESSION LIMB ANALYSIS AT THE SAVOY EXPERIMENTAL WATERSHED, NORTHWEST ARKANSAS

The Savoy Experimental Watershed (SEW) is a University of Arkansas property that encompasses about 1250 hectares in the mantled-karst of the Springfield Plateau in the southwestern Ozark Plateaus. SEW is a long-term, integrated, and multidisciplinary field laboratory where processes, controls, and hydrologic and nutrient–flux budgets for surface water, soil, and shallow ground-water environments may be evaluated in a well-characterized and well-instrumented setting.

Previous studies at SEW established a three-component model consisting of the interface (soil) zone, interflow (epikarst) zone, and a focused flow (phreatic) zone. Permeability contrasts between these zones and within the aquifer are the primary control of ground-water flow, with structural features forming a secondary control. In this setting, water infiltration and transport is rapid, with minimum water-rock interaction available to filter contaminants, and surface watersheds and ground-water basins do not coincide.

Parameters needed to further refine and expand the existing conceptual model were identified for this study. A series of wells and springs (8 demonstration projects) that transect the study area were selected and monitored using automated data loggers continuously for a period of one year. The objective of this monitoring was to establish temporal and spatial trends in hydrologic budget fluxes at a site-specific scale.

Currently, stage data from the springs is being converted into discharge values using established stage-rating curves. Storm hydrograph recession limb analysis of discharge data from each spring will be performed to determine aquifer storage (S), continuum transmissivity (T), and hydraulic conductivity (K). Spring basins integrate flow within a watershed, and S, T, and K values from the recession analyses of the springs will provide valuable information concerning differences between high and low flow regimes for the epikarst and prheatic zones.

Preliminary results indicate a wider range of responses and a more complex system than previously realized. Recharge and ground-water flow occurs along discrete pathways, some of which can be small and of limited extent; nonetheless, these flow paths are capable of transmitting significant quantities of water.