APPLICATION OF CONTINUOUS MONITORING OF WATER LEVELS AND TEMPERATURES OF WELLS AND SPRINGS AT THE SAVOY EXPERIMENTAL WATERSHED TO ELUCIDATE MULTICOMPONENT MIXING IN A SHALLOW, MANTLED-KARST AQUIFER

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 site in which flow and transport are heterogeneous and anisotropic and may be studied in a well-characterized setting. In September 2007, continuous monitoring of water levels and temperatures at SEW was reinitiated using data loggers and a series of weirs and wells. These measurements define hydrologic-budget parameters needed for development of a revised conceptual model. Data loggers were placed along a 4 - well transect, in one epikarst spring, and in two major springs forming an overflow/underflow system in the phreatic zone located at the distal end of a flow path. Weather data were collected for precipitation, air temperature, and barometric pressure, needed for compensation calculations. 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 controlled primary ground-water flow, with structural features forming a secondary control. Initial data, from period of record 10-23-07 to 01-02-08, reveal that the system is much more complex than preliminary models show. Thermal data are highly variable, ranging from shallow flow zones reflecting surface signatures, through intermediate, more insulated zones with delayed and subdued responses to surface processes, to deep zones that are decoupled from the surface and are equilibrated with local geothermal regime. Water levels are equally variable where stage increases and recessions are nonlinear and vary spatially from station to station with precipitation events. During and following precipitation events, exponential water-level increases in some deep wells do not impact the thermal signature, suggesting that the fluids moving through the system are well mixed and had a long enough residence time to reach thermal equilibrium. These data suggest a more-than-three component model where zones of infiltration and mixing occur along discreet flow paths.