GROUND-WATER AND SURFACE-WATER INTERACTION BETWEEN THE SHALLOW, MANTLED CARBONATE AQUIFERS OF NORTHWEST ARKANSAS AND THE ILLINOIS RIVER NEAR THE SAVOY EXPERIMENTAL WATERSHED

Groundwater and surface water are a single, interconnected resource in most hydrogeologic settings, and no more so than in karst terranes, where the relationship is typically so great it represents the upper end of a fluvial continuum. Hydrogeology studies in karst environments require accurate budget terms. This study was conducted at the University of Arkansas through an NSF funded Research Experience for Undergraduates program. It attempts to characterize the river’s flow along 11 kilometers of the Illinois River in the vicinity of the Savoy Experimental Watershed (SEW) in Northwest Arkansas. The SEW is under development to determine the effect of livestock and farm waste on the groundwater of a mantled-karst environment. As the Illinois River flows past this site, the river gains a significant amount of water from Clear Creek as well as from seeps and springs, which flow through the surrounding mantled karst and exit into the river. This quantification of discharge to and from the river will allow for accurate modeling of groundwater and surface water runoff in the SEW. It will help further develop the water budget at the SEW and determine whether the Illinois contributes to the deep aquifer groundwater beneath the SEW, or whether it acts only as a regional hydraulic drain. The experiment will also help to constrain calculations related to tracer and contaminant studies at the SEW. The streams were gaged following USGS protocol utilizing a Teledyne Gurley pygmy meter, and v-notch weirs; the USGS Illinois River at Savoy, AR gage was used as a standard for verification of field equipment and protocol. The Illinois was gauged about once per kilometer while the tributaries were gaged where they joined the river. The study hypothesizes that some portions of the Illinois have a net loss, but that an overall gain along the 11 kilometer stretch exists. The study also attempts to determine the location of the springs and seeps along the banks of the river through the water chemistry, temperature and low-flow reconnaissance. The main field parameters tested were specific conductivity, pH and temperature. By comparing water data of the Illinois River and the incoming seeps and springs to the known chemistry of boreholes and shallow wells located in the SEW, it is hypothesized that the groundwater entering the Illinois River is of shallow origin.