PLEISTOCENE AGED RIVER DEPOSITS AND THEIR EFFECT ON THE ALLUVIAL AQUIFER AT DARDANELLE, ARKANSAS

The alluvial aquifer at Dardanelle, Arkansas is a rich source of quality groundwater used for industrial, domestic and irrigational purposes. During the Pleistocene, the lowering of sea level around the world caused the Arkansas River to down cut its channel in an effort to reach a baseline with the ocean. This down cutting left behind numerous original point bar and river channel deposits as terrace deposits. At the end of the Pleistocene, as sea level rose, the river system's rate of flow decreased causing it to unload vast amounts of alluvial sediments. These alluvial sediments are what became the present day aquifer. The older terrace deposits left behind during the Pleistocene are located along the outside edges of the present day floodplain. These terrace deposits represent potential areas of both groundwater recharge, and point source contamination of the alluvial aquifer. The research reported here has included mapping of these deposits within a two-kilometer long stretch of land west of Dardanelle, Arkansas, as well as developing working hypotheses of their influence on the present day aquifer. The influence of these terrace deposits is important to understanding the complex nature of the groundwater system in Dardanelle. With further funding we will be using drilling and/or ground penetrating radar to map the depth of these terrace deposits, in order to determine how much if any contact they actually have with the aquifer. These potential contact areas are of invaluable importance in construction of an accurate groundwater flow model of the aquifer for determining amounts of water available for future consumption and for assessing the aquifer's vulnerability to contamination.