Effects of fluctuating river-pool stages on ground-water levels in the adjacent alluvial aquifer in the lower Arkansas River, Arkansas

The U.S. Geological Survey conducted a study in cooperation with the U.S. Army Corps of Engineers to determine the effect of fluctuating the lower Arkansas River. A network of 41 wells was used to delineate 4 cross sections adjacent to river pools 2 and 5 of the McClellan-Kerr Arkansas River Navigation System to examine groundwater levels at various distances from the river. The hydraulic gradient of water levels in the alluvial aquifer along these cross sections indicates that the river is losing water to the adjacent aquifer. The effect on groundwater levels in the alluvial aquifer caused by pool-stage fluctuations was most pronounced at distances less than about 2 miles from the Arkansas River. At distances greater than about 2 miles, the changes in groundwater levels probably were the result of water levels rising in the aquifer since the heavy summer irrigation withdrawals have ceased. An equation useful for estimating the distribution of head change an aquifer in response to river-pool-stage changes, was applied to the study area to estimate the effect of a 1-foot rise in pool stage on water levels in the adjacent alluvial aquifer after equilibrium conditions have been established. The theoretical head change (rise) in the aquifer was estimated to range from 1-foot at the Arkansas River to 0.57 foot at a distance of 5 miles away from the river. (USGS)