The alluvial aquifer near Carrollton, Kentucky, lies in a valley eroded by glacial meltwater that was later part filled with outwash sand and gravel deposits. The aquifer is unconfined, and ground water flows from the adjacent bedrock-valley wall toward the Ohio River and ground-water withdrawal wells. Ground-water-level and Ohio River stage data indicate the alluvial aquifer was at or near steady-state condition in November 1995.
A two-dimensional, steady-state ground-water-flow model was developed to estimate the hydraulic properties, the rate of recharge, and the contributing areas to discharge boundaries for the Ohio River alluvial aquifer at Carrollton and the surrounding area. Results from previous investigations, available hydrogeologic data, and observations of water levels from area ground-water wells were compiled to conceptualize the ground-water-flow system and construct the numerical model. Ground water enters the modeled area by induced infiltration from the Ohio River and smaller streams, flow from the bedrock-valley wall, and infiltration of precipitation. Ground water exits the modeled area primarily through withdrawal wells and flow to the Ohio River. A sensitivity analysis of the model indicates that it is most sensitive to changes in the stage of the Ohio River and conductance values for the riverbed material. A particle-tracking simulation was used to delineate recharge and discharge boundaries of the flow system and contributing areas for withdrawal wells, and to estimate time of travel through the flow system.