Simulation of ground-water flow in the Mississippi River Valley alluvial aquifer in eastern Arkansas

Abstract

The U.S. Geological Survey's participation in a study of the water resources in eastern Arkansas involved the development and calibration of a digital ground-water flow model of the Mississippi River Valley alluvial aquifer and the use of that model to evaluate the effects of future pumping on the saturated thickness of the aquifer. The study was prompted by the growing concern about significant water-level declines in the alluvial aquifer north of the Arkansas River.Thickness of alluvial sediments in the study area ranges from 125 to 200 feet and averages about 150 feet. The most permeable material lies in the lower part of the sediments and averages about 100 feet in thickness. Hydraulic conductivity of the aquifer ranges from about 120 to about 390 feet/day.Recharge to the aquifer occurs mainly by percolation through the overlying confining layer in interstream areas and by seepage through riverbeds. A small amount of recharge also comes from the sediments underlying the alluvium.Recharge rates in interstream areas range from less than 1 to as much as 10 inches in areas where recharge from underlying sediments is substantial.Digital model simulations were made to represent flow in the aquifer and to quantify flow into and out of the system. The dynamic ground-water system was simulated by using seven stress periods between 1917 and 1987. Pumpage used in the simulation ranged from 86,950,000 to 420,970,000 cubic feet per day. Pumpage was distributed uniformly over each county after eliminating areas where the predominant land use precluded ground-water withdrawals.-4 Storage coefficient values of 0.3 and 1x10 for unconfined and confined aquifer conditions, respectively, were used in the simulations. measures were not in place and 258 (1,486,080 acres) of the active cells with conservation measures in place.

Updated estimates of water budget components for the Mississippi Embayment Region using a soil-water-balance model, 2000–2020

“…Pumping from this aquifer and underlying aquifers supplies water for the irrigation of crops, aquaculture, drinking water for urban areas, industrial supply, and other uses (Clark and others, 2011;Lovelace and others, 2020). The heavy use of this aquifer has caused substantial groundwater level declines in the alluvial plain of Arkansas and Mississippi, which has motivated a large number of hydrologic studies by the USGS aimed at understanding groundwater movement in the system of aquifers in the area and the potential effect of increasing or reducing pumping on groundwater supply and availability (Boswell and others, 1968;Cushing and others, 1970;Broom and Reed, 1973;Brahana and Mesko, 1988;Ackerman, 1989Ackerman, , 1996Mahon and Ludwig, 1990;Sumner and Wasson, 1990;Arthur and Taylor, 1998;Arthur, 2001;Brahana and Broshears, 2001;Mahon and Poynter, 1993;McKee and Clark, 2003;Reed, 2003;Stanton and Clark, 2003;Kresse and Clark, 2008;Clark and Hart, 2009;others, 2011, 2013).…”