Ground-Water Modeling Support

Several counties in eastern and southern Arkansas have been designated Critical Ground-Water Areas (areas where alluvial aquifer water levels dropped below 50 percent of the original saturated thickness or below the top of the Sparta Sand) by the Arkansas Natural Resources Commission. The expansion of the cones of depression and the consistent water-level declines indicate that ground-water withdrawals are occurring at a rate that is greater than the sustainable yield of the aquifer. This study utilizes and maintains ground-water flow models that were developed to assess effects of ground-water withdrawals on the alluvial and Sparta aquifers. The north alluvial ground-water flow model (north model) by Reed (2003) was developed to assist ground-water managers with assessing the impact of future stresses induced by ground-water withdrawals on ground-water levels. The north model had water-use data from 1997 as its most-recently compiled water-use dataset and water-level altitude data to 1998. To verify the performance of this model in simulating subsequent periods of water use and observed water levels, updates to this and other the models are required.

Map of North Alluvial aquifer modeling area.

The current ground-water modeling support study will verify the Reed (2003) model to 2005 conditions. Approximately 40,000 wells are represented in the north model, which covers an area of over 14,000 square miles. Water-use data from alluvial aquifer wells from 1997-2005 and water-level observation data beginning in 2000 will be compiled as observation data for model verification. Annual stress periods will be added to the model corresponding to the water-use data available beginning in 2000 through to 2005. To permit comparison with results presented by Reed (2003), the model will be run to 2049, assuming (a) fixed pumping rates at 2005 rates; and (b) pumping rate increases assuming pumping rate increases based on past trends by county. Differences in water levels between the model of Reed (2003) and the updated model will be presented for simulated water levels corresponding to 2049.

Publications
	Scientific Investigations Report 2009-5040 Validation of a Ground-Water Flow Model of the Mississippi River Valley Alluvial Aquifer Using Water-Level and Water-Use Data for 1998-2005 and Evaluation of Water-Use Scenarios, By Jonathan A. Gillip and John B. Czarnecki
	Scientific Investigations Report 2008-5138 Evaluation of Selected Model Constraints and Variables on Simulated Sustainable Yield from the Mississippi River Valley Alluvial Aquifer System in Arkansas, By John B. Czarnecki
	Scientific Investigations Report 2007-5030 Simulated Ground-Water Withdrawals by Cabot WaterWorks from the Mississippi River Valley Alluvial Aquifer, Lonoke County, Arkansas by John B. Czarnecki
	Scientific Investigations Report 2006-5275 Effects of Proposed Additional Ground-Water Withdrawals from the Mississippi River Valley Alluvial Aquifer on Water Levels in Lonoke County, Arkansas by John B. Czarnecki
	Water-Resources Investigations Report 2003-4109 Recalibration of a Ground-Water Flow Model of the Mississippi River Valley Alluvial Aquifer of Northeastern Arkansas, 1918-1998, with Simulations of Water Levels Caused by Projected Ground-Water Withdrawals, by Tom B. Reed