REGIONAL GROUNDWATER FLOW MODEL OF THE OZARK PLATEAUS AQUIFER SYSTEM, NORTHWESTERN ARKANSAS, SOUTHEASTERN KANSAS, SOUTHWESTERN MISSOURI, AND NORTHEASTERN OKLAHOMA

To characterize groundwater flow within the Ozark Plateaus aquifer system, a regional groundwater flow model was developed using MODFLOW 2000 for a model area covering 7,340 square miles for parts of Arkansas, Kansas, Missouri, and Oklahoma. Vertically the model is divided into five units. From top to bottom these units of variable thickness are: the Western Interior Plains confining unit, the Springfield Plateau aquifer, the Ozark confining unit, the Ozark aquifer, and the St. Francois confining unit. Water-use data were compiled for the period 1960 to 2006, with the most complete data sets available for the period 1985 to 2006. In 2006, total water use from the Ozark aquifer for Missouri was 87 percent (8,531,520 cubic feet per day) of the total pumped from the Ozark aquifer, with Kansas at 7 percent (727,452 cubic feet per day), and Oklahoma at 6 percent (551,408 cubic feet per day); water use for Arkansas within the model area was minor. Water use in the model from the Springfield Plateau aquifer in 2005 was specified from reported and estimated values as 569,047 cubic feet per day. Calibration of the model was made against average water-level altitudes in the Ozark aquifer for the period 1980 to 1989 and against water-level altitudes obtained in 2006 for the Springfield Plateau and Ozark aquifers. Mean-absolute error between simulated and observed water-level altitudes in 2006 was 41.0 feet for the Springfield Plateau aquifer and 56.5 feet for the Ozark aquifer, compared to ranges in observed water-level altitudes of 845.2 and 442 feet respectively for the two aquifers. Groundwater flow within the model occurs generally from the highlands of the Springfield Plateau in southwestern Missouri toward the west, with localized flow occurring towards rivers and pumping centers including the five largest pumping centers near Joplin, Missouri, Carthage, Missouri, Noel, Missouri, Pittsburg, Kansas, and Miami, Oklahoma. Hypothetical scenarios involving various increases in groundwater pumping rates were analyzed with the calibrated groundwater flow model to assess changes in the flow system from 2007 to the year 2057.