USING GIS APPLICATIONS TO MODEL GROUNDWATER USAGE OF IRRIGATION WELLS IN WESTERN TENNESSEE (USA)

Tennessee Water Well Driller Reports document the installation of 1,174 irrigation wells for row crop production between June 1995 and March 2014 in eighteen west Tennessee counties with the greatest proliferation of wells occurring after the droughts in 2007 and 2008. Location information (latitude, longitude), well completion date, well depth, well diameter, well pump output (gallons per minute; GPM), and other information from the driller reports were input into a GIS database using ArcGIS. Using a Digital Elevation Model and the published raster surfaces from the 2008 Mississippi Embayment Regional Aquifer Study (MERAS), the depth and aquifers of withdrawal were determined by calculating the difference between surface elevation and total well depth and comparing this value to the altitudes of the hydrologic units below the location of the well. Analyses of withdrawal rates were performed by creating a raster map of well pump GPMs using an inverse distance weighted (IDW) interpolation. Aquifers primarily targeted by these irrigation wells include the Mississippi River Valley alluvial and the middle Claiborne (“Memphis Sand”) aquifers and to a lesser extent the upper Claiborne, middle Wilcox, and lower Wilcox aquifers. The middle Claiborne confining unit is also tapped across eight west Tennessee counties. In Lake, Obion, Dyer, and Lauderdale counties, irrigation wells (n = 110) tapping the Mississippi River Valley alluvial aquifer produce groundwater at rates of 2,000-4,000 GPM. Irrigation wells in the other west Tennessee counties tap into the upper Claiborne, middle Claiborne (“Memphis Sand”), middle Wilcox and lower Wilcox aquifers and the middle Claiborne confining unit at lower production rates of 500-1,000 GPM. This study will help assess the impact of irrigation on groundwater resource usage in west Tennessee.