Ozarkaquifer_2015waterlevelalt_contours

The regional Ozark aquifer potentiometric-surface map shows the altitude at which the water level would have risen in tightly cased wells and represents conditions during the period from November 2014 through January 2015. Water levels were measured during this period to ensure that wells had adequate time to recover from previous summer pumping and prior to the start of the 2015 summer pumping season. Groundwater-level data from 178 wells cased completely in and open to the Ozark aquifer are available from the USGS National Water Information System (NWIS; data available at http:// waterdata.usgs.gov/nwis). Streams and springs in the study area represent the intersection of the groundwater table with land surface; these features were used in the construction of the potentiometric-surface map. In Arkansas and Missouri, where the Ozark aquifer crops out, altitudes of select gaining stream reaches, compiled from previous reports on gaining and losing streams (data available at http://dx.doi.org/10.5066/F7W9577Q) and select springs (data available at ftp://msdis.missouri.edu/pub/Inland_Water_Resources/MO_2010_ Springs_shp.zip), were calculated from 10-meter digital elevation data (Knierim and others, 2015; Missouri Department of Natural Resources and others, 2010). After collecting and processing the data, a potentiometric surface was generated by using the interpolation method TopotoRaster in ArcMap. This tool is specifically designed for the creation of hydrologically correct digital elevation models while imposing constraints that ensure a connected drainage structure and a correct representation of the surface from the provided contour data (Esri, 2011). Once the raster surface was created, 100-ft contours were generated by using Contour (Spatial Analyst), which is a spatial analyst tool (available through ArcGIS Spatial Analyst Toolbox) that creates a linefeature class of contours (isolines) from the raster surface (Esri, 2008). Contours were manually adjusted based on topographical influence, a comparison with the regional map of Imes and Emmett (1994), and data point water-level altitudes to more accurately represent the potentiometric surface.