Layered GeoPDF 7.5 Minute Quadrangle Map. Layers of geospatial data include orthoimagery, roads, grids, geographic names, elevation contours, hydrography, and other selected map features.

The Sparta aquifer is the principal source of ground water in north-central Louisiana. In 1985, the aquifer was extensively pumped for public supply (25 Mgal/d) and industrial use (29 Mgal/d and 7 Mgal/d for 1989). More than 100 public supply systems, in 8 parishes, contain water from the Sparta aquifer. Large industrial pumpage from the Sparta aquifer began in 1922 at Bastrop (Sanford, 1973a, p. 60) and in about 1923 at West Monroe. Water levels in wells in the Sparta aquifer have been declining in these arease and in other parts of north-central Louisiana since the early 1920's, when industries began withdrawing large amounts of water. However, in Morehouse Parish the water levels in wells have been recovering since 1982 as a result of a 5 Mgal/d reduction in pumpage at Bastrop (J.K. Lovelace, U.S. Geological Survey, written commun., 1989). Additional knowledge about ground-water flow and the effects of withdrawals on the Sparta aquifer is needed for assessment of ground-water development potential and protection of the resource. Potentiometric contour maps are used to determine direction of ground-water flow, ground-water gradients, and the effects of pumping on an aquifer system. The rate of ground-water movement can be estimated when the hydraulic conductivity of an aquifer is known. This report presents data and maps that illustrate the potentiometric surface and water-level changes for the Sparta aquifer and is the third in a series of map reports that show potentiometric surface and water-level changes of aquifers in Louisiana (Fendick, 1989; Fendick and Nyman, 1987). These maps were prepared in cooperation with the Louisiana Department of Transportation and Development. Reports prepared as part of previous studies of northern Louisiana with emphasis on the Sparta aquifer are included in the Selected References. These maps show the potentiometric surface in the spring of 1989 and water-level changes from 1980 to 1989 for the Sparta aquifer. The regional potentiometric surface of the Sparta aquifer, based on water-level measurements made during May through June 1989, is shown in figure 1. Ground-water flow directions are normal to the contours, from higher to lower head. Water-level changes in wells in the Sparta aquifer from May 1980 to May 1989 are shown in figure 2. Three hydrographs (figs. 3-5) show general water-level trends for periods 1920-89, 1946-89, and 1970-89.

Aeromagnetic data were collected along flight lines by instruments in an aircraft that recorded magnetic-field values and locations. In the earlier days of surveying, the only way to represent this data was to generate an analog map with contour lines. This dataset is a representation of the digitized contour lines either by following the lines or by choosing the intersection of the contour and flight-line to create a value of the magnetic field. The values presented are latitude, longitude, and map magnetic-field values.