The historical potentiometric-surface map of the Edwards-Trinity aquifer system and contiguous hydraulically connected units is based on 1,789 water-level (or pressure-head) measurements made in wells between December 1915 and November 1969. The mapped data reflect a wide range of rainfall conditions. On the basis of interpretations of historical climatologic data by the National Oceanic and Atmospheric Administration, near- normal rainfall conditions preceded 55 percent of the measurements. Moderately dry conditions preceded 20 percent of the measurements; moderately wet conditions preceded 22 percent of the measurements; very dry conditions preceded less than 1 percent; and very wet conditions preceded 3 percent. The historical potentiometric-surface map represents general predevelopment conditions because negligible ground-water withdrawals existed in most areas when the water-level measurements used to construct the map were made. However, in Bexar, Reeves, Pecos, Reagan, and Upton Counties, early withdrawals caused declines in water levels that are reflected in water-level features shown on the map. Topographic relief and stream or spring drainage are two major factors affecting the configuration of the historical potentiometric surface. The strong influence of stream or spring drainage on the potentiometric surface shows that the regional direction of ground-water movement is largely dictated by the locations of major discharge feature. a
Additional publication details
USGS Numbered Series
Historical potentiometric surface of the Edwards-Trinity aquifer system and contiguous hydraulically connected units, west-central Texas
Water-Resources Investigations Report
1 map : col. ; 58 x 91 cm. + 2 data sheets (each 66 x 92 cm.), folded in envelope 31 x 24 cm.