Stream base flow and potentiometric surface of the Upper Floridan aquifer in south-Central and southwestern Georgia, November 2008

An investigation to document groundwater levels and stream base flow in the lower Chattahoochee-Flint and western and central Aucilla-Suwanee-Ochlockonee River basins during low-flow conditions was conducted by the U.S. Geological Survey in November 2008. During most of 2008, moderate to severe drought conditions prevailed throughout southwestern Georgia. Groundwater levels were below median daily levels throughout most of 2008; however, in some wells, groundwater levels rose to median daily levels by November. Discharge in most of the streams in the study area also had risen to median levels by November.

The potentiometric surface of the Upper Floridan aquifer was constructed from water-level measurements collected in 21 counties from 376 wells during November 1-10, 2008. The potentiometric surface indicates that groundwater in the study area generally flows to the south and toward streams except in reaches discharging to the Upper Floridan aquifer. The degree of connection between the Upper Floridan aquifer and streams decreases east of the Flint River where the overburden is thicker. Decreased connectivity between ground and surface water is evident from the stream-stage altitudes measured in November 2008 east of the Flint River, which are not similar to water-level altitudes measured in the Upper Floridan aquifer.

Stream-stage measurements were collected at 111 sites-26 U.S. Geological Survey streamgaging sites and 85 additional synoptic sites without gages. Streamflow measurements were made at 87 of the sites during November 2008 and were used to estimate base flow. The measurements indicate that stream reaches range from losing up to 10 cubic feet per second to gaining up to 4,559 cubic feet per second; five stream reaches were determined to be losing stream reaches. Of the 11 stream reaches in the Alapaha River subbasin, 7 were dry when measured in November 2008.