ABSTRACT

As part of the U.S. Department of the Interior sustainable water strategy, WaterSMART, the U.S. Geological Survey documented hydrologic and water-quality conditions in the lower Apalachicola–Chattahoochee–Flint and western and central Aucilla–Suwanee–Ochlockonee River basins in Alabama, Florida, and Georgia during low-flow conditions in July 2011. Moderate-drought conditions prevailed in this area during early 2011 and worsened to exceptional by June, with cumulative rainfall departures from the 1981–2010 climate normals registering deficits ranging from 17 to 27 inches. As a result, groundwater levels and stream discharges measured below median daily levels throughout most of 2011. Water-quality field properties including temperature, dissolved oxygen, specific conductance, and pH were measured at selected surface-water sites.

Record-low groundwater levels measured in 12 of 43 surficial aquifer wells and 128 of 312 Upper Floridan aquifer wells during July 2011 underscored the severity of drought conditions in the study area. Most wells recorded groundwater levels below the median daily statistic, and 7 surficial aquifer wells were dry.

Groundwater-level measurements taken in July 2011 were used to determine the potentiometric surface of the Upper Floridan aquifer. Groundwater generally flows to the south and toward streams except in reaches where streams discharge to the aquifer. The degree of connection between the Upper Floridan aquifer and streams decreases east of the Flint River where thick overburden hydraulically separates the aquifer from stream interaction. Hydraulic separation of the Upper Floridan aquifer from streams located east of the Flint River is shown by stream-stage altitudes that differ from groundwater levels measured in close proximity to streams.

Most streams located in the study area during 2011 exhibited below normal flows (streamflows less than the 25th percentile), substantiating the severity of drought conditions that year. Streamflow and springflow measured at 202 sites along 2,122 stream miles during July 20–24, 2011, identified about 286 miles of losing streams, about 1,230 miles of gaining streams, and about 606 miles of streams with no flow.

Water-quality field properties measured at 123 stream and 5 spring sites during July 2011 yielded water temperatures ranging from 20.6 to 31.6 degrees Celsius, dissolved oxygen ranging from 0.47 to 9.98 milligrams per liter, specific conductance ranging from 13 to 834 microsiemens per centimeter at 25 degrees Celsius, and pH ranging from 3.6 to 8.03.

Revised October 19, 2012

First posted September 10, 2012