Extreme drought to extreme floods: summary of hydrologic conditions in Georgia, 2009

Abstract

The U.S. Geological Survey (USGS) Georgia Water Science Center (GAWSC) maintains a long-term hydrologic monitoring network of more than 317 real-time streamgages, more than 180 groundwater wells of which 31 are real-time, and 10 lake-level monitoring stations. One of the many benefits of data collected from this monitoring network is that analysis of the data provides an overview of the hydrologic conditions of rivers, creeks, reservoirs, and aquifers in Georgia. HYDROLOGIC CONDITIONS Hydrologic conditions are determined by statistical analysis of data collected during the current water year1 (WY) and comparison of the results to historical data collected at longterm stations. During the 2009 WY, Georgia experienced a dramatic change from drought conditions to above-normal streamflows. Maps A–D (Fig. 1) indicate that during the first half of the 2009 WY, most streams in Georgia had flows much below normal, but by the end of the year, the majority of Figure 1. These maps represent hydrologic conditions in the context of available historical data. The colors represent current 7-day average streamflow as a percentile class of long-term averages. Only stations having at least 30 years of record were used (U.S. Geological Survey, 2010b). Because of persistent drought conditions that began in spring 2006, streamflow conditions at the beginning of the 2009 WY in the State were “much below normal” (map A). Steady rainfall and spring flooding in south Georgia brought much-needed relief, and 7-day average stream flow conditions improved from “below normal” to “above normal” (maps B and C). By September 30, 2009, the end of the water year, the 7-day average streamflows throughout most of Georgia were “much above normal” (map D). A. Oct. 1, 2008 B. Mar. 1, 2009 C. June 1, 2009 D. Sept. 30, 2009 GEORGIA streams had flows much above normal. At the start of the 2009 WY, new historic minimum streamflows were recorded at several streamgages with 20 or more years of record, and reservoirs approached historic low elevations. South Georgia received drought relief as a result of historic flooding from March 27–April 3, 2009. North Georgia experienced historic flooding during September 16–22, 2009. During these flood events, GAWSC hydrographers verified peak streamflows and flood levels, and this information was shared with Federal, State, and local agencies for use in protecting life and property. New record peak flows were observed in many creeks and rivers throughout the State during these epic floods, and reservoir and lake elevations approached full pool. Extreme hydrologic conditions, both drought and floods, in the 2009 WY emphasizes the need for accurate, timely data to help make informed decisions by state and local authorities regarding the management and conservation of Georgia’s water resources for the protection of life. On June 10, 2009, Governor Perdue met with the State Drought Response Committee and announced that the Environmental Protection Division issued a non-drought schedule for outdoor water use for the first time since June 2006 (State of Georgia, 2010). This announcement was made as a result of substantial rainfalls and improved water supplies in Georgia. Under a non-drought schedule, household outdoor water use is allowed 3 days a week. Much above normal, > 90 Much below normal < 10 Above normal, 76 to 90 Normal, 25 to 75 Below normal, 10 to 24 EXPLANATION Percentile classes 1 Water year is the period October 1 through September 30 and is designated by the year in which it ends. For example, the 2009 water year began on October 1, 2008, and ended on September 30, 2009. 1 10 100 1,000 10,000 100,000 J F M A M J J A S O N D 2008 2009 Da ily d is ch ar ge , in c ub ic fe et p er s ec on d 7da y av er ag e di sc ha rg e, in c ub ic fe et p er s ec on d 02337040 Sweetwater Creek Below Austell, Georgia