Historic Flooding in Northern , September 16–22, 2009 A primary mission of the U.S. Geological Survey (USGS) is the measurement and documentation of the magnitude and extent of hydrologic hazards, such as , droughts, and hurricane storm surge. USGS personnel were deployed to document historic, widespread flooding that occurred throughout the metropolitan­ area and northwestern Georgia in the early fall of 2009. The floods were created by prolonged rainfall that occurred during Measuring Sweetwater Creek September 16–22, 2009, with an floodflow over Interstate 20 especially intense period of rainfall near Atlanta, Georgia. Photo during the late evening of September 20. by Alan M. Cressler, USGS. The National Weather Service (NWS) reported that the southeastern United States had above-normal precipitation at many USGS streamgages across the day. Hardest hit was the Basin from August into early September, result- region. Particularly hard hit was the in Douglas County, where floodwaters ing in saturated soil conditions making Basin, west of rose 12 ft above USGS streamgage the region extremely prone. Precip­ Metropolitan Atlanta. At USGS gaging 02337410. The Dog River crested at a itation totals were the sixth highest on station 02336000 on the Chattahoochee stage of 33.83 ft with a streamflow esti- record for the month of September for the River at Atlanta, Georgia, a peak flow mate of 59,900 ft3/s, which was almost region (National Weather Service, 2010). of 40,900 cubic feet per second (ft3/s) six times the 100-year flood. Upstream Monetary losses reported from and a peak stage of 28.12 feet (ft) were from Atlanta, Lake Sidney Lanier rose this flood were nearly $220 million in recorded on September 21. This was the almost 4 ft in a 48-hour period following flood-damage claims, with 17 counties highest stage in 81 years of continuous the storm and is credited for preventing declared Federal disaster areas. Eleven record at the gage. The September 22 record flood levels in Atlanta (James fatalities were attributed to this flood, peak flow represented between a 1- and Hathorn, U.S. Army Corps of Engineers, with many of them occurring during early 0.5-percent annual exceedance prob- oral commun., November 6, 2009). morning hours when drivers attempted to ability (100- to 200-year) flood. Station Significant flooding occurred in cross flooded roads. Significant damage 02337000 on Sweetwater Creek near the headwaters of the to hundreds of roads and bridges across Austell, Georgia, recorded a stage of Basin to the east of Atlanta. At USGS the region also severely impacted traffic 30.82 ft with a peak flow of 31,500 ft3/s, station 02207120 on the conditions for months after the event which resulted in an exceedance prob- at GA 124, near Lithonia, Georgia, the (National Weather Service, 2010). ability much greater than the 0.2-percent highest ever peak stage determined from The September 2009 flooding (500-year) flood level and caused the surveys was 27.47 ft on September 22, brought the highest levels ever recorded closure of Interstate 20 for more than a with a peak flow of 16,500 ft3/s.

Water flowing over the road from Allatoona Creek at Stilesboro Road near Acworth, Cobb County, Georgia, September 21, 2009. Photo by Andrew E. Knaak, USGS.

U.S. Department of the Interior Fact Sheet 2010–3061 U.S. Geological Survey July 2010 EXPLANATION 02398000 02392780 Little River at GA 5 02335815 Chattahoochee River 02335450 Chattahoochee River 02335000 Chattahoochee River Streamgage number and site name at Summerville, GA near Woodstock, GA below Morgan Falls Dam above Roswell, GA near Norcross, GA 100,000 100,000 100,000 100,000 100,000 100,000 1919 1919 Historic peak of record (water year) 1990 1 percent 2009 peak based 10,000 annual on floodmarks 10,000 10,000 exceedance 2007 10,000 10,000 probability 2004 1,000 Discrete 1,000 1,000 10,000 discharge measurement 1,000 1,000 100 Flood waters 100 100 destroyed gage Discharge, in cubic feet per second 10 10 10 1,000 100 100 19 20 21 22 23 24 19 20 21 22 23 24 19 20 21 22 23 24 19 20 21 22 23 24 19 20 21 22 23 24 19 20 21 22 23 24 September 2009 85° 84° DADE TOWNS CATOOSA FANNIN 02336000 Chattahoochee River 02336490 Chattahoochee River 02337000 Sweetwater Creek 02392975 at Shallowford RABUN Map at Atlanta, GA at GA 280 near Atlanta, GA near Austell, GA Road near Woodstock, GA area 100,000 100,000 1919 100,000 100,000 MURRAY UNION GEORGIA WALKER WHITFIELD GILMER

10,000 2005 HABERSHAM 1961 WHITE 10,000 2005 LUMPKIN 1,000 STEPHENS CHATTOOGA GORDON 83° 10,000 10,000 02398000 DAWSON PICKENS 100 1,000 BANKS FRANKLIN CHEROKEE 10 HART FLOYD BARTOW FORSYTH HALL 1,000 1,000 100 1 19 20 21 22 23 24 19 20 21 22 23 24 19 20 21 22 23 24 19 20 21 22 23 24 JACKSON 02392780 MADISON 02392975 ELBERT 02392950 34° POLK 02335450 02207120 Yellow River at GA 124 02393377 CLARKE 02337410 Dog River at GA 5 BARROW near Lithonia, GA 02393419 COBB 02335000 near Fairplay, GA 02337170 Chattahoochee River PAULDING 02335815 100,000 100,000 02336000 OGLETHORPE near Fairburn, GA 02336870 GWINNETT 100,000 1919 02336840 OCONEE HARALSON WALTON WILKES 02336490 02207120 LINCOLN 02337000 02207220 10,000 10,000 DOUGLAS DE KALB 2005 1982 02337410

CARROLL 02337170 CLAYTON 02207335 ROCKDALE MCDUFFIE FULTON TALIAFERRO 10,000 02337500 NEWTON GREENE COLUMBIA 1,000 1,000 MORGAN 02338000 HENRY FAYETTE WARREN HEARD COWETA PUTNAM 100 100 JASPER 19 20 21 22 23 24 19 20 21 22 23 24 SPALDING BUTTS HANCOCK 1,000 19 20 21 22 23 24 Fall Line 02207220 Yellow River at Pleasant Hill Road near Lithonia, GA 02337500 Snake Creek MERIWETHER PIKE LAMAR BALDWIN 100,000 near Whitesburg, GA JONES WASHINGTON 100,000 33° TROUP MONROE 02207335 Yellow River at Gees 02338000 Chattahoochee River Mill Road near Milstead, GA near Whitesburg, GA 100,000 100,000 10,000 10,000 1919 UPSON 2005 1961 BIBB CRAWFORD HARRIS EXPLANATION 1,000 TALBOT River basin 1,000 TAYLOR Chattahoochee Middle Tennessee– 10,000 10,000 2005 100 MUSCOGEE Flint Hiwassee Altamaha Upper Tennessee 100 0 20 40 MILES 19 20 21 22 23 24 10 Savannah Coosa–Tallapoosa 19 20 21 22 23 24 Guntersville Lake 0 20 40 KILOMETERS Ogeechee 1,000 19 20 21 22 23 24 1,000 Base modified from U.S. Geological Survey 19 20 21 22 23 24 1:100:000-scale digital files USGS streamgaging station

Streamgaging station—Sites in red exceeded 2 percent annual exceedance probability. See table 16th The Coosa and Tennessee River Basins operation by floodwaters. USGS field personnel also were flooded in many locations. The USGS performed flood measurements to extend - streamgages on Allatoona, Noonday, and Butler flow ratings that allowed for more accurate NWS Creeks—all to Allatoona Lake— forecasts. All 20 streamgages were restored to recorded peak flows with magnitudes far greater operational status within 5 days, however. than 0.2-percent (500-year) floods. Although these Lessons learned from this flood include the flows caused Allatoona Lake to rise to more than need for more effective communication of the latest 13 ft above the full-pool level, the dam still saved river information by Federal agencies with flood- the downstream community of Rome, Georgia threatened communities. Communicating the flood 17th (James Hathorn, U.S. Army Corps of Engineers, threat in an easy, accessible manner would have oral commun., November 6, 2009). helped emergency managers and the public greatly During this historic flood, more than during this flood. In response, the USGS developed 50 USGS streamgages throughout WaterAlert (http://water.usgs.gov/wateralert) to recorded flows above the highest ever measured, send notifications of flood events by way of text and 20 USGS streamgages were knocked out of and e-mail. Also in development are real-time flood-inundation maps to give the hydrograph EXPLANATION spatial context by way of a map-based product. Observed daily precipitation, in inches 18th 5.0 2.0 0.5 References 10 4.0 1.5 0.25 National Weather Service, 2009, Advanced Hydrologic Predic- 8.0 3.0 1.0 0.10 tion Service—Precipitation: U.S. Department of Commerce, 6.0 2.5 0.75 0.01 National Oceanic and Atmospheric Administration, accessed 5.0 2.0 0.50 in January 2010 at http://water.weather.gov/precip/. Daily precipitation images for September 2009 from the NWS National Weather Service, 2010, Service Assessments— (2009). USGS raingages provide ground verification and Southeast United States Floods, September 18–23, 2009: calibration for the NWS radar system. The radar imagery Silver Spring, MD, U.S. Department of Commerce, National provides estimates of rainfall between the raingages to Oceanic and Atmospheric Administration, Office of Climate, better characterize the total rainfall for a watershed. Water, and Weather Services, accessed in May 2010 at http://www.weather.gov/os/assessments/pdfs/se_floods10.pdf . 19th Recorded flooding in September 2009 at selected USGS continuous-monitoring streamgages in northern Georgia. Date of Peak Annual Station Peak peak flow exceedance identi- Station name gage (September (cubic feet probability fication height 2009) per second) (percent) 02207120 Yellow River at GA 124, near Lithonia, GA 22 16,500 27.47 1 to 0.5 02207220 Yellow River at Pleasant Hill Road, 22 22,900 25.54 0.5 to 0.2 near Lithonia, GA 02207335 Yellow River at Gees Mill Road, 22 20,800 22.54 2 to 1 20th near Milstead, GA 02335000 Chattahoochee River near Norcross, GA 21 14,900 14.51 Regulated 02335450 Chattahoochee River above Roswell, GA 21 21,100 11.96 Regulated 02335815 Chattahoochee River below 21 35,500 827.01 Regulated Morgan Falls Dam, GA 02336000 Chattahoochee River at Atlanta, GA 21 40,900 28.12 Regulated 02336490 Chattahoochee River at GA 280, 21 42,300 35.98 Regulated near Atlanta, GA 02336840 Sweetwater Creek at Brownsville Road, 21 30,000 31.40 Exceeded 0.2 21st Powder Springs, GA 02336870 Powder Springs Creek near Powder Springs, GA 21 8,940 19.91 Exceeded 0.2 02337000 Sweetwater Creek near Austell, GA 22 31,500 30.82 Exceeded 0.2 02337170 Chattahoochee River near Fairburn, GA 22 63,900 30.65 1 to 0.5 02337410 Dog River at GA 5, near Fairplay, GA 21 59,900 33.83 Exceeded 0.2 02337500 Snake Creek near Whitesburg, GA 21 13,500 19.42 Exceeded 0.2 02338000 Chattahoochee River near Whitesburg, GA 23 60,600 29.74 Regulated 02392780 Little River at GA 5, near Woodstock, GA 21 16,100 20.80 1 to 0.5 22nd 02392950 Noonday Creek at Hawkins Store Rd, 21 11,900 17.28 Exceeded 0.2 near Woodstock, GA 02392975 Noonday Creek at Shallowford Road, 21 11,400 19.66 Exceeded 0.2 near Woodstock, GA 02393377 Butler Creek at Mack Dobbs Road, 21 6,760 14.27 Exceeded 0.2 near Kennesaw, GA 02393419 Allatoona Creek at Stilesboro Rd, 21 16,600 23.90 Exceeded 0.2 near Acworth, GA 02398000 Chattooga River at Summerville, GA 21 23,500 21.19 2

By Brian E. McCallum and Anthony J. Gotvald. For more information, contact the Georgia Water Science Center at 770-903-9100 or http://ga.water.usgs.gov.