The 100-Year Flood
Epic Flooding in Georgia, 2009
Metropolitan Atlanta—September 2009 Floods
- The epic floods experienced in the Atlanta area in September 2009 were extremely rare. Eighteen streamgages in the Metropolitan Atlanta area had flood magnitudes much greater than the estimated 0.2-percent (500-year) annual exceedance probability.
- The Federal Emergency Management Agency (FEMA) reported that 23 counties in Georgia were declared disaster areas due to this flood and that 16,981 homes and 3,482 businesses were affected by floodwaters. Ten lives were lost in the flood.
- The total estimated damages exceed $193 million (H.E. Longenecker, Federal Emergency Management Agency, written commun., November 2009).
- On Sweetwater Creek near Austell, Ga., just north of Interstate 20, the peak stage was more than 6 feet higher than the estimated peak stage of the 0.2-percent (500-year) flood. Flood magnitudes in Cobb County on Sweetwater, Butler, and Powder Springs Creeks greatly exceeded the estimated 0.2-percent (500-year) floods for these streams.
- In Douglas County, the Dog River at Ga. Highway 5 near Fairplay had a peak stage nearly 20 feet higher than the estimated peak stage of the 0.2-percent (500-year) flood.
- On the Chattahoochee River, the U.S. Geological Survey (USGS) gage at Vinings reached the highest level recorded in the past 81 years. Gwinnett, De Kalb, Fulton, and Rockdale Counties also had record flooding.
USGS Role During the Floods
- One of the primary missions of the USGS is the measurement and documentation of the magnitude and extent of hydrologic hazards, such as floods, droughts, and hurricane storm surge.
- In Georgia, the USGS maintains a network of more than 300 streamgages that provide data in real time via the Internet. Data from these stream gages are used by local, State, and Federal officials for numerous purposes, including public safety, National Weather Service (NWS) flood forecasting, and to aid emergency management officials in making informed decisions before, during, and after flood events.
- During these two flood events, USGS personnel made more than 100 discrete flood measurements, performed extensive ongoing analysis of ratings and flood frequency, collected water-quality samples in flooded areas, and provided routing briefings to USGS Headquarters, NWS, local government officials, and the press.