Catastrophic flooding impacted the Atlanta metropolitan area September 15-22, 2009, as a result of multiple days of prolonged rainfall. A combination of ample moisture from both the Atlantic Ocean and the Gulf of Mexico and topography enhancement produced heavy rains that fell faster than local watersheds could handle. At the height of the event, September 20-21, an estimated 10 to 20 inches of rain occurred in less than 24 hours. Historic flash flooding resulted, with flooded river basins remaining swollen for weeks. Numerous flood records were set, with some locations observing conditions exceeding the 0.2% chance of occurrence in a given year. The maximum 24-hour rainfall total for September 20-21, 2009, was 21.03 inches, observed at the Douglas County Water and Sewer Authority. The chance of any location in the Atlanta area receiving this amount of rainfall in any given 24-hour period is less than 0.01% annually. The epic flooding that occurred greatly impacted the community and economy. Initial property damage in Georgia was estimated at $250 million, but was eventually raised to $500 million. More than 20,000 homes, businesses and other buildings sustained major damage, including 16,981 residences. Unfortunately, 10 Georgia residents lost their lives during this event. Of those, 9 died during the overnight hours, and 8 died driving across flooded roads. Additionally, hundreds of people were rescued from their homes and vehicles. Portions of all major Atlanta-area interstates, including I-20, I-75 and I-85, were closed. The impact of the heavy rainfall to area creek and river systems lasted for weeks. There were 79 river gages that rose above flood stage, with 35% of those cresting above major flood stage. More than one third of the gages rose to never-before-seen levels. During the height of the event, 20 river gages went underwater and stopped reporting. In these cases high water marks were surveyed to determine the peak stage height. At Sweetwater Creek near Austell, Georgia, the new established record was 20 feet above flood stage and nine feet above the previous record crest. In Douglas County, the Dog River overtopped the USGS stream gage by 12 feet. In total, 28 new record crests were set, one of which was originally established in 1919. These swollen river basins resulted in damage to 21 Category One dams. The Chattahoochee River, the largest river in the region, measured water levels at a 500-year flood level. Seventeen counties in Georgia received Federal Disaster Declarations, the majority of which were in the Atlanta Metropolitan area. The clean-up and rebuild process continued into 2010. As of September 2010, there were more than 16,000 requests and inquiries for federal aid. Me and my family had just moved to a house in Douglasville at the time west of Atlanta one of the hardest hit areas during the flood was Douglas, Cobb, and Fulton Counties. The road I lived on washed out and many others across the county there was detours everywhere for months. I was in 4th grade at the time and school was closed for a long time. It is a weather event I'll never forget! The western side of the Interstate 285 crosses the Chattahoochee River. This section of the interstate was completely underwater for several days. Many of the roller coasters and rises at Six Flags Over Georgia were partly underwater, with at least 80% of The Great American Scram Machine submerged by the Chattahoochee River. Located along the Chattahoochee River in west Atlanta, the R.M. Clayton swage treament plant, the largest in the Southeast, was swamped with four feet of water as the river rose by twelve additional feet. Millions of gallons of untreated sewage were released into the rising waters. Other plants in Cobb and Gwinett counties experienced similar spills. Also located near the Chattahoochee, a Kellog copany food plant was flooded, resulting in the closure of the plant and a subsequent national shortage of frozen waffles.
Lake Lanier and Lake Allatoona
Lake Lanier rose quickly, while Lake Allatoona soared to more than ten feet or three meters over full pool, using its flood reserve capacity for the first time after years of the 2006–2009 Southeastern U.S. drought. Lake Allatoona reached its highest level since 1990.
Sweetwater Creek
On Monday, September 21, Sweetwater Creek rose to its highest level ever. On September 22, The US Geological Survey measured the greatest flow ever recorded on Sweetwater Creek, at 28,000 cubic feet per second (790 m3/s). The flooding from the creek was met with water from the swollen Chattahoochee River, which blocked Interstate 20 west of Atlanta for two days. Many homes and businesses in the area were completely submerged.
Cherokee County
Interstate 575 was heavily blocked by Noonday Creek, which also blocked several other roads including GA State route 92. The Little River also caused major problems in the same area, blocking the original parallel route of Georgia 5 (which was replaced by I-575 in the 1980s), and Arnold Mill Road, north and east of Woodstock. Commuters trying to get back home to Cherokee County found it took hours due to the numerous road closures and unmarked detours, extending the September 21, 2009 rush hour until after 9:00pm as people sat in gridlocked traffic.
Cobb County
KSU in Cobb county received significant flooding on several parts of campus including the east parking deck. Several buildings and dormitories along Campus Loop Drive were flooded from a nearby creek and lake. Water rushing into the Social Science building reportedly rose up to the bottom of the hand-rail of the first floor stairs. Classes were cancelled at 1:00pm on Monday, September 21 for the remainder of the day and again on September 22 and 23 while damage was assessed and clean-up began Clarkdale Elementary School was flooded to the roof. Students were evacuated early September 21, while waters were ankle-deep. The Cobb school district, wary of rising waters, let middle school students leave before elementary and high schools. Though because of heavy rainfall in Legacy Park subdivision, 3 buses had to return to Awtrey Middle School. Powder Springs Park and parts of Brownsville Road were completely submerged by floodwaters.
City of Atlanta
Inside the city limits of Atlanta, several neighborhoods were underwater, including Peachtree Hills. The Dowtown Connector a section where Interstate 75 and Interstate 85 run concurrent with each other and one of Georgia's busiest expressways, was submerged by the floodwaters. Several cars were swept into the water before police could redirect traffic.
Appalachian Mountains landslides
As a result of the flooding rains, many parts of the southern Appalachian Mountains became saturated. This caused a number of landslides and rockslides, including one in October, 2009 on Interstate 40 in the Great Smoky Mountains of North Carolina. This closed the highway for several months.
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