Flood — Cobb, Georgia

2009-09-21 · near Acworth, Cobb, Georgia

Event narrative

Although flash flooding began to subside, extensive flooding was reported across the county and confirmed from several USGS stream gages. Flooding expanded on areas earlier dexperiencing flash flooding. Record flooding was observed along Sweetwater Creek near Powder Springs, Powder Springs Creek, Noses Creek, and numerous other small creeks and tributaries. At least 100 roads across the county were closed, including portions of Interstate 20 and Interstate 285 near Six Flags. Extensive rescue operations were conducted in many areas of the county as motorists found their vehicle submerged in flood waters. At least a dozen people were evacuated in Powder Springs because of rising water from Sweetwater Creek near their homes. Other neighborhoods in south Cobb county were also flooded. Damage to home and businesses throughout much of the county was tremendous. During this time period alone, it was estimated that roads and property in the county sustained damage nearing $6 million.

Wider weather episode

A historical, record, and catastrophic flood event unfolded during this period, mostly in the west central Georgia area, including the western and northwestern suburbs of Atlanta. Major flooding was noted in many other areas of north and central Georgia, including the eastern suburbs of Atlanta, northwest Georgia, and parts of central Georgia. The culprit was a very stagnant upper atmospheric pattern featuring a weak upper low that developed in early September across south Texas and slowly migrated east-northeast through September 22nd, until a more significant upper trough dropping south into the southern plains finally moved the pesky upper low northeast of Georgia. In addition, an unusually deep tropical flow was noted throughout this period. Precipitable water values exceeded 2.0 inches across the area during much of this period, resulting in extremely efficient rain producing cells. Persistent heavy rain showers and thunderstorms began to plague the area on the 16th, and persisted daily through the 21st across parts of north and central Georgia.

However, the catastrophic flooding unfolded when a sea breeze moving northwest merged with existing outflow boundaries and higher terrain across the western suburbs of Atlanta to result in persistent heavy thunderstorms for a period of at least 12 hours that trained across the same counties west of Atlanta, generally affecting Carroll, Douglas, Paulding and Cobb counties. As the activity progressed across the state, significant flooding unfolded further east, including Fulton county, and the city of Atlanta, DeKalb, and Gwinnett counties. Incredible rainfall amounts of 15 to over 20 inches, were observed from northeast Carroll, through much of Douglas, into eastern Paulding and southern Cobb counties. Rainfall amounts of 10 to 15 inches were noted across parts of Fulton, Dekalb, and Gwinnett. Rainfall amounts of 8 to 12 inches were noted in other more spotty areas of northwest, north central, and central Georgia during this period.

The excessive rainfall on top of saturated ground resulted in some of the worst flooding ever reported in the Atlanta and north Georgia area. Eleven deaths were recorded during the event, mostly vehicle related deaths at night from washed out bridges and roads as a result of swollen creeks. Property damages are estimated to be at least $0.5 Billion, with hundreds of homes and businesses destroyed by flood waters. Bridges on several state and local highways were washed out and some will take months to even a year to replace. Eighteen counties (Bartow, Carroll, Chattooga, Cherokee, Cobb, Coweta, DeKalb, Douglas, Fulton, Gwinnett, Heard, Newton, Paulding, Rockdale, Stephens, and Walker) received a presidential disaster declaration as a result of the historic floods. Twenty-one counties were declared eligible for public assistance, including several central Georgia counties that were affected by flash flooding earlier in the period.

Some of the worst flooding was observed along Sweetwater Creek near the Cobb, Fulton, Douglas county line. Hundreds of homes were flooded and destroyed as the waters of Sweetwater Creek rose more than 20 feet above flood level.

Many main stem and secondary creeks, streams, and rivers across north and central Georgia, particularly in northwest and west central Georgia, reached record flood levels. Many of these same creeks, streams, and rivers remained in flood for several days. In some cases, all time record flood levels were recorded. The following is a list of new record flood levels set on several creeks, streams, and rivers in north and west Georgia. Noonday Creek near Woodstock rose to 19.6 feet on the 21st at 530 pm EDT. The previous record was 16.30 feet set on July 11, 2005. Nickajack Creek at Mableton reached 19.30 feet on the 22nd at 215 am EDT. The previous record was 16.60 feet set on July 11, 2005. The North Fork of Peachtree Creek at Atlanta rose to 18.07 feet on the 21st at 715 pm EDT. The previous record was 17.70 feet set on September 16, 2004. Utoy Creek near Atlanta rose to 27.04 feet on the 22nd at 1000 am EDT. The previous record was 16.86 feet set on May 6, 2003. The Chattahoochee River at Whitesburg rose to 29.61 feet on the 21st at 745 pm EDT. The previous record was 29.11 feet on December 11, 1919. Suwanee Creek at Suwanee rose to 14.30 feet on the 21st at 645 pm EDT. The previous record was 12.04 feet set on October 5, 1996. The Yellow River at Lithonia rose to 25.50 feet on the 22nd at 515 am EDT. The previous record was 17.53 feet set on May 7, 2003. The Yellow River near Conyers below Milstead rose to 22.54 feet on the 22nd at 500 pm EDT. The previous record was 16.36 feet set on July 8, 2005. The Chattahoochee River at Franklin rose to 29.98 feet on the 22nd at 500 pm EDT. The previous record was 28.40 feet set on December 15, 1919. The Sweetwater Creek at Austell rose to 30.17 feet on the 22nd at 1000 pm EDT. The previous record was 21.81 feet on July 12, 2005.

The following rivers reached flood levels that were within the top five all time levels at these locations. Peachtree Creek in Atlanta rose to 23.89 feet on the 21st at 915 pm EDT. The all time record is 25.80 feet recorded on December 20th, 1919. Nancy Creek in Atlanta reached 14.69 feet on the 21st at 930 pm EDT. The all time record is 15.50 feet on December 1, 1973. The Chattahoochee River at Vinings reached 28.10 feet on the 22nd at 1200 am EDT. The all time record is 29.0 feet set on December 10, 1919. The South Fork of the Peachtree Creek reached 15.21 feet on the 22nd at 1200 am EDT. The all time record is 29.0 feet set on December 10, 1976. The Chattahoochee River at Campbellton reached 30.55 feet on the 22nd at 300 pm EDT. The all time record is 31.60 feet set on December 10, 1919.

View location on OpenStreetMap → (34.0800, -84.7300)

Source: NOAA Storm Events Database, event_id 200741. Narrative written by the NWS forecast office that issued the report.