Sept. Atlanta flooding: 1 in 10,000 event

ATLANTA, Nov. 5 (UPI) -- The U.S. Geological Survey says the September flooding that inundated the Atlanta area was so extreme, scientists say the data are stunning.

"At some sites, the annual chance of a flood of this magnitude was so significantly less than 1 in 500 that, given the relatively short length of stream-gauging records, the U.S. Geological Survey cannot accurately characterize the probability due to its extreme rarity," said Robert Holmes, USGS National Flood Program Coordinator.

Brad McCallum, assistant director for the USGS Georgia Water Science Center in Atlanta, said the flood waters overtopped 20 stream gauges -- one by 12 feet. "This flood was off the charts," he said, calling the event "near the top of the list of the worst floods in the United States during the past 100 years."

The National Weather Service said some locations recorded up to 20 inches of rain from 8 p.m. Sept. 20 to 8 p.m. the following day. "Applying rainfall frequency calculations, we have determined that the chance of 10 inches or more occurring at any given point are less than one hundredth of one percent," said Kent Frantz, NWS hydrologist. "This means that the chance of an event like this occurring is 1 in 10,000."