An overflowing sewer on Riverside Road, Roswell, Georgia. Photo by Alan Cressler, USGS
The flooding around Atlanta this week is one for the record books. According to the U.S. Geological Survey (USGS), the rivers and streams had magnitudes so great that the odds of it happening were less than 0.2 percent in any given year. In other words, there was less than a 1 in 500 chance that parts of Cobb and Douglas counties were going to be hit with such an event.
“The USGS can reliably say just how bad these floods were. They were epic!” said Brian McCallum, Assistant Director for the USGS Water Science Center in Georgia. “We have all witnessed the devastation caused by these floods, but now we can quantify it.” The data are gathered from the USGS real-time streamgaging network.
The discharge at this site on the Chattahoochee was around 60,400 CFS (cubic feet per second) on Sept. 22, 2009. The river was measured and sampled during the peak discharge that occurred during flooding.
USGS hydrographers using a D-96 weighted sampler. It weighs 132 pounds without the force of water. You can see the heavy steel counterweights on the four-wheel base to keep it from toppling into the water. Hydrographers have to be especially carefully in floods because floating trees can catch the sampler and then everything goes in. Credit: U.S. Geological Survey
Interstate 20 was closed west of Atlanta for around two days because of Sweetwater Creek flowing over it. This U.S. Geological Survey crew is completing a discharge measurement in the west bound lanes of the Interstate. They measured 5,000 cubic feet per second (CFS) crossing the interstate. The crew measuring the discharge at the actual bridge measured around 25,000 CFS. Photo by Alan Cressler, USGS.