Yesterday, I mentioned that even though none of the daily rain events amounted to more than 10-year storm event, the cumulative effect of a week’s worth of storms manifested itself as a 100-year storm on Monday and into Tuesday.
Turns out that the US Geological Survey is actually saying that in many cases, this was a 500-year event.
“It is epic!” said Brian McCallum, assistant director for the USGS Water Science Center in Georgia. “The USGS can reliably say just how bad these floods were.”
They are calling this a 500-year flood because of the likeliness of it occurring is so rare, said McCallum. “We could have another flood next year, or floods back-to-back and still be considered 500-year floods because of the probability.”
Here is where the big problem for flooding in homes of people who didn’t have flood insurance comes in. The National Flood Insurance Program offers insurance to those who have property in the 100-year floodplain, not the 500-year floodplain. The 500-year floodplain is actually shown on many FEMA FIRM (Flood Insurance Rate Map) panels. If you’re curious to see where you property sits relative to a floodzone, you can search for flood maps at this FEMA website.
The Army Corps of Engineers, which has been a frequent target of criticism in Georgia, once again is on the defensive with regards to water releases from Lake Lanier during the floods. The Corps had this to say:
“The corps curtailed its operations on Sept. 19, and only minimal releases of approximately 670 cubic feet per second released through the small house unit have continued,” Coghlan said.
Those releases, about 300,000 gallons per minute, equated to less than an inch at a gauge 30 miles south of the dam in Vinings, according to the corps.
“Releasing from the small unit did not contribute to the localized flooding in the metro Atlanta area,” Coghlan said.
Coghlan said the flow out of large dams is rarely halted completely due to adverse impacts on river environments. The small unit generates power for the dam and project offices and “assisted in maintaining viable conditions for essential habitat below the dam,” Coghlan said.
As is usually the case with the Corps, their statements usually lead to more questions. While I doubt that releases of 670 cubic feet per second did much to exacerbate downstream flooding, the Corps apparently does have the ability to cut off all flow from Buford Dam according to Coghlan. Under what circumstances would the Corps actually do this? Coghlan correctly points out that cutting off all flow from Buford Dam would have some fairly bad consequences for the immediate area below the dam – the river would essentially be dry immediately below the dam. But what is the “essential habitat” and is 670 cfs the minimum amount of maintain “viable conditions”? Coghlan maintains that releasing did not contribute to the localized flooding downstream, but hardly seems like an accurate statement. If it’s a matter of adding no water versus adding water, then releasing certainly would contribute to the flooding. It may have been immaterial, but it certainly did contribute. By its own admission, the release added an inch to a gage 30 miles away, so on one side they say the didn’t contribute, but then acknowledge that their gage data shows they did. Of course, the Corps has earned a reputation for gage reading too.
Unfortunately for the Corps, they’re stuck in a pretty difficult position given the current legal battles going on between Georgia, Alabama and Florida. The fact they’ve become a common target doesn’t mean they’re at fault every time the weather gets wacky in Atlanta – be it drought or flooding. However, their communication of what they’re doing, how they’re doing it and why they’re doing it leaves them open to criticism. They would be wise to be more open about their operations and less defensive about their actions.
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