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Is a hurricane our only hope?

Some say a tropical storm could bring Lake Lanier back to full pool

POSTED: July 29, 2008 5:00 a.m.
TOM REED /The Times

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"The only thing that’s going to help Lake Lanier is a good, strong tropical storm system."

We’ve been hearing meteorologists repeat that mantra all year. But is it really true? With the lake 15 feet below full pool, will even a hurricane be enough to make a difference?

Brett Whitin, hydrologic forecaster for the Southeast River Forecast Center in Atlanta, is skeptical.

"Historically, tropical storms have not had a whole lot of impact," he said. "I don’t think any tropical system coming through is going to be a drought-buster."

Whitin said he and his colleagues recently got curious about how much rain actually makes it into the lake, and they did some research.

"The largest inflow we saw, looking back in history, was in the 1960s," he said. "There was 28,000 cfs (cubic feet per second) coming in over a three-day average. But that wasn’t even from a hurricane. It was just a stationary front that sat over us for a long time."

Occasionally, hurricanes do have a major impact. Whitin said Hurricane Opal, in October 1995, generated an average inflow of 19,000 cfs over a three-day period, pushing up the level of Lake Lanier by more than 3 feet.

By comparison, the average daily inflow at Buford Dam during June 2008 was just 294 cfs.

Whitin said an extra 2 feet of water is generally the most that can be expected from a single storm. For a greater impact, you would need multiple storms occurring over a short period of time.

That happened in August and September of 2004, when hurricanes Frances, Ivan, and Jeanne came in rapid succession.

"Each one generated about 14,600 cfs over a three-day average," said Whitin.

But because the hurricanes struck so close together, the lake did not have time to drop again before the next storm arrived. As a result, Lanier went from 1,069.51 to 1,073.58, a jump of about 4 feet in only one month.

"That’s a good bit of volume," said Whitin. "That’s probably the most active year on record for tropical systems coming into the Lanier basin."

The irony is that much of that water was wasted. With the lake more than 2 feet above full pool, the U.S. Army Corps of Engineers had to release some of it to prevent flooding. And at the time, Lanier didn’t need the water.

"They were close to full pool even before those systems came through," said Whitin.

Now, even if another miraculous confluence of storms occurred, it would scarcely make a dent in Lanier’s deficit.

"With the lake down 15 feet, we’d have to have Noah’s flood come through," Whitin said.

Another problem is that Lanier’s basin is located at the northern edge of Georgia, and tropical storms rarely make it up this far.

"Hurricanes tend to rain themselves out as they come inland," said Kent Frantz, senior hydrologist for the National Weather Service in Peachtree City.

Hurricanes almost never hit Georgia directly. Instead, they tend to pass to the west. But if the storm is large enough, it will have tentacle-like arms that spin in a clockwise direction. Each time one of these arms sweeps through Georgia, it can trigger heavy rains and even tornadoes.

But not all parts of the state will be equally affected. And sometimes, getting rain into Lanier’s watershed is like threading a needle.

"It’s a relatively small basin for such a large lake, and any rain must fall in that basin to have an impact (on Lanier)," said Frantz.

He said when a tropical storm does move through Georgia, the odds of it dumping most of its rain in the Lanier watershed are "in the single digits."

"Tropical Storm Alberto in 1994 sat over North Georgia for three days," Frantz said. "But the heaviest rain fell in the Atlanta area, not in the mountains."

To push all the way up to the Appalachian foothills, a storm has to barrel in like a freight train, fast and heavy.

"The size and speed of the storm can make a difference," said Frantz.

But Whitin said even a powerful hurricane can lose momentum quickly. "A lot of the rain from tropical storms gets dumped below the fall line (that divides north and south Georgia)," he said. "Lanier is not in an ideal spot to receive the benefits."

Whitin said what’s really needed in order to refill Lanier is a combination of two factors: multiple tropical storms this summer, followed by generous rainfall throughout the winter and spring.

"An above-normal winter will really help. That’s prime time for making a big gain in terms of water volume," he said. "But it may take a couple of seasons to get (the lake) back to normal. These big reservoirs just take a while to rebound."



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