There’s no question that Tropical Storm Fay did benefit Lake Lanier. By Wednesday afternoon, the U.S. Geological Survey was reporting the lake’s elevation at 1,055.44 feet, about 2 feet higher than it had been on Monday.
That’s still almost 15 feet below the normal full pool of 1,071 feet above sea level. But the storm made up for what had been an extremely dry August.
"Lanier’s already made a pretty nice jump," said Matt Sena, meteorologist with the National Weather Service in Peachtree City. "We’re back above where we were at the end of July."
When you consider the volume of water that Fay dumped on Northeast Georgia, it’s easy to see how the lake was able to rebound so quickly.
On Tuesday, water was flowing into Lanier at a rate of 20,501 cubic feet per second. That’s more than a 2,000 percent increase over the 912 cfs recorded on Sunday, as the storm was moving into the area.
"It’s not unusual to get that amount of inflow after a period of heavy rain," said James Hathorn, hydraulic engineer with the U.S. Army Corps of Engineers, which manages the lake.
Lanier’s collection basin is in the Northeast Georgia mountains, and it doesn’t take long for rain that falls there to make its way down to the lake.
"The response is relatively quick, because the terrain is so steep," Hathorn said. "The peak inflow occurred Tuesday, but for the next three or four days, you’ll continue to see increased inflows compared to what we were seeing last week."
According to National Weather Service records, Gainesville received approximately 6.36 inches of rain between Sunday morning and Wednesday morning, including 3.65 inches on Tuesday.
But the upper basin of the Chattahoochee River, which feeds Lanier, got far more. In Helen, 5.09 inches of rain fell Tuesday, causing the river to briefly overflow its banks.
And during the 72-hour period, as much as 11 inches fell on parts of Habersham County, according to radar-derived estimates.
"The mountains had more rain because the wind was being pushed up ridge slopes," Sena said.
Though most of that rainfall quickly began moving downstream toward Lanier, it also saturated the parched ground.
"(Fay) did benefit the topsoil," said state climatologist David Stooksbury. "Definitely the drought is not as bad this week as it was last week. (But) if it doesn’t rain for a week now, we will see streams return to very low flows, though maybe not quite as low as they were before the event."
Though everyone is weary of rain at this point, Hathorn said now is the best opportunity to capitalize on the lake’s improvement.
"When the ground is saturated like it is, any rain becomes runoff," he said. "So now is the most beneficial time to have an additional rain event."
Though there is a 20 to 30 percent chance of thunderstorms over the Labor Day weekend, Sena said there won’t be a soaker like the one we’ve just experienced.
"We cannot rule out pop-up summertime storms, but nothing on the scale of what we had with Fay," he said.
Another tropical storm, Gustav, is lurking off the coast of Cuba, but Sena said it’s much too early to predict where it will go. "We won’t know until the beginning of next week, at the earliest," he said.
Forecasters also failed to predict the impact of Fay. Though not a hurricane, Fay was a big rainmaker because it stalled out, moving very slowly up through Florida, South Georgia and finally North Georgia.
Because of the storm’s stealthy behavior, corps officials were way off target when they made their latest four-week projection for Lake Lanier.
On Tuesday, the corps released its weekly outlook, estimating that Lanier would be at 1,053.7 feet by Sept. 5 and 1,052.6 by Sept. 26.
"More rain fell into the basin than we predicted," Hathorn said, adding that next week’s projection would be revised to account for the impact of Fay.
He said most of the rise in Lanier was caused by increased inflow, not by the corps holding back on its releases from Buford Dam.
But Hathorn said the corps did cut the amount released by 50 percent on Monday and Tuesday. The agency is required to meet a minimum flow of 750 cfs at Peachtree Creek in Atlanta, in order to dilute sewage from metro treatment plants.
But because creeks in the Atlanta area were already high, no additional water was needed from Lanier.
Hathorn said the corps will decide on a day-to-day basis whether to increase releases from the dam. "We’ll continue to look at the situation downstream," he said.