0715lakeaudState climatologist David Stooksbury explains why recent rains have not helped Lake Lanier.
Much of Northeast Georgia was pounded repeatedly by heavy rains last week, with some parts of North Hall and White counties receiving as much as 3 inches, according to radar-derived estimates.
Since those areas are within Lake Lanier’s watershed, all that rain must have been good for the lake, right?
Not exactly. On the Fourth of July, Lanier stood at 1,056 feet above sea level, which is 15 feet below its normal full pool. On July 13, it was at 1,055.95.
True, the lake did rebound slightly after dropping to 1,055.79 on July 8. But its level has fluctuated by only a few inches this month.
The recent rains have been like a breath of fresh air to Northeast Georgia, greening up lawns and bringing wilting plants back to life. But why didn’t the rain help Lanier?
"It’s really indicative of how dry it is. Much of the water is being held by the soil," said state climatologist David Stooksbury. "July is one of our wetter months, but moisture loss due to evaporation and plant use is so great during July that soils still have a tendency to dry out."
A telltale sign, Stooksbury said, is how quickly streams rise and then fall after a rain.
"You’ll see an initial stream surge due to runoff, but then the next day it looks like it never rained," he said.
Mike Leary, meteorologist with the National Weather Service in Peachtree City, said the strong storms last week were caused by "a cold front that got hung up in the area and just stayed around instead of moving on."
But though the rain was heavy in some locations, the effect was scattershot.
"Lanier has a very small watershed, and most of the storms are not quite hitting it," Leary said.
Patrick Robbins, spokesman for the U.S. Army Corps of Engineers’ Mobile district, which manages Lanier, said the lake always has suffered because its tiny catchment basin is inadequate for such a large body of water.
"It’s a 38,000-acre lake, so it takes a great deal of rain to fill it up. It would have to go on for days and days and days," he said. "And the rain has to fall in certain areas to be beneficial to the lake."
James Hathorn Jr., hydraulic engineer for the corps in Mobile, said it’s not accurate to say the rain didn’t help Lanier. He pointed out that at least the water level is holding steady instead of dropping further.
"The decline has stopped," he said. "There were two rain events that allowed us to ‘flatline,’ but we need to have continued events like this."
Hathorn said last week’s rains brought the lake closer to an optimal situation.
"Now that the ground is saturated, any additional rainfall would benefit the lake," he said.
Unfortunately, there’s no rain in the Gainesville forecast until Friday, and even then it’s only a 20 percent chance. Stooksbury said we shouldn’t expect a repeat of last week’s abundant storms.
"A cold front this far south in July is kind of unusual, so I wouldn’t count on it happening again," he said.
The bright spot is that southwest Georgia also has received a decent amount of rain. The two lakes below Lanier in the Apalachicola-Chattahoochee-Flint river system, West Point and Walter F. George, are close to full.
If they weren’t, the corps would have to release more water from Lanier in order to protect endangered aquatic species near the Florida border.
"There’s enough storage to meet minimum flow requirements at those reservoirs," Hathorn said.
Right now, the corps is only releasing enough water from Buford Dam to meet the minimum flow requirement of 750 cubic feet per second at Peachtree Creek in Atlanta. That amount is necessary in order to dilute Atlanta’s sewage discharge into the Chattahoochee River.
Hathorn said as far as the corps is concerned, the critical rain is not what falls into Lanier’s watershed, but what falls below Buford Dam.
"Any rain that falls between the dam and Peachtree Creek allows us to release less," he said.
In fact, after a heavy rain Wednesday, the corps cut its Buford Dam release from 1,056 cubic feet per second down to 618. That was a precaution, Hathorn said, to prevent flooding in Atlanta.
"You can go from a drought operation to a flood-control operation very quickly," he said.