Thurmond Lake has risen 27 inches since its 2007 low on Christmas Day, but without a rainfall boost from tropical weather in the Augusta area later this year, there still could be problems during the summer and fall.

At its low point, the 70,000-acre lake had fallen to 316.18 feet above sea level, or almost 14 feet below full pool. As of Thursday, it had risen more than 2.3 feet, to 318.49.

"This is typically our wet season and we anticipate it will continue to come up for the next four weeks," said Army Corps of Engineers hydrologist Stan Simpson.

Once the wet period ends, however, it becomes more difficult for the lake to refill.

"There is usually lots of rain in February and March and into April, but after that it starts to dry off," he said, noting that trees and plants will consume more of the available moisture after spring.

Although recent rains caused some streams to overflow, such flooding has little impact on large reservoirs, he said.

"When you think about those streams and compare them to the lake, the lake is a huge surface," he said. "For it to rise you need a lot of rain on that surface. When you look at a stream, it doesn't take a lot of rain for the stream to look like a lot of water."

A line of thunderstorms on Tuesday dumped an average of 1.23 inches of rainfall in the Savannah River basin, which includes lakes Thurmond, Russell and Hartwell, which collectively include 156,000 acres of water.

Earlier rains had rehydrated soils in many areas, making it possible for more rain to run off into reservoirs.

"Three days prior to the big rain we had a half-inch, which primed it for a good runoff," he said. "So that was the kind of rain event we want."

During 2007, a three-inch rainfall in the region pushed the lake up four feet in four days -- from 325.75 on March 1 to 329.8 on March 5. Although this year's outlook is improving, Mr. Simpson said much more rainfall is needed to replenish the lakes.

"We had a slight excess of rain in December, with January about two-thirds of normal," he said. "February was just shy of normal so what we will need, as we get out of our rainy period, is twice the normal rainfall, unless we get a tropical event."