Is the drought over?
No, says Chuck Bach, manager of River Scheduling at TVA. “The drought appears to be easing, but we’re not out of the woods yet. Conditions have returned to near normal in the western part of the Tennessee Valley, but the rest of the region is still in a serious drought situation.”
According to the latest information issued by the Climate Prediction Center, current conditions vary from abnormally dry in the central Valley to extreme and even exceptional drought in the eastern and southern Valley.
The area above Chattanooga received some welcome rain in January and early February, but rainfall totals from October to mid-February were still only 76 percent of normal. Runoff, the amount of water that reaches the river system when it rains, was even lower—only 39 percent of normal.
Runoff is important because it has a direct impact on reservoir elevations, explains Bach. “When rain falls on dry ground, most of it soaks into the soil. Relatively little runs off into streams and reservoirs, so it takes a significant amount of rainfall to impact reservoir pool levels. To compound the problem, since runoff typically declines in the spring when more water is absorbed by growing vegetation, it will take even more rain in the months ahead to bring reservoir levels up.”
So are tributary reservoir elevations likely to be below normal again this summer?
Not necessarily, says Bach.
“For the past year, we’ve tried to conserve as much water in the tributary system as possible by releasing only the minimum amount of water needed to meet downstream flow requirements. That’s benefited tributary reservoir elevations. Fontana, Douglas, Cherokee, and Hiwassee all were at or above their winter target levels by February and most of the other tributary reservoirs were close to target levels, despite below normal rainfall and runoff.
“The period to watch is March, April, and May. Differences in local rainfall may affect individual reservoirs, but—as long as rainfall during those months is near normal—we should be able to fill most tributary reservoirs to summer target levels on schedule.”
The spring fill typically begins in mid-March. TVA’s goal is to fill most reservoirs to their highest level by June 1.
Keeping reservoir levels at summer target levels will depend on rainfall and runoff throughout the summer.
The ten main-river reservoirs—Kentucky, Pickwick, Wilson, Wheeler, Guntersville, Nickajack, Chickamauga, Watts Bar, Fort Loudoun/Tellico—are all within their normal operating zones. These reservoirs have not been impacted significantly by the drought because TVA is mandated to provide a navigation channel deep enough for vessels with a nine-foot draft.
The National Weather Service is forecasting an equal chance for wetter than normal, drier than normal, or near normal precipitation, so there’s a lot of uncertainty about the weather. Nonetheless, TVA’s tributary reservoir operating strategy is clear, says Bach. “As long as the dry conditions persist, we will continue to operate in a conservation mode. That means maintaining minimum flows and holding any additional water in the tributary system to increase the likelihood of reaching summer target levels.”
Up-to-date information on rainfall, runoff, and reservoir elevations is available here.