The Tennessee Valley got 6 inches more rain than usual during the first half of the year, helping to boost generation from TVA's cheapest energy source last month to nearly double the usual June volume and causing TVA to spill some water through the Chickamauga Dam for the first time during July in five years.
TVA said rainfall so far in 2018 is running 20 percent ahead of normal with 33 inches of rain, on average, falling across the 7-state region in the first six months of the year. Normal rainfall in that period totals 27 inches.
"Runoff trended about 150 percent of normal in June because we've had above normal runoff each month since February," TVA spokesman Travis Brickey said. "The key here is that continued above normal runoff has benefited soil moisture so the rainfall we are seeing is producing more than normal runoff."
That boosted lake levels in TVA reservoirs, keeping tributary storage 2.5 percent above normal for early July, according to TVA records.
It also helped boost hydro electric generation from TVA's 28 power-generating dams by 77 percent above normal in June. The higher level of hydro generation, which supplies about 10 percent of all TVA electricity, is helping to lower TVA's fuel cost portion of power bills this year to 16 percent below the average for July in the past three years.
Higher rainfall and cheaper natural gas is keeping the fuel cost portion of this month's electricity bills at their lowest price since the Tennessee Valley Authority added the monthly fuel cost adjustment five years ago.
But the National Weather Service is forecasting hotter and generally drier weather for the next few days in Chattanooga. although there is a chance of scattered thunder showers each day. The drier weather should limit the amount of runoff and return most TVA lake levels to normal levels within the next couple of weeks.
"We'd expect that (elevated lake level) to quickly change as the summer progresses, as air temperatures climb and if rainfall returns to normal," Brickey said.
TVA helped bring down its swollen lake levels earlier this week by spilling water through most of its mainstream reservoirs, including Chickamauga. This is the first year since 2013 that TVA has spilled water through the Chickamauga Dam in July, although TVA suspended the spilling on Tuesday.
TVA has no current flooding concerns, although Brickey said it is monitoring elevated river levels on the lower Ohio and Mississippi Rivers because releases from Kentucky Dam on the Tennessee River and the Barkley Dam on the Cumberland River can affect levels on the Ohio and Mississippi Rivers.
Contact Dave Flessner at dflessner@timesfreepress.com or at 757-6340.