• 15.2 inches: Rainfall so far this year in the Tennessee Valley above Chattanooga
• 19.3 inches: Normal rainfall in a typical year to this point in the Tennessee Valley
• 79: Percent of normal rainfall and runoff into reservoirs so far this year
• 84: Percent of normal hydroelectric generation in May because of lower rainfall
• 65: Inches of rain during all of 2013, the wettest year in TVA history
Source: Tennessee Valley Authority
For the Tennessee Valley Authority, every inch of rain is worth more than $10 million.
With rainfall so far this year more than 4 inches below normal in the Tennessee Valley, TVA and its ratepayers will soon pay the price for all those sunny days this spring.
The lack of rain in March and April - the driest spring since the year 2000 - also means three of TVA's 10 East Tennessee reservoirs will have lake levels this spring anywhere from 9 feet to 15 feet below normal summer levels.
"We're holding on to every drop of rain that we can hold on to and releasing only the minimum amount to maintain our minimum flow levels in the river, but we're just not getting enough rain," Tom Barnett, senior manager of TVA's river forecast center in Knoxville, said Monday. "If we get some rain, it would certainly help, but I'm not sure we're going to get to normal summer pool levels in some of our reservoirs."
The drier spring this year comes after the wettest year in TVA history during 2013 when more than 65 inches of precipitation fell across TVA's 7-state region - more than 13 inches above normal for the year.
TVA generated a record amount of more than 19 gigawatthours of electricity from its 29 power-generating dams last year. Hydro power is TVA's cheapest source of energy and through most of the utility's history has helped keep TVA residential electricity rates among the lowest in the nation with more than $500 million a year in virtually free power for TVA.
While TVA often operated its network of 49 dams last year for flood control, such managers are trying to use this year's more limited rain to sustain TVA's other river interests in navigation, water quality, power plant cooling and recreation, in addition to flood control.
TVA was established in 1933 to manage the Tennessee River and its tributaries for power, flood control, economic development and recreation.
"Everything we do at TVA pretty well starts with a drop of rain," TVA spokesman Jim Hopson said.
But with limited rain this spring, TVA's hydro generation is running 16 percent below normal so far in May. That could continue to push up TVA's monthly fuel-cost adjustment on power bills in coming months.
Barnett calculates that every inch of rain above Chattanooga in the Tennessee Valley is worth more than $10 million in extra hydro generation, and likely worth even more in the value of sustaining other power generating plants with water cooling and in supporting river navigation and recreation in the Valley.
TVA initially derived all of its power from its hydroelectric dams, which today comprise only about 10 percent of TVA's power. But TVA coal and nuclear power plants still use water from the Tennessee River or its tributaries for cooling. Less rainfall requires the utility to convert to more expensive water cooling from cooling towers during dry periods.
"We're already operating our cooling towers which means we will have less output for our public from our economical nuclear units," TVA President Bill Johnson told the agency's board last week. "We are hoping for rain in the tributaries in the east and if there is anything anyone can do about that, it would be helpful,."
Barnett said he has washed his car, done a rain dance and said a prayer for rain, but weather forecasters are still predicting only an inch to 1.5 inches of rain in the eastern half of the Tennessee Valley during the next 10 days. To replenish all of its reservoirs would take about 8 inches of rain during the balance of May, or twice the normal level, Barnett said.
"It's looking like it will be a warmer summer than normal, and that often means it could also be drier than normal," he said.
Barnett said among the 10 major tributaries above Chattanooga, "seven are filling pretty well."
But in the three reservoirs in the northern half of the Valley - Norris, South Holston and Cherokee - "we've only gotten about 50 percent of the normal rain and they are likely to be well below normal summer pool levels," Barnett said.
"For boaters who are not used to the lower levels, we are asking them to be extra careful as they boat this summer," he said.
Contact Dave Flessner at email@example.com or at 757-6340.