Water, Water Everywhere?
It’s time for the spring fill—which means that TVA’s River Forecast Center is turning it’s eyes to the 2017 recreation season and holding on to water in the reservoir system.
MARCH 13, 2017—It’s a gray rainy day in March—the kind of day that might find you sagging at your desk or lagging in bed. But at TVA’s River Forecasting Center, the mood is buoyant. This is a welcome rain, much needed for this year’s annual spring fill of the reservoir system.
Despite what feels like endless drizzle, conditions in the Tennessee Valley are dry. “We’ve just come off the heels of a very dry 2016, a year that saw much of Valley in moderate, severe or even exceptional drought for at least ¾ of the year,” says James Everett, manager of Operations Support for the River Forecasting Center. “And now we’re in 2017, and we’re already falling behind in precipitation—we’re behind 1½ inches on rainfall for the year, and 3 inches for runoff.”
In fact, according to the U.S. Drought Monitor, the entire Valley is currently categorized as abnormally dry, with pockets falling into moderate or severe drought.
And that drought has given rise to an even bigger problem, reservoir-wise: lack of runoff. “Already we’re behind 3.4 inches for the year, or 54 percent of normal,” explains Tom Barnett, senior manager of the River Forecast center. “Runoff is lagging even further behind the rain because the soil is so thirsty after last year’s drought. And now we’re looking at an early spring—as plants begin to bud and leaf out, they’ll be competing for that runoff, too.”
The Big Fill
These are challenging conditions, as TVA relies on Mother Nature for the rain and run-off necessary to fill the reservoirs on the Tennessee River system in the spring. “We just haven’t had those big 4- or 5-inch rain events we usually see in the wintertime,” Everett explains. “In order to get to a normal spring fill, we’ll need to have 1 inch to 1½ every week between now and the beginning of June.”
And that’s a potential problem—especially for the big tributary reservoirs of East Tennessee. “The big tributary lakes have to come up dozens of feet each year,” Everett says. “For instance, Cherokee has to come up 24 feet; Fontana needs to come up 48 feet to be at full pool.
The reservoirs will fill when rainfall and runoff accumulate and TVA scales back operations to minimum flow levels in order to effectively hold onto every possible drop, which means reducing hydropower production and only providing minimum flows for water quality. That process usually revs up in mid-March. This year, a few of the big tributary lakes—Cherokee, Douglas and Norris—the River Forecasting Center started in February, with a healthy dose of cautious optimism.
“We’ve been watching the weather very closely, and when conditions look favorable to hold onto water, we are doing that,” Everett says. “But we have a mission of flood control, too—and we take that very seriously.”
Low and Slow
As for the reservoirs on the main river stem—such as Ft. Loudon, Guntersville and Kentucky—low and slow is the name of the game. “Those reservoirs only have to come up maybe 4 or 5 feet,” Everett explains, “and when we take them up we want to make sure we can keep them up so that we’re supporting aquatic life. For example, if we raise water levels and fish spawn in shallow areas, there’s a danger of stranding eggs if we lower the levels again. We don’t want to do that.”
Moreover, flow on the river system is critical for many other reasons—some many residents of the Valley simply don’t think about. “Recreation is the most visible part of what we do, but we’re managing the river system for multiple benefits,” Barnett explains. “We’re making sure it has good dissolved oxygen levels to support aquatic life, that there is flow sufficient to assimilate waste so water quality is high, that municipal and industrial water intakes are under water, and that we have the cool water we need to support operations at our coal and nuclear plants.”
According to TVA’s River Operating Guide, the fill starts in earnest on March 15. “That’s when we really get aggressive about holding onto water across the system,” Everett says. “We’ll continue to fill through June 1. And those three months—March, April and May—will tell us a lot about how we’ll be managing the river throughout the summer and fall.”
At the same time, Barnett notes, anything can happen: “Right now, the long-range forecast show equal chances of being normal, above normal or below normal. We’re in a good place right now, and just have to hope for normal to slightly above normal rainfall.”
Come on April showers!