Drip, Drop

Precise Instruments Help Guide River Forecast Center Operations

At his home, TVA senior instrument mechanic Ralph Nunley has a commercial-grade weather station that measures all types of data: wind speed, barometric pressure, rainfall and more.

“My rain gauge at home recorded 3.86 inches of rain in the last 30 days,” he said, observing recent drought conditions in the region. “My love of weather came from this job. It lit a fire.”

On a recent visit to Nickajack Dam, Nunley approached a small contraption in the corner of the fence along the dam – a metal funnel perched on a post. It's one of 60 rain gauges that he oversees across his territory.

Up close, the gauge looks simple. But inside, there are intricate measurements happening.

Rainfall is pulled into a narrow channel, funneled down to a tipping bucket inside – a little seesaw that fills, clicks and empties with every 0.01 inches of water. Each tip sends a pulse to a sensor. Once every hour, the whole thing wakes up and beams that data to a satellite, carrying the last 60 minutes of weather data to the River Forecast Center (RFC).

“They plug all this information into the model and determine how much water they need to release across the region,” Nunley said.

These tiny tipping bucket mechanisms are responsible for determining how TVA manages our waterways – surprisingly delicate calculations for such a mammoth undertaking.

Nunley performs calibrations twice a year on all his gauges. Using a standardized bottle that should trigger 100 tips – that’s 1 inch of rain – he ensures that the gauge aggregates accurate readings.

Water flow, dam releases and recreation safety depend on it, further emphasizing TVA’s vital role in public safety.

In addition to digital calibration work, there is also a notebook that rests inside the cabinet – its wrinkled pages a nod to analog documentation from days gone by. These handwritten records hold nearly a decade’s worth of data, and these backup calibration logs allow Nunley to quickly cross-reference data and see how measurements and equipment function have ebbed and flowed over time – a hydrologic history.

“I learn something new every day I work here,” he said. “And this little book has really held up. It’s fun to look back and see my calibrations over the years.”

One of his colleagues, engineering technician Brandon Boyd, blends fieldwork and instrumentation expertise. Another aspect of hydrologic monitoring that goes hand in hand with the rain gauges is measuring water depth.

The way Boyd describes it, measuring headwater and tailwater levels feels a little like taking the pulse of a living river.

Under the hatch, the gauges look old-school – weights, pulleys and a long, narrow tape that reacts to the slightest rise or fall in the water. The system tracks the elevation of the water above the dam (the headwater) and below it (the tailwater).

All of this data flows into TVA’s River Forecast Center, a 24/7 operations hub where hydrologists and engineers use raw measurements to make real time operational decisions to manage the river system.

They combine rainfall, streamflow and reservoir data with weather models to determine how to maximize the benefits of the river system and forecast river flows and water levels hours and days ahead. Those forecasts guide operational decisions across the entire system – from generation and flood control to navigation, recreation releases and water quality.

“Our instrumentation mechanics and engineering technicians are critical to keeping the RFC informed so we can make the best operational decisions,” said Darrell Guinn, River Forecast Center Senior Manager. “Knowing how much and where it rains or what the water levels are across the Valley region helps the RFC make decisions – whether its's reducing flood damages or maximizing hydroelectric power generation to take advantage of Mother Nature’s fuel.”

Although Boyd is on the front lines of a lot of these granular engineering projects, he also likes looking at the bigger picture.

“A lot of people think TVA is just a power company,” he said. “They don’t realize all the stories about flood control and all the outreach in communities. Our scope is so much larger than people think.

“To help people understand, I tell them my piece of the puzzle and explain how it all fits.”

As the noontime sun began to chase away the cool morning, Boyd shed his outer layer – a worn chore coat with TVA embroidered on the chest.

“This is actually my mom’s old shirt,” he said. “Both my parents were operators at Raccoon Mountain. I grew up around this and now I’m here, too."