Speed of Sound

TVA Surveyors Deploy New Multibeam Sonar

It was a foggy Tennessee morning on the Clinch River.

TVA surveyors Justin Parnicky and Hunter Cardin launched their boat against the backdrop of Kingston Fossil Plant.

“Let’s see what’s out there,” Parnicky said.

Today’s task: Conducting a greenfield survey of the riverbed to see where a pipeline can be placed in support of the Kingston Energy Complex.

These surveys are an important step in the construction process. And now, thanks to a new multibeam sonar, areas that used to take days or even weeks to scan can now be mapped in a few hours.

“Back in the day, you’d stick a rod down in the water and get a physical measurement,” Parnicky said. “Now we’ve got multibeam sonars, which allow us to collect whole swaths of data as we go. It’s interesting to see where this technology is going to take us.”

‘A Pretty Picture’

Looking back at TVA’s history shows where technology could take the region next.

In the 1930s, TVA surveyors mapped the Valley region by air and land, which enabled future decades of construction and resource planning. Today, that legacy continues with modern tools like LiDAR, drones, GPS and sonar.

When Parnicky began his TVA career 17 years ago, underwater data was mostly collected through single beam sonar, which emits a single ping straight down and returns an echo. The system calculates depth using the sound wave’s exact travel time and the known speed of sound in water – roughly 1,500 meters per second.

“This is like the depth finder on your boat,” Parnicky said.

While effective, single beam sonar is limited for inspecting dam structures, profiling reservoir floors or locating debris after storms.

Multibeam sonar solves those gaps by sending a wide sweep of sound across the water column.

Imagine dragging a paintbrush underwater. As the boat moves, the system paints a continuous swath of the bottom, capturing up to five times the water depth in horizontal coverage. In 100 feet of water, up to 500 feet of detailed, real-time data can be collected per pass. The result is a vivid point-cloud depiction that reveals slopes, sediment patterns, structures and debris with clarity and context.

On this excursion, Parnicky and Hardin watched the Clinch River’s topography appear on their monitors as streaks of red and yellow.

“It lets us paint a pretty picture instead of looking at single dots,” Cardin said.

A Better Understanding

Capturing that quality of data requires constant calibration and know-how. Only three people at TVA are trained in this technology as of now.

Until recently, TVA relied on contractors for multibeam surveys. Costs were high and schedules hinged on vendor availability. After Hurricane Helene, TVA needed fast and detailed mapping to assist with debris removal at Douglass Reservoir. The bill approached $200,000 for only a few miles of coverage and TVA leaders saw a better path – investing in capability.

The total cost for fitting the multibeam sonar came just under $300,000, which also included training on how to operate and interpret the data. Given the current pipeline of survey projects, TVA expects to recoup this investment by the end of the calendar year.

Now, instead of waiting on an outside team, TVA surveyors can deploy whenever needed, tailor outputs to TVA’s coordinate systems, and expand how and where the technology is used.

“Not only are we learning to capture the data. We're understanding what goes into capturing it, we're learning how to articulate the data and we're learning what we can do with it,” Parnicky said.

Completing the Picture

That flexibility is already sparking collaboration across the enterprise.

Recent bathymetry projects at Blue Ridge Reservoir and Chatuge Reservoir allowed TVA Dam Safety teams to gather high-resolution mapping of the reservoir bottoms while improving data processing speed and reducing survey time from weeks to days.

The full potential for this technology has yet to be tapped by TVA. Upcoming projects include mapping Normandy Reservoir and potentially Melton Hill Reservoir. They're also supporting archeological expeditions with local university partners. The team envisions a future where every reservoir in the system is fully mapped, an achievement that would enhance stewardship over TVA's waterways.

“It snowballs,” Parnicky said. “You start out with one simple thing and [ask], ‘Now what can we really do with this?’ We really can complete that picture.”

Until that day, TVA Survey continues a nearly century-long legacy of leveraging technology to steward its natural resources and provide benefits to those within the seven-state region.

“TVA Surveying has been here since TVA’s inception,” Parnicky said. “It’s pretty cool to be a part of a legacy like that.”