Ryan Catlett doesn’t usually take a raft to work.
But that’s exactly what the GPRS Senior Project Manager had to do when tasked with scanning the 98-year-old Ela Dam in North Carolina.
Located in Swain County, along the Oconaluftee River, the Ela Dam – also known as Bryson Dam – is currently being evaluated for removal. It separates the Oconaluftee River from the rest of the Tuckasegee watershed, blocking off the entire Qualla Boundary and parts of the Great Smoky Mountain National Park from their historic drainage pattern.
The Ela Dam is part of the Bryson Hydroelectric Project, and it was originally constructed to provide power to the scattering of houses in rural Swain County. When it came online in 1925, it had the capacity to produce 0.98 megawatts of electricity – a relatively small amount compared to today’s power needs, yet enough to power around 650 homes annually.
On September 3, 2021, Northbrook Energy – which has owned the dam since 2019 – discovered a breech in one of the dam’s gate structures. As Northbrook worked to evaluate the problem, a malfunction in the electronic switches controlling the gates resulted in a release of a slug of sediment from the dam.
These two incidents ¬– combined with the ever-increasing cost of operating the nearly 100-year-old dam – sparked discussions between U.S. Fish and Wildlife Service (USFWS) and N.C. Wildlife Resources Commission (NCWRC) biologists about removing the aging structure and returning water flow along the Oconaluftee to its historic state.
In April 2023, the USFWS approved $4 million to help pay for the demolition of the dam and restoration of the Oconaluftee River. The stakeholders still need to raise at least $6 million from other sources, but once completed, the project will restore 549 miles of watershed, protect the habitats of endangered aquatic species, and help the Eastern Band of Cherokee Indians reconnect to the river which flows through their lands – the Qualla Boundary.
As part of the ongoing effort to create an extensive engineering plan that would guide the removal and site restoration process to ensure minimal impacts to the environment, the stakeholders wanted to know how much rebar is present in the dam’s walls. They intend to allow the eventual demolition contractor to collect the supports and sell the material for recycling, thus allowing the contractor to recoup some of their costs.
Ground penetrating radar is the best tool for this kind of precision concrete scanning.
When operated by a properly trained technician, this non-destructive detection and imaging method can locate both metallic and non-metallic objects buried within concrete or below ground. GPR works by sending a radio signal into a structure and reading the interactions between the wave and any subsurface objects. These interactions are displayed in reading as hyperbolas – smooth curves lying in a plane.
The color of the hyperbolas varies depending on what type of subsurface object is located. Metallic objects – such as rebar - will appear primarily white in a GPR reading, while non-metallic objects appear primarily black.
The shape of the hyperbolas also varies depending on what is located. Post tension cable, for example, is run in bundles and therefore typically has a brighter and wider reaction than rebar.
GPRS Project Managers utilize the Proceq GP8800 GPR Scanner for precision concrete scanning. This handheld, lightweight, and wireless unit was a godsend for Catlett as he maneuvered around the dam in a raft, and then also waded around the structure collecting scans.
The decision to approach the dam in a raft versus wading out to the structure from the shore came from a recommendation from one of the client’s engineers.
“He (the engineer) knew one of the raft guides out there, and so we got a little bit of a discount,” Catlett said. “The raft guy took me out, and I had our gear in a waterproof backpack… And we essentially just rafted to the dam walls.”
Safety is always GPRS’ top priority, and so Catlett made it clear to our client from the start that there were going to be sections of the dam that would be unfeasible to access for scanning.
“The key aspect was that, from the get go, I made it a point of saying ‘Look, I don’t know what this looks like,’” Catlett said. “Nobody had actually laid eyes on this structure yet. If there are areas where we feel it is unsafe, it’s just not going to happen. They were very understanding. They put safety number one, just like we do.”
Despite the challenging conditions, Catlett was able to collect crucial data that will help Northbrook determine how much rebar is present in the dam’s concrete.
This was obviously not a normal day at the office for Catlett – but it was one he won’t soon forget.
“We were out in the mountains, in the middle of nowhere… I mean, you couldn’t have asked for a more beautiful landscape to work in,” he said. “It was extremely memorable from that aspect. It was extremely unique and very memorable.”
No matter the environment our Project Managers are asked to operate in, their standards for concrete scanning remain the same. This is because we utilize the Subsurface Investigation Methodology, or SIM, to ensure accuracy and consistency in our work.
SIM involves 320 hours of field training and 80 hours of classroom training, where technicians like our Project Managers encounter real-world scanning scenarios in a safe and structured environment where they can learn to tackle these challenges. This training ensures that GPRS Project Managers can accurately interpret the readings provided by GPR and other infrastructure visualization technologies.
At GPRS, we put industry-leading technology in the hands of our elite Project Managers to capture hyper-accurate data that helps you Intelligently Visualize The Built World™.
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