Hydro Review: Safer, Swifter Dam Inspections

Sonar technology lets Tennessee Valley Authority’s dam safety inspectors see on and around dams to identify potential problems without ever having to leave the boat.

By Scott Fiedler

Time was, dam safety inspections meant climbing, crawling and diving. Today — thanks to some nifty new technology — it also includes boating and monitoring.

Underwater acoustics, or sonar, can produce 2D and 3D images of dams using a boat-mounted device, and these images can then be used to identify potential maintenance issues in real time. The sonar system has the capability to rotate 360 degrees and tilt plus or minus 45 degrees to provide a wide range of perspectives.

The Tennessee Valley Authority started using this technology on remotely operated vehicles (ROV) in 2010 to aid in navigation and inspection. Since then, TVA has been able to use the technology to assess spillway apron condition, identify damaged or missing concrete components, and quantify sediment and debris loads with both ROV and boat-mounted sonar systems.

Keeping everyone safe

With safety of employees and the public as its top priority, TVA’s dam safety team and independent structural experts work to ensure that TVA’s 49 river dams — including many earthen structures — conform to federal design, operation, maintenance and repair guidelines.

TVA inspects its hydro facilities monthly, as well as on 15-month and five-year intervals, to look for signs of erosion or any other issues that may cause concern, such as seepage and concrete deficiencies.

These inspections are part of a robust, comprehensive dam safety program that also includes:

  • Continuous electronic monitoring for vibrations;
  • Rigorous structural and geological assessments;
  • Surveillance not only of the surface of hydro structures, but also the geology under and around the dams.

Some of TVA’s dams are more than 100 years old. Sonar allows TVA to perform health checks tailored to each dam and monitor changes over time.

Saving money, saving time

The sonar system TVA uses can be deployed quickly from an ROV or a tripod or mounted to the side of a boat, enabling inspections that would have taken divers a week to complete to be conducted in a single day. With the 3D sonar head, the setup also allows for the integration of GPS technology for real-time scanning and hydrographic surveying.

The point clouds produced using the 3D sonar allow TVA engineers and inspectors to assess the condition of dams, view underwater contour features and conduct detailed inspections.

This photo shows a combination of above-water LiDAR scans from TVA surveying equipment and underwater sonar scans from TVA dam safety inspections of Wilson Dam.

“This system allows us to see the dams more effectively and efficiently, and improves our ability to conduct dam safety inspections,” says Benjamin Phillips, TVA manager of dam safety inspections. “These inspections help us identify any potential problems before they can become serious issues.”

The sonar system also saves money. Inspections can be conducted while turbines are running and power is being generated, whereas traditional methods with divers require generation to be stopped, resulting in lost power costs. “The sonar is a great addition to our program and provides real benefits to our dam safety inspections,” Phillips said. “We are able to look at the entire facility, whereas with divers, you’re really only able to look at what you can reach.”

An example that shows the benefits of using sonar is scour inspections on main river spillway aprons. Previously, a dive crew would perform the inspection, which would tie up a five-man crew for about eight days. (Five people x eight days x eight hours per day per person = 320 hours.) With sonar scanning, TVA can use three people for two days at eight hours per day, or 48 hours total. This results in a net savings of 272 man-hours.

Protecting human life and property through flood control is part of TVA’s core mission. According to Phillips, TVA has invested more than $360 million on dam improvement since 2010. As a result, TVA’s dams and river management has helped avert more than $7.9 billion in flood damage over the years.

Sonar inspection also improves public safety because TVA is now able to review areas more frequently than before.

Scott Fiedler is in media and public relations with the Tennessee Valley Authority.

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