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TVA: October rain runoff lowest in 140 years

Posted on Thursday, November 17, 2016 at 12:32 pm

October’s rain runoff level in the Tennessee Valley was the lowest in 140 years of record keeping, according to the Tennessee Valley Authority, which is closely monitoring effects of the current drought.

“It’s very dry across the entire Tennessee Valley,” Jim Hopson, TVA public relations manager, said Tuesday.

“In fact, during October, we only averaged about 0.9 inches of rain runoff, which is the portion of precipitation that actually makes it into streams and rivers, and that’s the lowest runoff level for October we’ve seen in 140 years of record keeping.

“Since Normandy and Tims Ford dams are tributary reservoirs, they depend on runoff for fill, so an extended drought could affect our ability to refill them over the winter and into next spring.”

Hopson said.

“It’s all up to Mother Nature at this point,” he said, “but we are working to manage the entire river system to help ensure good water quality even during this dry spell.”

On Nov. 1, the water level on Normandy Lake on the Duck River in Coffee County was .25 feet below summer pool of 865 feet below sea level. (The top of the dam is 880 feet.) Winter pool, for which drawdown has not been implemented, is 852 feet.

Also on Nov. 1, the stream discharge from the dam was at 159 cubic feet per second. Duck River is the main water source for downstream cities that include Shelbyville and Columbia.

Tims Ford Lake, the major portion of which is in Franklin County, was at 2.70 feet below full pool of 888 feet.

Tims, which produces electric power on the Elk River, was discharging 80 cubic feet per second downstream on Nov. 1. The discharge increases when the dam is producing electricity.

Drones reduce cost

In other information provided by TVA, drones are helping to reduce costs and human risks involved in inspecting TVA dams and equipment.

Normandy and Tims dams will be included in the drone inspection program in the future, Hopson said.

“Keeping its dams performing well and the communities near them safe is a top priority for TVA,” Hopson added. “That’s why TVA monitors its dams routinely and continuously updates its dam safety program to meet current industry standards. The drones are a new part of our ‘toolkit’ for dam safety.”

He said he expects the drones to be used at Normandy and Tims Ford during the next full inspections at those locations.

“We do dam safety inspections all of the time, Hopson said, “but the major dam safety checks are only done occasionally. Think of the routine inspections as being similar to your normal doctor’s office visit and the dam safety checks as being like major diagnostic tests, like colonoscopies, which are only done every 5 to 10 years.”

Scott Kramer, manager of TVA Dam Safety Inspections, said the unmanned aerial vehicles (UAVs) “are offering TVA a safe, cost-effective alternative to human rope-access inspections.”

According to Kramer, TVA is regularly inspecting a number of exterior features such as spillway gates that are crucial to the safety of the dams.

Dam safety officials regularly contract with engineering firms to perform rope-access inspections to inspect the entire dam face for cracks, joint offsets, concrete damage, gate misalignment and overall condition, said Kramer.

“While appropriate safety measures are always employed, there is inherent risk in performing rope-access inspections of these features at our dams,” he said.

“The drone is video equipped and will allow us to inspect these dams more safely and expeditiously. We plan to operate the drone from locations on or near each dam on federal property in TVA’s custody and control.”

Benefits of drone inspections as explained by Kramer include:

• Speed — Once on site, a drone can be deployed in a matter of minutes, and with no need to put clearances or hold orders in place. Depending on what is being inspected, the setup for a rope-access inspection could take several hours in order to ensure safety for the climber and all others involved.

• Agility — Drones have the ability to perform emergency inspections in hard to reach locations or in areas that are unsafe to place personnel.

• Safety — No clearances or hold orders need to be in place to fly a drone for inspections, due largely to the fact that a person is not being placed in an area where injury could occur.

• Cost Savings —Rope-access inspections are expensive, with many basic inspections costing upwards of $10,000 for one site. Drone use is much more cost effective.

Other uses for drones include aerial photography, construction monitoring, monitoring of dam during flood inspections and lock miter gate inspections.

“UAVs enable an engineer or inspector to remotely monitor what the camera is observing,” Kramer explained. “This technology enables TVA inspectors to capture imagery data of dam’s face and gates for current and future reference more safely, efficiently and accurately than traditional methods.”

—FROM STAFF REPORTS

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