TVA Handles Debris From Heavy Rains At Dams
Thursday, March 7, 2019
Amid the wettest February in recorded history, the Tennessee Valley Authority held back more than 3.5 trillion gallons of water to help prevent over $1.6 billion in flood damage across the Tennessee Valley in February.
Despite those damages averted, the raging waters and record rainfall caused extensive erosion along Tennessee River banks. Also, the rising water in the system washed tons of debris onto shoreline properties, recreation areas and even into TVA dams.
Trees, logs, docks, trash and other debris were torn away and washed miles downstream, scouring and littering shorelines and clogging trash gates at some TVA dams.
The deluge of debris impacted or threatened generation at several TVA dams, including Wheeler, Nickajack, Great Falls and Pickwick at a time when massive amounts of water were being pushed through the dams to prevent flooding. For example, Pickwick Dam was releasing 4 millions gallons per second at its peak flow.
TVA crews including Hydro Operations, Dam Safety, and River Management worked together 24/7 to overcome any debris disruptions and to manage the river, protect Valley residents and their property, and to provide reliable power throughout the deluge.
“We had to briefly stop generation at some dams because of the huge amount of debris coming downstream,” said Stacey Parrott, general manager for Hydro Generation. “We worked with crews from across TVA to keep the gates clear, clean out excessive accumulations and address any issues created by the debris to keep our turbines working throughout this event.”
TVA’s Dam Safety team continue to be busy conducting inspections at several sites to make sure all the dams, spillway gates and other mechanisms were performing properly in the face of the massive hydraulic force generated created by February’s record high water levels and the huge amounts of water flowing through them.
“Our electrical and mechanical equipment worked reliably during the peak periods, with minimal issues,” said Jennifer Dodd, general manager of Dam Safety. ”A number of systems were called upon at critical times to perform under some of the most adverse conditions we’ve ever seen, and they all operated as designed.”
Dam safety inspections related to the recent heavy rains are still underway and will continue until heavy rains, lake levels and river flows subside.
“The inspections group will have to wait until spilling operations have stopped or slowed substantially before we can safely access the areas below most of the dams,” Dodd said. “We will be looking for evidence of scour and other issues utilizing all the tools we have.”
Ben Phillips, manager of Dam Safety Inspections, said TVA technology such as side scan sonar will be instrumental in evaluating spillway aprons in an efficient manner, Phillips said.
“We can get a look at a spillway in a few hours per dam using sonar compared to a few days or weeks per dam using divers, with less safety risk,” Phillips said.
TVA has contingency plans for all its dams in the event of emergencies such as severe weather like the recent record rainfall, and works closely with emergency management teams to prepare for these events. TVA also has spent about $400 million since 2010 on Dam Safety.
In addition to inspections after severe rain events, TVA also performs monthly, biannual and annual inspections of its hydro facilities to identify any potential issues or concerns and detailed, thorough investigations every 5 years. The inspections also include continuous electronic monitoring for vibrations, and rigorous structural and geological assessments.