Thursday, May 12, 2022

1952 114mwNet TVA Boone Dam on South Fork Holston River near Spurgeon, TN

(Satellite)

The dam is 160' high and 1,697' long. The height of the reservoir normally varies 25' between summer and winter. Three units are used to generate 114mwNet. [TVA-energy

0:07 video @ 0:00
A great view of sluicing at Boone Dam. Our generators are undergoing reliability maintenance in preparation for our full return to operations this summer with the completion of the Boone Dam project. #BooneDam #BooneRepair pic.twitter.com/ecXBoEHEvQ
— TVA Boone Dam Repair (@BooneRepair) March 31, 2022

But between 2015 and the Spring of 2022, the water level was kept 10' below winter level while the dam was being repaired. [TVA-project] Once again, the TVA has demonstrated that it is challenging to  build a dam on top of a cave system. "During construction of Boone Dam, workers encountered voids and soft muddy soils in part of the ground called the “epikarst.” To limit groundwater seepage under the dam, engineers created a deep “cutoff trench” to remove the voids and soft soils and pumped grout into the foundation to fill any remaining voids—a state of the art foundation treatment in the 1950s. During an inspection in October 2014, TVA discovered a sinkhole near the base of the embankment at Boone Dam. Further study revealed deterioration of the cutoff trench, allowing seepage flows that continue to undermine the foundation of the dam. TVA is currently in the process of fixing the problem." [TVA-history]

"In 2014, the Tennessee Valley Authority discovered a sinkhole at the base of Boone Dam’s earthen embankment and muddy discharge in the river channel below the dam, both of which were signs of internal erosion. The agency said it’s still on track to complete the project in July 2022, which is within the 5-7 year timeline TVA initially outlined when it began repairs in 2015....As a rough estimate, Saucier said the total cost of the project is now about $300 million, less than $400 million budgeted for repairs." [JohnsonCityPress]

Google Earth, May 2022, facing South

The Problem via TVA-project

The composite seepage barrier consisted of two components constructed in a three-stage process:

  • Stage 1: Grout curtain in the foundation soils and epikarst
  • Stage 2: Grouting the underlying bedrock
  • Stage 3: Concrete diaphragm wall through the dam and epikarst terminating in the underlying bedrock

The remediation approach was similar in concept to those used in other dams with karstic seepage issues in Kentucky and Tennessee, such as Wolf Creek Dam and Center Hill Dam.

[TVA-project]


The Solution via TVA-project

They also built new boat ramps and beaches 35' below the normal summer water level so that the lake could still be used in the summertime during the repairs. And they added a bunch of buoy markers to mark hazards introduced in the lake because of the lower water level.

TVA posted four photos with the comment: "Divers remove bolts from the large steel bulkheads that cover the outlets from Boone Dam Unit 1, which has been out of service since the start of the dam's repair project. The unit will soon return to service, producing low-cost hydropower. Boone Dam has three generating units with a capacity of 114 megawatts."
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