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A cofferdam is a temporary watertight enclosure from which water is pumped to expose normally immersed areas.  It is used during construction of navigation locks to be able to construct lock walls in a dry area.

Chickamauga Lock Replacement Project

Chickamauga Lock Addition ProjectChickamauga Navigation Lock, seven miles upstream of Chattanooga, Tenn., at river mile 471, is owned by the Tennessee Valley Authority and operated by the U.S. Army Corps of Engineers.  Upstream of Chickamauga Lock are 318 miles of navigable waterway used to transport materials to and from industries, TVA facilities and the Department of Energy facilities at Oak Ridge.  A concrete aggregate problem causes structural concerns at the existing lock, and will result in closure of the lock at some point.  Also, the existing 60-foot by 360-foot lock is a non-standard size that is not suited to the barges used by the transportation industry today.  The new 110-foot by 600-foot Chickamauga Lock, designed and constructed by the U.S. Army Corps of Engineers Nashville District, will replace the existing lock, improve locking efficiency, and solve the structural issues caused by the concrete aggregate at Chickamauga Lock.

Project Abstract:

  • Without aggressive maintenance a concrete aggregate problem will cause the current lock to be closed.
  • Construction was initiated in summer 2007, and a Road and Bridge Relocation contract ($16 million) was completed in fiscal year 2007.
  • Lock design was completed in 2009.
  • Cofferdam construction and fabrication of the miter gates, culvert valves and culvert bulkheads were completed in 2012.  The miter gates, culvert valves, and culvert bulkheads are stored off site at another TVA facility in Muscle Shoals, Ala.
  • Fabrication of the approach wall beams was completed in 2012.  The approach wall beams are being stored at another TVA facility, Watts Bar Dam.
  • After a three year temporary suspension of construction activities, due to funding constraints, a contract to place grout along the perimeter of the existing cofferdam was awarded in September 2015.  The grouting was intended to cut-off water seepage paths, which will help to keep the work area inside the cofferdam dry during future contracts.  This contract was physically completed in July 2016.  
  • The approximately $35 million Lock Excavation contract was awarded in September 2016 to accomplish the majority of the required rock excavation prior to placing concrete for the new lock; this contract was substantially completed in January 2019.
  • The follow on $240 million Lock Chamber construction contract was awarded in September 2017 and will last between five to seven years depending on annual funding amounts.  This contract will construct a functioning lock chamber inside the cofferdam; however, the lock will not go into operation until the dam and cofferdam are breached, which will occur in the next construction contract to construct the approach walls and decommission the existing lock. 
  • The project is not in the president's fiscal year 2019 budget.
  • It is estimated that the project could be completed as early as December 2024 with efficient annual funding.

Work Accomplished:

This photograph shows the lock excavation progress inside the cofferdam as of November 2018.  The lock excavation contract removed approximately 100,000 cubic years of rock to prepare the foundation of the new lock structure.  In the top left portion of the photo in the newly constructed on-site concrete production facility that is part of the $240 million Lock Chamber contract.  All concrete for the new lock will be mixed on-site and deliver to the cofferdam work are by elevated conveyor system that will be installed in 2019. The Lock Chamber contract includes a base with 13 contract options; the base and four options valued at $95.7 million have been exercised as of the end of Fiscal Year (FY) 2018.  The project received $89.7 million through the FY 2019 Work Plan, which will be used to exercise four additional Lock Chamber contract options.