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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 Addition 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 as another TVA facility in Muscle Shoals, Ala.
  • Fabrication of the approach wall beams will be completed in 2013.  The approach wall beams are being stored at another TVA facility, Watts Bar Dam.
  • The next contract will begin construction of the lock.
  • The project is not in the president's fiscal year 2015 budget.
  • It is estimated that the project could be completed in approximately eight years with full funding.

Work Accomplished:

Chickamauga Lock Aerial PhotoIn the middle of the photograph is the cofferdam that will be used to dewater the construction area for the new lock.  The cofferdam encloses the work area so that water can be removed and work can be accomplished under “dry” conditions.  On the rear side of the cofferdam is a portion of the new lock wall that was incorporated into the enclosure so that the existing lock could remain open to navigation.  A traditional cofferdam would have blocked access to the downstream end of the existing lock, effectively closing the lock to commercial navigation.  In the background you can see a traffic circle and small bridge that were part of the roadway relocation project completed to clear the way for lock construction.