The replacement of the deteriorating Chickamauga Lock will be a massive project that will require the excavation or dredging of approximately 123,000 cubic yards of substrate and the blasting and removal of approximately 181,000 cubic yards of rock, Army Corps of Engineers officials said.
A public notice says all of the excavated material will be disposed of off-site in accordance with local ordinances.
Construction of the lock will require almost 300,000 cubic yards of concrete, 31,1214 cubic yards of gravel fill, and a variety of
precast beams, rebar, and other components. These materials will
be used to construct the lock itself.
An estimated 26,390 cubic yards of riprap would be placed along the shoreline along the channel modification, and most will be above ordinary high water.
The stone will range in weight from a minimum of 86 pounds to a maximum of 300 pounds and will be obtained from
a clean, native source, officials said.
The report says Chickamauga Lock is experiencing structural problems resulting from alkali aggregate reaction (AAR). AAR is a reaction between the alkali in the cement and the rock aggregate, which results in a physical expansion of concrete
structures. This expansion of the concrete threatens the structural integrity of the lock and has created an unsafe condition in the lock, it was stated.
It is no longer economically feasible to continue to repair Chickamauga lock, the report says.
The proposed work consists of constructing a 110 x 600 foot or a
75 x 400 foot lock at Chickamauga Dam. The proposed lock would be
located on the riverside of the existing lock and downstream of
the existing dam. The downstream
location would allow use of the existing spillway dam as an upstream water barrier during construction of the new lock.
The riverside location for the new lock would cause the loss of four
spillway bays, eventually requiring the removal of four gates and a portion of three concrete piers. Part of the downstream approach wall to the existing lock also would be removed.
To provide a downstream water barrier during construction, a sheet pile cofferdam connecting the dam and existing lock would be constructed. A temporary bascule-type drawbridge would be constructed across the lower approach to the existing lock to
provide access to the new lock construction site within the cofferdam. After the cofferdam is removed, the bascule bridge
would be relocated to provide a permanent access bridge to the new
lock.
Upstream and downstream approach walls, 800 feet in length, would be built on the spillway side, with the downstream approach wall extending under and through the Norfolk Southern
Railway Bridge.
Approximately 3,200 feet of the navigation channel would be widened immediately downstream of the existing
Chickamauga Lock. Two new 30 foot diameter mooring cells would be
built downstream of the new lock.
The Highway 153 bridge across the lock would remain open during construction, and Lake Resort Drive would be relocated. As part of the relocation of Lake Resort Drive, two new bridges would be built, one over North Chickamauga Creek and one for grade separation between Lake Resort
Drive and the permanent access road to the North Chickamauga Creek
Greenway.
After the new lock is completed (or sooner if conditions dictate)
the existing lock would be closed to navigation. This action would make the structure a safe water barrier. Once the lock was closed, a portion of the lock chamber and the associated wall culverts would be plugged with concrete. The upper and lower mitre gates would be removed. Post-tensioning would strengthen
walls, and wider slots would be cut in the approach walls to prevent problems from continued concrete growth. No cofferdams would be required; however, installation of needle dams (similar to a cofferdam but more temporary) and dewatering of the chamber would be required.
A Final Supplemental Environmental Impact Statement FSEIS has been prepared to document anticipated impacts of the work.
Copies of the FSEIS may be obtained by writing to: U.S. Army Corps of Engineers, Planning Branch, Attention: Wayne Easterling, PO Box 1070, Nashville, TN, 37202-1070, or by calling Mr. Easterling at (615) 736-7847.
All of the construct new lock alternatives include a downstream
approach wall that would extend beyond the Norfolk and Southern
Railroad Bridge. In addition, at least one of the support piers of the bridge would be surrounded or wrapped by metal sheet pilings to protect it from inadvertent collisions by barges. The National Register eligibility of the bridge has not been
evaluated.
Although the actual structure of the bridge will not be directly affected by the approach wall construction, the visual context of the bridge will be affected. An evaluation of the
National Register eligibility of the bridge and an assessment of adverse effect will be required before a Record of Decision can be signed.
Resulting work will adversely affect properties that are eligible for listing in the National Register of Historic Places. The Advisory Council on Historic Preservation has been notified and the Tennessee State Historic Preservation Officer (SHPO) is being consulted to determine how such adverse effects can be taken into
account by avoidance, minimization, or mitigation.
Due to the presence of prehistoric archaeological remains, consultation with Native American Tribes has been initiated. In accordance with requirements at 36CRF § 800.6, the Corps of Engineers proposes to address the adverse effects of lock replacement within the context of a Memorandum of Agreement (MOA) amongst the Corps of Engineers, the Tennessee Valley Authority, and the Tennessee
State Historic Preservation Officer.
The MOA will stipulate 1) measures that will be implemented to avoid, minimize, or mitigate potential adverse effects on historic properties including the Chickamauga Lock and Dam complex and other potential historic properties, including archeological sites, 2) requirements for additional archeological survey and testing, and 3) requirements for archeological monitoring during certain aspects of
construction.