Chattanooga's river transportation artery will be blocked for nearly four weeks, starting next month, while crews assess and repair the aging Chickamauga Lock.

The U.S. Army Corps of Engineers will remove the water from 360-foot-long lock starting July 20 to inspect the condition of the 70-year-old structure. The planned 27-day closing of the lock is one of three such closings this year at East Tennessee locks, part of the corps' maintenance of the navigation channel for the 652-mile-long Tennessee River.

"Barge operators try to plan their schedules around these lock closings which, fortunately for most locks, come only every five years or so," said Clive Jones, executive director for the Tennessee River Valley Association, a trade group for river users based in Athens, Ala. "In most instances, customers are able to plan ahead and get their shipments early to avoid any disruptions."

Emptying the locks

The U.S. Army Corps of Engineers is "dewatering" its three East Tennessee locks this year for maintenance work

* Fort Loudon near Lenoir City, Tenn., was idled from April 20 through May 11

* Chickamauga Lock in Chattanooga will be idled from July 20 through Aug. 16

* Watts Bar Lock near Spring City will be idled from Oct. 12 through Nov. 2

Source: U.S. Army Corps of Engineers

Chickamauga Lock history

* 1940 -- TVA opens 360-by-60-foot lock through the Chickamauga Dam

* 1970s -- TVA discovers problems with "concrete growth" in the lock chamber

* 1999 -- Army Corps of Engineers assumes control of the lock and begins "aggressive maintenance" of existing lock

* 2003 -- Congress authorizes construction of a 110-by-600-foot replacement lock

* Road and bridge relocations completed and built on the north shore of the lock for construction of the new lock

* 2007 -- Construction of coffer dam begins for new and bigger lock

* 2011 -- Construction of the new lock walls could begin

* 2015 -- Construction could be completed of the new lock, pending funding by the Congress

Source: U.S. Army Corps of Engineers

But the Chickamauga Lock is having to be drained and inspected at least once every three years because of ongoing problems with "concrete growth" at the lock caused by the reaction of the stone in the cement with the surrounding river water, officials said Monday.

Since its original opening in 1940, the concrete in the lock chamber has grown about 12 inches in length and four inches in height, said Doug DeLong, project manager for the Chickamauga Lock maintenance program.

While the corps is building a new and larger lock at Chickamauga, the federal agency is spending nearly $3.8 million this year to install extra anchors and to repair crumbling concrete in the current lock. To help hold the locks and gates in place, the corps has or will install more than two dozen cable anchors secured in the bedrock beneath the lock.

Since 1999, the corps has spent $22 million to inspect and repair the crumbling lock. In the past seven years, the Corps has also spent nearly $200 million to prepare the site and build a coffer dam in which a new and bigger lock chamber will be erected, pending congressional funding.

The corps is trying to keep the existing lock open past 2015 and to secure adequate funding to complete the new lock by then. But construction of the new lock walls won't begin until next year, at the earliest, and then only if Congress is able to secure more money or revamp the funding formula for the project.

The initial $267 million estimate for the new and larger lock has nearly doubled since the project was authorized by Congress in 2003. Additional funding for the project will require more matching funds from the Inland Waterways Trust Fund, which has largely been depleted by more expensive repair projects on the Ohio River, according to Wayne Huddleston of the Corps of Engineers.

In the meantime, companies that rely upon river barge traffic above Chattanooga on the Tennessee River are preparing for next month's dewatering outage and hoping for a long-term fix.

At the Olin chemical plant on the Hiwassee River in Charleston, plant manager Ken Corley said the company is building an inventory of salt from river barges ahead of the July 20 closure of the Chickamauga Lock.

"We might unload barges in Chattanooga and truck salt to our Charleston plant and we also could receive salt by rail," Mr. Corley said. "Both alternatives will increase our costs."

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