* Lock 27 closed Saturday for repairs, may reopen Thursday
* Closure costs industry an estimated $2.5 mln-$3 mln/day
* 56 vessels awaiting passage Wednesday morning
By Karl Plume
Sept 19 The busiest lock on the Mississippi River remained closed on Wednesday after being shut down for emergency repairs over the weekend, causing a backup of commercial vessels on the crucial shipping waterway, government officials said.
The closure of lock and dam 27, the southernmost lock on the Mississippi River's lock system and just upriver from St. Louis, is estimated to result in some $2.5 million to $3 million in lost revenue each day that it is closed as shipments of grain, coal and other commodities are delayed.
The lock was closed on Saturday after crews discovered damage to one of the lock's protection cells. The cells are rock-filled cylinders which vessels often bump against as they enter the lock.
Low water on the river following the worst U.S. drought in 56 years had exposed an unarmored portion of the protection cell and frequent impacts by vessels caused a breach, allowing some of the rock to spill into the channel and obstruct it.
"Both lock chambers, the main chamber and the auxiliary, are blocked by the rock that came out of the protection cell. Until we can guarantee safe approach there's no traffic moving," said Michael Petersen, spokesman with the U.S. Army Corps of Engineers St. Louis District.
A queue of 56 vessels was awaiting passage as of 11:30 a.m. CDT (1630 GMT) on Wednesday, according to the U.S. Coast Guard.
The Army Corps, which manages the lock system, expects to begin allowing passage of vessels by early Thursday morning at the earliest, Petersen said.
The Mississippi River is the main shipping waterway for grain moving from farms in the Midwest to export facilities at the Gulf of Mexico. Some 55 to 65 percent of U.S. corn, soybean and wheat shipments exit the country via the U.S. Gulf. (Reporting by Karl Plume in Chicago; Editing by Bob Burgdorfer)