* 12-hour daily closures from Grand Tower to Thebes, Ill.
* Work to be completed in about 10 days
* Rock removal project to deepen shipping lane by 2 feet
By Karl Plume
Jan 29 (Reuters) - The U.S. Army Corps of Engineers will begin removing riverbed rock obstructions from the Mississippi River near Grand Tower, Illinois, on Tuesday night in the final phase of a project aimed at keeping the drought-hit shipping artery open to barge traffic.
The river will be closed to navigation daily from midnight until noon between Grand Tower and Thebes, Illinois, 31 miles downriver, where the Corps has been blasting and removing rock pinnacles since mid-December, the Corps said on Tuesday.
Closures had previously lasted 16 hours each day.
About 64 cubic yards of rock which pose a risk to navigation during periods of low water will be removed from the riverbed at Grand Tower over roughly the next 10 days, the Corps said.
The remaining work at Thebes, including removal of a previously undiscovered rock formation slightly downriver from the original work zone, could conclude by the middle to end of next week, a spokesman said.
"Once this rock work is complete and the dredging wraps up, it's going to give us two additional feet of depth to work with during low water operations," said Corps spokesman Mike Petersen.
The rock clearing project, the Corps' largest such undertaking in at least 25 years, was fast-tracked by the federal government as the Mississippi River neared historic lows amid the worst U.S. drought in a half century.
The Corps is congressionally mandated to maintain a 9-foot-deep channel for river navigation.
Shippers rely on the inland river system to haul billions of dollars in grain, coal, fertilizer and other commodities every year, including some 55 to 65 percent of U.S. corn, soybean and wheat exports that exit the country via the Gulf Coast.
(Reporting by Karl Plume in Chicago; editing by Matthew Lewis)