* Some grain elevators unable to load barges as water rises
* Grain prices up on supply concern, reopen date uncertain
* Most locks from 12 to 24 to close as floodwaters swell
By Karl Plume
June 25 (Reuters) - Rising water on the Mississippi River will force the U.S. Army Corps of Engineers to close numerous locks on the major shipping waterway for the second time this month, from central Iowa to central Missouri.
The river is already above flood stage at numerous locations following recent heavy rains and more precipitation is in the forecast for the region.
The river is the main barge shipping channel for moving grain from Midwest production areas to export terminals at the Gulf Coast. Some 60 percent of all U.S. grain exports are shipped via the Gulf.
Corps engineers, who manage locks and dams throughout the inland waterways system, have to remove critical lock operating equipment when the river gets too high.
Lock 12 near Bellevue, Iowa, was expected to close early on Thursday, along with locks 16 and 17 further downriver, said Army Corps Rock Island District spokesman Ron Fournier. Locks 13, 18, and 20 through 22 were forecast to close between June 29 and July 2, he added.
At Lock 24 in Clarksville, Missouri, the river was expected to hit the lock closure stage around July 4 or 5, said Michael Petersen, St. Louis District spokesman for the Corps.
Neither had a reliable forecast for reopening the locks due to unpredictable weather.
The rising river also prevented some grain elevators in the flooded areas from loading grain barges, because the vessels were unable to get under the loading spout that hangs above the river.
Fears that the shipping disruptions may persist raised prices for spot barge loads of corn and soybeans at the Gulf Coast by 7 to 10 cents per bushel on Tuesday.
(Editing by Dan Grebler)