(Recasts, adds details of Mississippi River accident, adds closure on lower Ohio River, adds quote, adds byline)
By Karl Plume
April 7 (Reuters) - Two separate barge accidents halted navigation on the flood-swollen Mississippi and lower Ohio rivers on Friday, severing the flow of grain from the upper Midwest to export terminals along the Gulf Coast, government officials said.
A section of the Mississippi River was closed to navigation on Friday morning after nine grain barges broke free from a tow and struck lock and dam 22 near Saverton, Missouri, north of St. Louis, the U.S. Army Corps of Engineers said.
The river will be closed until at least 8:00 pm CDT on Friday (0100 GMT Saturday) to allow the Corps, which operates the dam, to assess damages and begin recovery operations.
"We won't know for a couple of days the extent of the damage or if there is damage," said Allen Marshall, spokesman for the Army Corps' Rock Island district.
It is unclear if the swift current contributed to the accident or whether there was another cause.
Separately, the Coast Guard has closed a four-mile (6-km)stretch of the lower Ohio river near Brookport, Illinois, on Thursday after a tow boat pushing 19 empty barges and one loaded with steel struck lock and dam 52 and began taking on water.
The vessel, owned by American Commercial Barge Line, had about 47,000 gallons of diesel on board, but no pollution has been reported, the Coast Guard said.
A queue of nine upriver bound vessels and seven downriver bound vessels was waiting to pass on Friday morning, the Coast Guard said.
Several days of heavy rain in the Midwest have swelled waterways above flood stage in much of the region, forcing shippers to limit the number of barges they haul in each tow or sideline vessels altogether due to swift currents, grain shippers said.
The river closures halted movement of grain barges from a large portion of the Midwest farm belt to Gulf Coast export terminals, which handle about 60 percent of U.S. corn, soybean and wheat export shipments.
Corn costs at the Gulf rose by about 2 to 3 cents per bushel, partly in response to the slowed flow of grain, grain traders said. (Reporting by Karl Plume in Chicago; Editing by Marguerita Choy)