updated 8/15/2008 10:28:19 AM ET 2008-08-15T14:28:19

Low water levels on the Mississippi River are causing problems, just weeks after one of the worst floods ever on Ol' Miss.

Twice this week, tows pushing barges on the Mississippi north of St. Louis have become stuck in dirt and sand in the navigation channel. That's partly because the massive flooding in June washed ton after ton of sand and soil into the river.

But it is also because portions of the Midwest have seen very little rain in the weeks since the flood. The river level is dropping up to a foot a day in some areas, said Lt. Rob McCaskey of the U.S. Coast Guard office in St. Louis.

"When you go from extreme high water to low water, that has a tendency to leave behind significant sediment, and it shifts channels unexpectedly," McCaskey said.

The low water is causing concerns for the federal agencies responsible for the river, the Corps of Engineers and the Coast Guard, as well as tow operators. It is estimated that about 60 percent of the nation's agricultural commodities eventually exported overseas are shipped down the river to New Orleans.

The change in river levels has been stunning. At Keokuk, Iowa, the Mississippi peaked at 26.9 feet on June 17, 10.9 feet above flood stage. By Thursday, it was at 4.2 feet. At St. Louis, the river reached 38.7 feet on July 1. Flood stage is 30 feet. It now stands at 8.4 feet.

At Alton, Ill., the river on Thursday was at 6.9 feet, with the National Weather Service projecting it to drop to 5.2 feet by Aug. 21. Flood stage is 21 feet, and the river at Alton reached 33.1 feet on June 30.

The tow Bruce Hahn, with 15 barges, became grounded near Alton Thursday morning. Calls to the tow operator were not returned.

The other incident happened Tuesday when another 15-barge tow got stuck near Winfield, Mo., where dozens of homes were damaged or destroyed after a levee broke on June 27. Neither the Coast Guard nor the Corps of Engineers had information on the name of the barge, which was freed Wednesday.

The Coast Guard closed the river to barge traffic near Winfield, though it is evaluating each tow that arrives and letting some through.

Corps spokesman Alan Dooley said it is common for the river level to drop in late summer. Still, he said this year's extremes have created a difficult situation.

"When you have a flood you get a combination of sediment and soil coming off the farm fields and golf courses and streets and yards," Dooley said. "Also, the energy from the flow picks up sand off the bottom of the river. It swirls it all together in this milky, hazy mixture that comes down the river during flooding."

But as the river level begins to drop, the waters calm. That's when the soil and sand sink to the bottom of the river, clogging the navigation channel with a new and higher floor.

The Corps plans a massive dredging operation beginning Friday, starting at the site near Winfield where the tow was grounded. Corps vessels and contractors will survey the river, mapping the bottom contour, and dredge the trouble spots. The goal, Dooley said, is to keep the navigation channel to at least the prescribed minimum — 9 feet deep and 300 feet wide.

Dooley said the corps is also considering raising the river level north of Winfield by temporarily reducing the flow of water through the dam near the town.

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