A revised Mississippi River forecast offered a bit of a reprieve for shippers Wednesday, showing the water level isn't dropping as quickly as feared.

Months of drought have left the Mississippi near historic low levels, a problem worsened last month when the U.S. Army Corps of Engineers reduced the outflow from an upper Missouri River dam, lessening the amount of water that drains into the Mississippi where the rivers converge near St. Louis.

The river at St. Louis on Wednesday was about 13 feet deep. The Coast Guard has said further restrictions on barge traffic -- most notably in a 180-mile stretch between St. Louis and Cairo, Ill. -- are likely if the river dips to around 9 feet, though the decision is based on observation of conditions and not the level on the gauge.

Earlier National Weather Service forecasts had projected getting to the 9-foot level by Sunday or Monday. But a Weather Service hydrologist told The Associated Press on Wednesday that revised modeling now calls for reaching that level around Dec. 29, then dropping another foot by Jan. 2.

In less than a month, crews will begin blasting to remove rock formations in the Mississippi that threaten barge traffic thanks to low water levels.

David Gordon, chief of the hydraulic design section of the U.S. Army Corps of Engineers St. Louis District said the time frame for the work has been pushed forward after U.S. senators pushed the Corps of Engineers to keep the dwindling river open to barge traffic.

"Work will begin Jan. 3 if not sooner," Gordon said. "We're giving the contractors 60 days to complete the job. But we don't think it will take that long."

Gordon said barge traffic will have to be stopped for 12-24 hours at a time so the work can be done near Thebes, where the Mississippi has a rock bottom.

The first stage of the work will remove rock that will be only 7 feet below the surface if the water reaches the predicted low of about 6 feet below gauge.

About 890 cubic yards of rock are expected to be removed at a cost of $1 million to $5 million.

Later another 6,000 cubic yards must be removed to lower the bottom. Gordon said a cost estimate for that work has not yet been determined.

This isn't the first time the Corps of Engineers has tried to solve the rock problem near Thebes, about 125 miles south of St. Louis.

During a drought in the late 1980s, workers removed rock. But technology at the time didn't allow the job to be done as thoroughly as it can be done now.

The low water on the river has already started to cause problems for barge tows even though it is not nearly as bad as it is expected to get.

A grounded tow blocked traffic Tuesday night about 25 miles south of Memphis, Tenn.

According to the U.S. Coast Guard, a tow with 18 barges got stuck because of low water conditions on the river and caused 35 other tows -- 23 headed south and 12 headed north -- to be delayed.

So far there have been no cases of barges running aground between St. Louis and Cairo, where U.S. Army Corps of Engineers has been working to dredge the river to try to keep the channel open.

Contact reporter Scott Wuerz at swuerz@bnd.com or call 618-239-2626.