* Isaac rains raise water levels on lower Mississippi
* 10-foot barge drafts allowed, up from 9 feet
* Extra foot of draft allows about 200 tons more cargo
* Other shipping restrictions remain in place
By Karl Plume
Sept 4 (Reuters) - Barge draft restrictions on the lower Mississippi River were eased slightly this week as heavy rain from Hurricane Isaac replenished the drought-depleted waterway and allowed shippers to transport heavier-loaded barges.
But the storm's benefits may be short-lived as water levels on much of the river remained near historic lows and more rain was needed to maintain the river's depth following the worst U.S. drought in more than a half century.
The U.S. Coast Guard updated its safety advisory on Monday for the lower Mississippi to allow barge drafts of 10 feet, still below normal drafts of 12 feet or more but up from the 9-foot limit that had been in place for more than a month.
The one-foot increase in draft allowed shippers to load each barge with an additional 200 tons of cargo.
Barge tow sizes remain restricted to no more than 25 barges for southbound tows and 36 barges, up to 20 of them loaded, for northbound tows, the Coast Guard said. Barge tows normally contain 40 barges or more on the lower Mississippi.
The advisory, for traffic between river mile marker 869 near Tiptonville, Tennessee, to mile 303 near Louisiana's northern border, will be updated on Wednesday, the Coast Guard said.
A two-mile safety zone remained in place near Greenville, Mississippi, from mile marker 524 to 526 due to low water.
The river was also closed temporarily between mile markers 696 and 698 about 30 miles south of Memphis for dredging by the U.S. Army Corps of Engineers.
Further south, a stretch of the river from Baton Rouge, Louisiana, to the Gulf of Mexico that was closed for three days last week due to Hurricane Isaac was reopened late last week with no restrictions.
The Mississippi River is the main U.S. grain shipping channel connecting farms in the Midwest with export terminals at the Gulf Coast. Some 55 to 65 percent of U.S. corn, soybean and wheat exports exit the country via the Gulf Coast. (Reporting by Karl Plume in Chicago; Editing by Phil Berlowitz)