* Spot CIF corn basis 10 cts over futures, lowest since 2009
* Corn supplies rise as harvest, barges backing up at Gulf
By Karl Plume
Sept 6 (Reuters) - Cash premiums for spot corn barges at the U.S. Gulf Coast plunged to a near-three-year low this week as newly harvested supplies were piling up at export terminals which have yet to recover fully from Hurricane Isaac, trade sources said.
Some grain export houses which sustained only minimal damage from the category 1 storm that came ashore near New Orleans last week expected to resume normal operations by the end of the week but others may remain offline for longer, they said.
Meanwhile, rains from the storm have raised the water level on the Mississippi River, allowing more grain to be shipped to the Gulf after weeks of restricted traffic due to low water on the major shipping waterway.
"Corn barges are stacking up at the Gulf," a barge trader said. "They're running bigger tows now with the rain we've had and the (storage) space down there is pretty much filled up."
September-loaded corn barges shipped to the Gulf Coast, including insurance and freight, traded late on Wednesday as low as 10 cents a bushel over Chicago Board of Trade December futures and were lightly bid at similar prices on Thursday. That was down nearly 30 cents from bids earlier in the week and the lowest spot basis values since December 2009.
The market was pressured by ample supplies of corn at the Gulf as the U.S. harvest was well underway and much of the crop from the southern United States was flowing to the export market.
Exporters have been unable to load ocean-going vessels for more than a week so, with little to no elevator space to store the corn, much of the arriving grain would need to be stored in barges on the water, incurring demurrage charges.
The already-slow pace of export shipments stalled last week as Isaac forced the closure of grain elevators and other facilities for several days. Many of those facilities were struggling to return to normal operations due to flooding and power outages in the wake of the storm.
Agribusiness giant ADM, which has four terminals at the Louisiana Gulf, said on Wednesday that its facilities sustained some damage from wind and rain but a return to normal operations was expected this week.
Other elevators, including the southernmost grain house owned by CHS, were taking longer to come back online, trade sources said.
In the week ended Aug. 30, only 3.46 million bushels of corn were inspected for export at the Gulf, compared with 17.27 million bushels in the same week a year earlier, according to U.S. Department of Agriculture data. (Reporting by Karl Plume in Chicago; Editing by Tim Dobbyn)