The Interstate 20 bridge across the Mississippi River was expected to be shut down for at least two hours starting at about 2 p.m. today as salvage crews attempted to lift a barge that sank near a support pier Wednesday after a 30-barge tow broke apart in the river’s flood-swollen water.

“We’ve been in touch with the U.S. Coast Guard, the Mississippi Highway Patrol, the Mississippi Department of Transportation, the Louisiana Department of Transportation and the Louisiana State Police,” Sheriff Martin Pace said of he and Vicksburg Police Chief Walter Armstrong. “Safety engineers don’t need any traffic on the bridge during the salvage.”

The closing of the bridge was contingent on salvage operators being able to perform the task today, Pace emphasized.

The Louisiana State Police predicted in a news advisory at 11 a.m. the bridge would be closed for two hours.

The grain-filled barge was one of the 30 being pushed south on the river by the Kay A. Eckstein at about 2:25 p.m. when a line of barges struck pier 3 of the old U.S. 80 bridge. The tow scattered and two of the barges hit the Interstate 20 bridge, where one was hemmed against a support pier by swift current for two hours before it broke apart and sank. A second barge that sank near Baxter Wilson Steam Electric Generating Plant was recovered after nightfall.

Wednesday’s strike was the second in four days at the bridges. Early Sunday, a 25-barge tow headed north and pushed by the Joshua David Esper hit pier 5 on the older bridge, causing surface damage and prompting a daytime-only limit on river traffic. Paducah, Ky.-based Marquette Transportation Company owns both vessels. No injuries were reported in either strike.

About 26 miles of the river south of the bridges were off-limits to barge traffic as investigations into both strikes continued, said Lt. Teresa Hatfield, supervisor of the U.S. Coast Guard Marine Safety Detachment in Vicksburg, adding a few barges contained beans and coal. She said 12 southbound tows upriver from Vicksburg and six northbound are on hold while restrictions are in effect.

Ergon Marine’s fleet recovered and collected all of the scattered barges downriver near Riverwalk and Rainbow casinos and along the riverbank. Six were held together this morning south of the city, near LeTourneau Technologies.

Wednesday’s strike of the U.S. 80 bridge was not unlike similar hits over the past few years when the river rose during spring snow melts farther north, but it was the first time the I-20 bridge has been reported hit.

“I felt it very strongly,” said U.S. 80 bridge superintendent Herman Smith of the initial jolt. He was in his office, on the east end of the bridge.

He said the hit creates “a major issue” because support pins at the top of the pier broke with the force of the strike.

A preliminary assessment Wednesday night by Baton Rouge-based G.E.C., the bridge’s structural engineering firm, showed damage on three piers to I-bars that hold the superstructure down while trains pass, Smith said. A repair estimate was forthcoming. The broken pins are part of the same support structure on pier 3 where bearings were replaced and other cracks were repaired last year at a cost of $637,754. An annual stability inspection for 2010 completed by G.E.C. rated the 81-year-old span in “fair-to-very good condition.”

While preliminary inspections of the I-20 bridge were made Wednesday afternoon, motorists were detoured for two hours.

Today, Engineers with the Louisiana Department of Transportation & Development planned an in-depth inspection of the highway bridge’s E1 support pier, said T. Marshall Hill, District 5 Engineer administrator. A visual inspection of the bridge and analysis of its balance sensors turned up no significant damage, Hill said.

The Mississippi River level at Vicksburg this morning was 42.1 feet, up a half a foot in 24 hours. Forecasters expect the river to crest at Vicksburg’s 43-foot flood stage Tuesday, bringing the third official river flood here in four years.

In 2008, stages topped out at 50.9 feet, the highest in Vicksburg in 35 years. Five barge tows struck the U.S. 80 bridge between March 26 and May 3, the first four of them coming in 10 days. In 2009, the bridges survived the river’s spring crest of 47.5 feet without a barge strike, reportedly due to slower currents. The last barge strike was to pier 4 on March 22, 2010, a year and a day prior to Wednesday’s strike.

Drain valves remain shut at three locations on the city’s floodwall. Additional closures to prevent water from the Yazoo Diversion Canal from seeping under the wall aren’t planned by the city Sewer Department unless current crest predictions are changed.

Northwest of the city, Chickasaw, Long Lake, Laney Camp and Ziegler roads were closed due to high water. Backwater flooding has inundated farmland along Chickasaw and Long Lake.

The Kings Point Ferry is out of service until further notice, and the vessel is docked at the Port of Vicksburg. Jackson Lane, which dead-ends into brush in Kings, is expected to take on water when the stage hits 43 feet.

Eagle Lake was at 76.46 feet this morning, up six one-hundredths of a foot. The Muddy Bayou Control Structure is open and is expected to bring the lake’s stage up to 76.9 feet over several days.

Levels on the river side of the Steele Bayou Water Control Structure on Mississippi 465 stood at 89.8 feet, up three-tenths of a foot. The land side held at 85.4 feet overnight.

Crests are forecast for March 30 on the land side near 86 feet and 91 feet on the river side.