Amber Colbert, 15, lifts a sandbag up as she and her family prepare for rising flood waters due to the opening of the Morganza Spillway in Stephensville, Louisiana May 15, 2011. [Photo/Agencies]

AMELIA, La. - A day after US Army engineers opened a key spillway to relieve flooding along the Mississippi River, residents of small Louisiana towns braced on Sunday for a surge of water that could leave thousands of homes and farms under as much as 20 feet (6 meters) of water.

The US Army Corps of Engineers on Saturday opened two of the 125 floodgates at the Morganza Spillway 45 miles (72 km) northwest of Baton Rouge, and opened two more on Sunday.

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Opening the floodgates - a move last taken in 1973 - will channel water away from the Mississippi River and into the Atchafalaya River basin. That will take the floodwaters toward homes, farms, a wildlife refuge and a small oil refinery but avoid inundating New Orleans and Louisiana's capital, Baton Rouge.

In towns like Amelia, about 100 miles (160 km) south of the spillway, crews worked around the clock to build earthworks and reinforce levees ahead of a torrent of water expected to reach the area on Monday or Tuesday.

"I hope they know what they are doing," said Hue Tran, watching the giant dump trucks from the Quik General food store, a short distance from the intercoastal waterway.

Weeks of heavy rains and runoff from an unusually snowy winter caused the Mississippi River to rise, flooding 3 million acres (1.2 million hectares) of farmland in Mississippi, Tennessee and Arkansas and evoking comparisons to historic floods in 1927 and 1937.

Louisiana towns in the path of the floodway like Krotz Springs, Butte LaRose and Morgan City are making similar plans for severe flooding that could last for three weeks before the water works its way to the Gulf of Mexico.

In Krotz Springs, which will be among the first towns to feel the flood's effects, Kathy Reed-Eason spent the weekend moving her parents' belongings out of harm's way.

"My mom was crying," Reed-Eason said. "Mom said she'd go look at the river, and get out of the house."

About 2,000 people were ordered to evacuate from St. Landry Parish, just south of Krotz Springs.