USGS hopeful damage at breach won’t hurt farmland
Monday, May 9, 2011
ST. LOUIS (AP) — The land behind the Birds Point levee in southeast Missouri is among the richest in the Midwest, so farmers displaced by last week’s intentional levee breach are understandably worried about what they’ll find when the water goes down. One expert said Monday he is hopeful the damage won’t be as bad as many fear.
The Army Corps of Engineers used explosives on May 2 to blast a massive hole in the levee near the town of Wyatt and allow the Mississippi River to engulf 130,000 acres of land that produces wheat, corn and soybeans. The blast was done in part to save about 1,000 homes in the Illinois town of Cairo. But it destroyed what was expected to be a bumper crop of wheat nearing harvest, and corn and soybeans won’t be planted this year. State and federal agriculture leaders have promised the incident will be treated like a national disaster to help farmers and others with losses.
Still, farmers worry about the land left behind by the ravages of the river. Often when a levee breaches or is overtopped, massive ruts develop in the land and top soil is washed away, making it harder to farm. Also, sand from the river bed washes onto the land, making the rich soil less productive.
The nature of the intentional breach might lessen the impact on land at Birds Point, said Bob Holmes, national flood specialist for the U.S. Geological Survey.
A natural levee breach occurs when the force of the water, often combined with a saturated levee, creates a hole that allows the water in. That hole is typically 500 feet to 1,000 feet wide. Because the river water rushes through a relatively narrow opening, it comes with a high velocity that causes scours and deposits large amounts of sand into the area behind the levee, Holmes said.
“If it’s a small width it’s going to concentrate the flow and the velocity is going to be really high,” Holmes said.
By contrast, the orchestrated explosion at Birds Point created an 11,000-foot-wide opening allowing the water to flow through more gently, Holmes said. For that reason, he is cautiously optimistic damage won’t be as severe.
“I’m hopeful the land will not be damaged as much as we’ve seen in other floodplains where the levee is breached,” Holmes said.
No one will know for sure until the water recedes, and Corps. Maj. Gen. Michael Walsh said last week it could be late summer before that happens.
The Mississippi remains dangerously high throughout southeast Missouri but is going down. The last place to crest was Caruthersville, where the river level topped out at a record 47.61 feet Saturday — about 2.4 feet below the top of the floodwall. The National Weather Service had been expecting a crest of 49.5 feet, and the Missouri National Guard helped build a secondary sandbag levee and earthen berms in case the water came over the top of the wall.
National Weather Service officials weren’t sure why the river stopped rising, though they said the intentional breach at Birds Point probably wasn’t a factor. The crest prediction may have simply been off. Hydrologist Gene Rench said the extreme nature of the flooding and the intentional levee breach made the crest prediction at Caruthersville difficult.
While flooding continues to rage in the south, Rench said the worst of it is over in Missouri, thanks in part to an overdue break in the weather. The southeastern part of the state had more than 20 inches over rain over a two-week period in late April and early May, “but we’re back to normal weather,” he said.