URBANA, Ill. — Not quite a year ago, federal officials faced a tough decision: Should they explode part of the Birds Point Levee to ease record flood threats against Cairo, Ill., and other areas upstream, or let the swollen Mississippi and Ohio rivers flow without intervention?

And if the U.S. Army Corps of Engineers didn’t breach the levee on May 2, would Mother Nature spare some 133,000 acres of prime farmland within the Birds Point-New Madrid Floodway in the Missouri bootheel?

The answers, to University of Illinois researcher Ken Olson, seem obvious: The Corps made the right decision to breach the levee because it saved the city of Cairo from significant flooding in town. Had no action been taken, the rich farmland to the south likely would have been flooded to the extent it was anyway, Olson concludes in a recently published article.

He based his conclusion on the fact that the river peaked at Cairo at 61.72 feet on May 3, 2011; the height of the Birds Point Levee fuse plug at 60.5 feet suggests the Mississippi would have topped the levee had it not been exploded the night before.

It’s not a conclusion that sits well with some farmers in the floodway, which hadn’t flooded since 1937. They maintain in a class-action lawsuit that the Corps overstepped its authority and opened the floodway without up-to-date easements to the land.

Nearly $50 million in crop insurance payments were issued as a result of the disaster last spring, which saw record flooding across the Midwest because of a heavy snowmelt in April and excessive local rainfall.

“If you’ve seen Cairo, and you drive through Cairo, you know what’s there, and it’s not much,” said Roy Presson, who farms about 2,300 acres in the floodway. “I’m not sure they made the right decision, given everything that was lost here (in Missouri).”

Olson’s research, published in the January/February and March/April 2012 issues of the Journal of Soil and Water Conservation, concludes that had Cairo’s seawall and levee system failed, about 22 feet of flood water would have inundated the city and surrounding area.

About 600 buildings would have been flooded in Cairo, Future City and nearby Urbandale, and “significant” loss of life likely would have occurred. Olson noted Cairo sits on a “sliver” of land about two square miles in size, and was “surrounded by 30 square miles of water.

“Had the Corps not opened the floodway and let Cairo get filled with water, it would not have prevented the damage to agricultural lands and crops to the south. The floodway would have been flooded anyway since the Mississippi was 1.22 feet higher on May 3 than the Birds Point frontline fuse plug. There was that much floodwater,” Olson said.

“Cairo levee failure was a real possibility because there was a serious sand boil situation on the earthen levee. Floodwaters were starting to put significant pressure on the Cairo seawall and levee system with some seepage or sand boils.

“Given that scenario, any Illinois citizens who failed to follow evacuation orders issued on May 1 would have been in serious trouble, and the Cairo levee or seawall breach could have resulted in the loss of life as well as significant damage to city infrastructure and buildings,” he said.

When the levee was breached, flooding pressure on Cairo eased significantly and damage to the city was minimal. Flooding downstream, however, was significant.