A “tabletop exercise” became the pivotal step in preventing last year’s historic flood from being even more destructive than it was, a chief engineer for the U.S. Army Corps of Engineers said Wednesday.

“Every year, we’d drag out the Birds Point-New Madrid Floodway operation plan, look at it, then set it aside,” said Thomas L. Minyard, chief of engineering and construction for the Corps’ Memphis District, addressing the annual National Engineers Week luncheon at the BB Club. “We just didn’t think it was ever really going to happen.”

Last year during that exercise, for some reason, engineers blew out levees in southeast Missouri — on the tabletop — to inundate the Birds Point-New Madrid Floodway.

Then the real flood came.

The flood control point on the river’s west bank has been part of the system of floodways, spillways, locks, dams and other control structures comprising the Mississippi River & Tributaries Project since both were authorized by Congress in 1928, but has been activated only twice — January 1937 and May 2011.

The plan, which is to dynamite part of the mainline levee and allow the river to flood about 130,000 acres, is triggered when the gauge at Cairo, Ill., reaches 61.5 feet. The state of Missouri took the Corps to federal court to stop the action, but was unsuccessful.

The river reached 57.1 feet in Vicksburg, 14.1 feet above flood stage and nearly a foot above the 1927 mark. Levees north of Vicksburg, at Buck Chute and Lake Albemarle, are in the final stages of repair after sand boils cropped up before and during the water’s rise. Congress gave the Corps $802 million in December to fix levees up and down the river.

Minyard’s question to the estimated 125 people at Wednesday’s lunch asked what causes floods. His simple answer — rain — was measured between 600 percent and 1,000 percent above normal in the Ohio River Valley during the last two weeks of April last year and fell below control structures.

“When you get that much rain in that time period, it’s just too much and something has to give,” Minyard said.

A snowy winter of 2010-11 in the Midwest and Northeast has also been cited. Through Feb. 7, much of the upper Midwest had received up to 40 inches less than last year, according to the National Oceanic and Atmospheric Administration.

Activities this week to recognize engineers included the luncheon, put on by the Society of American Military Engineers, local branches of the Society of Women Engineers, American Society of Civil Engineers and Mississippi Engineering Society, and statewide sections of the American Society of Mechanical Engineers and the Institute of Electrical and Electronics Engineers.