OMAHA — Several hundred thousand acres of rich Midwestern farmland and even some urban areas near the Missouri River are at risk of flooding this summer during months of historically high water that experts fear will overwhelm some levees, especially older ones.
Engineers who have studied past floods say the earthen levees in rural areas are at greater risk.
“Most of the levees are agricultural levees. They’re not engineered. They’re just dirt piled up,” said David Rogers, an engineering professor at Missouri University of Science and Technology.
Most levees have held along the 811 miles that the Missouri travels from the last dam at Gavins Point in South Dakota to its confluence with the Mississippi River near St. Louis.
So far, flooding has covered more than 560,000 acres of mostly rural land, including nearly 447,000 acres of farmland. The water has forced some evacuations, but the extent of the damage might not be clear until it recedes.
That is not expected to happen until the fall, as the Army Corps of Engineers said it needs to continue releasing substantial amounts of water from upstream reservoirs inundated with heavy spring rains and melt from an above-average Rocky Mountain snowpack.
The corps predicts that the river will eventually rise high enough to flow over about 18 to 70 levees, mostly in rural areas of southeastern Nebraska, southwestern Iowa and Missouri. Other levees will become saturated, and water can erode their foundations, seep underneath or find other flaws to exploit.
A saturated levee might lose stability, potentially causing it to crumble, as one did in June near Hamburg, Iowa, allowing floodwaters to cover several miles of farmland and threaten the town. Flaws in levees, such as animal burrows, can allow water to flow through and eventually destroy the structure.
“This is when we find out where the weak spots are,” said Erik Loehr, an associate professor of engineering at the University of Missouri.
Rural levees, experts say, are likely to be older, privately maintained and not tall or strong enough to stand up to such a long-running flood.
Corps officials and engineering experts are more confident that cities are well-protected by substantial floodwalls that have been maintained.
Jud Kneuvean, the emergency management chief for the corps’ district in Kansas City, Mo., said he feels good overall about the flood protection along the Missouri River, especially in downriver stretches.
“I believe here in the lower Missouri, we have some of the best levees in the nation,” Kneuvean said.
Numbers
560,000 acres Area flooded so far this year, mostly in rural areas
18 to 70 Number of levees the Army Corps of Engineers predicts the Missouri River will flow over, mostly in rural areas of southeastern Nebraska, southwestern Iowa and Missouri
