(CNN)What happened in spring bodes ill for the summer.
March storms in the Midwest caused significant damage to the levee system of the Missouri River and now any strong or frequent rainfall this summer could trigger flooding along the lower Missouri River, experts say.
Kevin Low, service coordination hydrologist at the Missouri Basin River Forecast Center, a National Weather Service office, told CNN Friday that "it's been a very wet spring and it all started in March." During that month, more than 7 million people were under flood warnings because of the convergence of snowmelt, a "bomb cyclone" snowstorm and heavy rain in the heartland.
Since March, Low said, "it really hasn't stopped raining. We've kind of moved on from snowmelt to rain events one after the other."
Damage to the levees
Meanwhile, the March storm sent so much water into some of the Missouri River tributaries in such a short time that the water severely damaged the levee system, according to Eileen Williamson, deputy director of public affairs for the US Army Corps of Engineers. Some of the levees were "severely compromised, others breached," she said -- and now Missouri is probably most vulnerable to flooding because river waters remain higher there.
Dan Armstrong, a supervisory hydrologic technician with the US Geological Survey's Central Midwest Water Science Center, said the current situation is unusual if similar in some ways to the 2011 Midwestern floods, "but in some locations the river levels are even higher" because of significant and frequent rainfall this past spring.
He said he believes the lower Missouri River region, which "covers the area from downstream of Yankton, South Dakota, on down to St. Charles, Missouri, and on to the Mississippi River, is most vulnerable to flooding this summer.
"At least thousands of residents could be affected," he said, adding that people in that vicinity should "pay close attention to weather forecasts and National Weather Service flood warning through the end of the summer."
Low said no one knows when or where there will be flooding because it all depends on where the thunderstorms "set up." Still, the climate prediction center of the National Weather Service for the Missouri River Basin said chances are there will be "above normal" precipitation for the next three months, explained Low:
"It looks to be a very active season for the entire Missouri River basin," he said. "That doesn't bode well."
Longest river in North America
Nicknamed "Big Muddy," the Missouri River is the longest river in North America. It begins in the Rocky Mountains of western Montana and flows east and south for more than 2,300 miles before it enters the Mississippi River north of St. Louis. Its basin is in 10 states -- Colorado, Iowa, Kansas, Minnesota, Missouri, Montana, Nebraska, North Dakota, South Dakota and Wyoming.
The river's "basin" is all of the land surface that is dissected and drained by a river as well as all the streams and creeks feeding it.
A total of 218 flood or flash flood events happened in Missouri between March 1, 2018, and March 31, 2019, the most recent statistical date, according to the National Oceanic and Atmospheric Administration. One recent flash flood in Jefferson City, Missouri, submerged US Highways 61/67 following several rounds of heavy rain fall in September, according to the federal agency.
Today, Army Engineers are "everywhere" working to evaluate, assess and begin the repair process to the levees, Williamson said.
Repairing the levees involves "not just piling up dirt. It is an engineered and designed earthen embankment" that is built to keep a river from overflowing its banks, she said. If water rushes into a river too quickly, "it can knock the levee out -- and then it starts eroding the riverbank," she said. That poses a danger to the people who live near the river.
Low said people need to be "weather-aware" this summer by paying attention to local weather reports and getting information from his office at water.weather.gov. Any rainfall should be taken seriously by those who live in the Missouri River basin, he said.
"If you live or recreate near a body of water, you should look for information over the next couple of days before you enter the area," he said. "If you encounter a flooded roadway, don't try to cross it -- it's not worth the risk."
"Turn around, don't drown."