By Tim Webber, Des Moines Register
Residents along Iowa’s eastern border are once again dealing with a Mississippi River that doesn’t seem to want to stay in its lane, as melting snow and recent heavy rainfall have combined to create the conditions necessary for major flooding.
According to the National Weather Service, the worst of the flooding — the river’s crest — is forecast to occur over the weekend and into early next week, depending on the location along the river.
In far northeastern Iowa, that crest has already occurred, and the flooding will begin to subside over the next several days. Farther south, the river won’t reach its highest point until Tuesday or Wednesday.
As of Friday’s forecast, the river isn’t expected to reach any all-time records over the next week, but in some areas it could reach its third- or fourth-highest crest in recorded history.
Here’s how this week’s flooding is expected to compare to previous floods.
Mississippi River may exceed 1993 and 2008 heights in some locations
The Register identified four years of particularly bad flooding along the Mississippi over the past 30 years to compare with this year: 1993, 2001, 2008 and 2019.
Those floods affected different areas of the Mississippi. The 2001 flood caused the river to reach its highest levels since 1965 in Dubuque; 1993’s set an all-time record in Muscatine and 2008’s did the same in Burlington.
This year’s flood will cause higher crests, relative to previous historical floods, farther north. Between McGregor and Camanche, Iowa, the river is forecast to reach its third-highest levels ever, behind only 1965 and 2001.
With the exception of 2001, this week’s flooding is expected to exceed the floods of each of the four aforementioned years at least somewhere along the Mississippi River in Iowa.
If those years are the benchmarks for recent flooding in Iowa, 2023 could very well fit right in among them.
Where will flooding be worst in Iowa?
Nearly all of the National Weather Service’s flood gauges along Iowa’s portion of the Mississippi River are forecast to reach “major flooding” status — more on what that means below.
There are a few exceptions: At the gauges in Lansing, Iowa, and Lynxville, Wisconsin, the river has already crested with only moderate flooding. In Keokuk, the river is forecast to crest at just over 18 feet next Tuesday. That would also be considered “moderate” flooding.
Everywhere else along the Iowa-Illinois border, the flooding will be more severe, including several major cities along the border. Dubuque has closed all of its floodgates for only the third time ever. In Davenport, some roads have already been closed for several days.
What’s the difference between moderate and major flooding?
The National Weather Service uses a handful of terms to define how severe flooding could get. It can vary from location to location; it depends less on the river’s level relative to its banks and more on the river’s threat to the public.
Flood stage itself is the level where rising water levels can become hazardous to people or property. Within flood stage, the weather service defines a flood as “minor,” “moderate” or “major.”
Minor flooding is “inconvenience or nuisance flooding,” spilling into yards but not yet flooding buildings. Moderate flooding causes some roads and buildings near the river to be flooded, potentially causing evacuations. Major flooding is more extensive, shutting down roads and leading to significant evacuations.
The National Weather Service issues flood warnings when it expects moderate and major flooding — and it has done so all along the Mississippi River in Iowa this week.
Tim Webber is a data visualization specialist for the Register. Reach him at [email protected], 515-284-8532, and on Twitter at @HelloTimWebber.