Torrential rain caused catastrophic flooding in the Midwest

Today’s Image of the Day from NASA Earth Observatory features record-breaking water levels in the Big Sioux River which overtopped its banks on June 24, 2024. The false-color image highlights the presence of water, appearing dark blue. 

Torrential rainfall across the Midwest 

In late June, more than a foot of rain fell on parts of South Dakota and Iowa in the Midwest, causing rivers to overflow and resulting in significant destruction. The overflowing rivers demolished homes and bridges and inundated farmlands.

The areas of the Midwest that were hit hardest by excessive rain were south of Sioux Falls, South Dakota. 

“A front of dense moisture, drawn north from the Gulf of Mexico, parked over southeastern South Dakota and northwestern Iowa on June 20 and 21, unleashing torrential rainfall. Mitchell and Sioux Falls, South Dakota, recorded 6.5 and 7.7 inches of cumulative rain, respectively,” said NASA.

“It was the wettest two-day period for these cities in the National Weather Service’s (NWS) climate record, dating back to 1893. In Canton, South Dakota, near Iowa’s border, about 15 inches of rain fell on those days, according to NWS estimates.”

Saturated soils in the Great Plains 

The National Water Center noted that the front brought rain to already saturated soils, as the Great Plains region had received 150-200 percent of its normal rainfall from mid-May to mid-June. 

Using soil moisture data from NASA’s Short-term Prediction Research and Transition (SPoRT) center, the NWS forecasted that the ground could not absorb more water.

Big Sioux River 

The Big Sioux River, which borders Iowa and South Dakota, reached record heights following the consecutive days of heavy rainfall. 

On June 23, the river level in Sioux City, Iowa, rose to nearly 45 feet, 7 feet higher than the previous record. That evening, a steel railroad bridge connecting North Sioux City, South Dakota, with Sioux City, Iowa, collapsed into the Big Sioux River.

Rock Valley flooding

In northwestern Iowa, about a foot of rain fell over two days near Rock Valley, 50 miles southeast of Sioux Falls. 

The excessive rain brought the Rock River to an all-time high of 27 feet (major flooding stage is 19 feet). On the morning of June 22, the river broke a levee in Rock Valley, flooding the town and forcing 4,000 residents to evacuate. 

Blue Earth River 

Subsequently, the front moved over southern Minnesota, causing water levels to rise along several rivers in the state. Rising waters on the Blue Earth River washed out a portion of the Rapidan Dam near Mankato, according to news reports.

As of June 25, water levels of many rivers in the Great Plains had begun to fall but remained at major flooding stage, according to the NWS.

Image Credit: NASA Earth Observatory 

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