Mandan Flood

March 21, 2023 — Ice blocking the Heart River near Mandan caused extensive flooding to the area on this day in 1948. The flooding eventually overtook the southern half of the city and cut-off transportation between Bismarck and Mandan. Although the flooding was due primarily to the buildup and breaking of ice floes on the river, the majority of the damage was confined to the lowland area at which the river flowed into the Missouri.

On the evening of March 20, dozens of volunteers began adding sandbags to the dikes surrounding the city as the river began to show signs of possible flooding. A haphazard dike was also thrown up across a threatened US Highway 10, the main thoroughfare connecting the city with the state’s capital.

Later that night, five families were forced to evacuate their homes, as the waters continued to rise. As residents of Mandan prepared for bed that night, the river flowed only two to three feet below the city’s emergency dikes. City officials warned that the water was likely to pour over the top of the dikes by morning. The Mandan Memorial building was opened up to house evacuees.

Overnight, a giant ice jam had formed upriver, causing the flood waters to slowly recede, but only delaying the disaster that was to hit the city. The residents of Mandan were forced to wait and watch the giant blocks of ice. Movements of the jam were tracked aerially by five planes posted above the city. Finally, on March 23, the ice gave way and flood waters rushed over the dikes. The hundreds of volunteers, drawn from local high schools and area businessmen, were forced to give up and watch helplessly as water engulfed the entire southern half of the city.

Hundreds were evacuated, and the army sent an amphibious duck loaded with blankets and cots to the city from Bismarck. Unfortunately, the icy waters were too much for the seven-ton vehicle, which was forced to turn back, and the aid had to be sent via railcar.

Icy chunks floating downriver stripped the bark off trees, snapped telephone poles, and even took out a steel bridge connecting the training school to the city. Spring flooding was not an uncommon occurrence for Mandan residents, however; the following year, construction on the Heart Butte Dam was completed in response to the river’s violent flooding episodes.

“Dakota Datebook” is a radio series from Prairie Public in partnership with the State Historical Society of North Dakota and with funding from Humanities North Dakota. See all the Dakota Datebooks at prairiepublic.org, subscribe to the “Dakota Datebook” podcast, or buy the Dakota Datebook book at shopprairiepublic.org.