Missouri River Flood of 2011: The Greatest Flood Since 1952

The coming flood along the Missouri will be the largest flood to strike the Missouri Valley since 1952.

In April 1952, the Missouri flooded a string of cities from North Dakota to the state of Missouri, including Bismarck, Pierre, Fort Thompson, South Sioux City, and Sioux City.  But since most buildings and roadways in 1952 existed outside of the river’s traditional floodplain, the monetary costs of the flood remained relatively low.

Nonetheless, the agricultural sector took a particularly hard hit during the flood of 1952.  The losses suffered by farmers came in many forms.  Floodwaters washed-out farm roads, destroyed agricultural equipment, filled rural homes with several feet of foul-smelling Missouri River silt, and prevented farmers from planting a crop that year.  The 1952 flood caused an estimated 179 million dollars in damages along the entire Missouri Valley from the Dakotas to the river’s mouth.  Western Iowa alone sustained 43 million dollars in damages.

Yet, the damage estimate did not include the destruction inflicted upon the Army’s navigation channel.  In 1952, the Missouri likely washed away millions of dollars worth of Army pile dikes and revetments.  And although the Army never provided a cost estimate of the losses inflicted on the navigation channel, it did admit that the Missouri had broken out of its confined channel, especially in western Iowa.   Following the flood, the Army acknowledged that in the reach between Sioux City and Omaha, “Much of the river has reverted to its original wild state, and bank erosion is severe at many locations.”  This statement was an admission that the Missouri had escaped from the Army’s wooden and rock cage and had begun to flow again through its natural floodplain.

The Great Flood of 2011 will not match the 1952 flood in water volume.  At the height of that earlier flood, the Omaha gauging station recorded a river discharge rate of 396,000 cubic feet per second.  By mid-June, The Great Flood of 2011 will carry between 150,000 and 200,000 cubic feet per second past Sioux City.  This figure is derived from combining the Army’s estimated 150,000 cubic feet per second discharge rate at Gavin’s Point Dam with the discharge rates of the uncontrolled James and Big Sioux rivers.

Although lacking the discharge rate of the 1952 flood, this year’s flood will likely far surpass that earlier flood in the cost of damages.  The reason is simple – there is far more development in the Missouri Valley today than in 1952.

According to the Army’s own inundation projections, floodwaters of up to ten feet in depth will sink homes in Dakota Dunes, South Dakota, multi-million dollar facilities at the waterfront at Sioux City and South Sioux City, residential and commercial segments in South Sioux City, industrial areas south of Sioux City, low-lying sections of Interstate 29, and vast stretches of agricultural land in the lower valley.  For example, the Army has concluded that the Missouri will extend almost ten miles across its valley floor west of Missouri Valley, Iowa.  The Army is also warning valley residents that floodwaters may remain atop the valley floor for up to two months.  If that occurs, agricultural production in one of the world’s most fertile valleys will be significantly curtailed this summer.  But the damages will not stop there.  The navigation channel will be pounded by the flooding Missouri.  The river will erode, undermine, and outflank the Army’s pile dikes and revetments.  Along some reaches, the Mighty Mo might even break out of its navigation channel; and, as in 1952, it may revert to its original wild state.

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