2011 Missouri River floods
The 2011 Missouri River floods was a flooding event on the Missouri River in the United States. The flooding was triggered by record snowfall in the Rocky Mountains of Montana and Wyoming along with near-record spring rainfall in central and eastern Montana. All six major dams along the Missouri River released record amounts of water to prevent overflow which led to flooding threatening several towns and cities along the river from Montana to Missouri; in particular Bismarck, North Dakota; Pierre, South Dakota; Dakota Dunes, South Dakota; South Sioux City, Nebraska, Sioux City, Iowa; Omaha, Nebraska; Council Bluffs, Iowa; Kansas City, Missouri; Jefferson City, Missouri, as well as putting many smaller towns at risk. According to the National Weather Service, in the second half of the month of May 2011, almost a year's worth of rain fell over the upper Missouri River basin. Extremely heavy rainfall in conjunction with an estimated 212 percent of normal snowpack in the Rocky Mountains contributed to this flooding event.
The flood, rather than being a short term event, was anticipated to last from June through August 2011 as a result of attempts by the Corps of Engineers to regulate the release of water through 850 miles (1,370 km) of open river from Garrison Dam in North Dakota to the confluence with the Mississippi River at St. Louis. The Garrison Dam began releasing a record of 152,000 cubic feet (4,300 m3) of water per second on June 1, 2011—more than twice the previous record release in 1997. The Corps was criticized for not releasing the water earlier. However the Corps defended its practice noting that it did not foresee a cooler than normal spring which delayed the mountain snowmelt and the record sustained torrential spring rains in Wyoming and Montana.
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