The 2011 flooding event on the Missouri River in the United States was triggered by record snowfall in 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; Saint Joseph, Missouri; Kansas City, Missouri; Jefferson City, Missouri, and St. Louis, Missouri.Missouri River Near Williston, North Dakota - National Weather Service Many smaller towns were also at risk, suffering the same fate as the larger cities if not worse. 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.
Background
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 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 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.
In attempting to control the flood water release in since all the reservoirs were 100 percent or more of capacity (with the exception of the Fort Randall Dam), the Corps of Engineers doubled the record release of water in the river's five North and South Dakota dams. Officials said that problems downstream could have been alleviated by river control work and new levee construction that came about in the wake of the Great Flood of 1993. However, they were unsure whether the levees could sustain being waterlogged in a long-term flood.
A study by Utah State University examined the buildup of water storage leading to the 2011 Missouri River flooding observed by GRACE satellites indicated that precipitation over the MRB undergoes a profound modulation during the transition points of the Pacific quasi-decadal oscillation and associated teleconnections. The results infer a prominent teleconnection forcing in driving the wet/dry spells in the MRB, and this connection implies persistence of dry conditions for the next 2 to 3 years, which is linked to the 2012–2013 Midwestern drought.
Release of water by dam
In May 2011, dams above Gavins Point began stepping up the release of water (in cubic feet/second), exceeding all previous nationwide records for release. DamPrevious record flowPrevious record yearFlow May 1, 2011Flow May 31, 2011Flow June/July 2011 Fort Peck Dam35,00019757,0009,70065,500 (June 19) Garrison Dam65,000197517,40080,400150,200 Oahe Dam59,000199729,40086,300160,300 Big Bend Dam74,000199721,20083,900165,000 (planned) Fort Randall Dam67,000199742,30076,600157,000 (planned) Gavins Point Dam70,000199745,00077,000160,700
Missouri River bridge closings
The flood forced the closing of several Missouri River traffic bridges from just above Gavins Point to northern Missouri. The closings made it impossible to cross the river for more than between Sioux City and Omaha and another between Plattsmouth, Nebraska (just south of Omaha) at Mile Marker 591 and St. Joseph, Missouri, at Mile Marker 450. Authorities were also considering closing the Plattsmouth Bridge.
During the flood, every bridge between Omaha and Kansas City was either closed entirely, had exit ramps blocked or had other work at some point.
Long term closings Chief Standing Bear Memorial Bridge between Nebraska and South Dakota near Niobrara, Nebraska. The bridge actually remained open but flooding on the Nebraska side made it a dead end. However, some people (particularly employees at the Mike Durfee State Prison) used motor boats, kayaks, chest waders, and a homemade “swamp bike” to commute between the bridge and their cars outside the flood area. Burt County Missouri River Bridge (Mile 691) between Nebraska and Iowa near Decatur, Nebraska Mormon Bridge (Mile 622) between Nebraska and Iowa north of Omaha, Nebraska (Interstate 680) Bob Kerrey Pedestrian Bridge (Mile 616) – the pedestrian bridge between downtown Omaha and Council Bluffs which had been a popular viewing spot of the flood but was closed temporarily on June 30 while river debris was cleared from its base. The Council Bluffs side was closed on July 2 due to flooding on that side. It reopened September 3. Nebraska City Bridge (Mile 561) between Nebraska and Iowa (near Nebraska City, Nebraska) Brownville Bridge (Mile 535) between Nebraska and Missouri at Brownville, Nebraska Rulo Bridge (Mile 497) between Nebraska and Missouri at Rulo, Nebraska Amelia Earhart Bridge (Mile 422) between Kansas and Missouri at Atchison, Kansas. The bridge was open between Atchison and the small unincorporated community of Winthrop, Missouri, immediately across the bridge; however, access to Kansas City or St. Joseph on the Missouri side via U.S. Highway 59 was closed. Residents of Winthrop were evacuated on June 27.
Short-term closings/interruptions Blair Bridge (U.S. Route 30) (Mile 648) — The bridge closed from June 27-July 1 while flood barriers were erected in Iowa. It was also closed again July 6–7 for further shoring up work. Bellevue Bridge (Mile 602) – The bridge was closed June 27-July 2 due to flooding and sandbagging of Iowa Highway 370. Flooding in Haworth Park at the base of the bridge in Bellevue, Nebraska, had water up to the top of its basketball hoops on July 2. Pony Express Bridge (Mile 448) – Southbound exit in Elwood, Kansas, was closed temporarily on June 28 while storm water could be pumped off Centennial Bridge (Leavenworth, Kansas) (Mile 396)- Scheduled resurfacing work on the bridge had started in May prior to the flood, and traffic had been reduced to one lane. Since it was one of the few bridges open for traffic between Omaha and Kansas City, work on the bridge was halted indefinitely on July 1
Flood stages and effects by state
Montana
On May 22, 2011, flooding of the Little Bighorn River and nearby tributaries inundated Crow Agency and shut down Interstate 90 between Hardin and the Wyoming state line. May 26 flooding on Musselshell River inundated portions of Roundup. Waters from the Shields River entering the Yellowstone River created flooding that closed a portion of Interstate 90 from Livingston to Springdale. Flooding on Pryor Creek, another tributary of the Yellowstone River prompted closing of Pompeys Pillar National Monument.
North Dakota
On May 10 President Barack Obama declared much of North Dakota a disaster area over flooding which began on February 14 and had been continuing.James River near Grace City, North Dakota - National Weather Service
Some of the most dramatic flooding in North Dakota was on Souris River which comes close to the Missouri but is not a tributary as it flows instead north into the Assiniboine River in Canada, which also experienced prior flooding. 10,000 people in Minot were evacuated on June 1. On June 20 after they returned, officials announced that a new crest from new heavy rains would result in the river being a foot higher than the first crest. On June 21, 12,000 people, a quarter of the town's population, were ordered to evacuate after Lake Darling Dam had to step up its release of water. Amtrak suspended service on the Empire Builder through Minnesota, North Dakota and eastern Montana.
South Dakota
On June 1, nearly 3,000 people in Pierre and Fort Pierre were evacuated.
On June 3, South Dakota governor Dennis Daugaard urged residents in the Country Club section of Dakota Dunes (which is below Gavins Point Dam) to evacuate. He noted that it might be two months before they could return.
On June 21, South Dakota reported its first flood fatalities when two women drowned in Lyman County, South Dakota, after they drove their car down a washed out road. The fatalities were unrelated to flooding and increased releases on the Missouri River, but rather related to flash flooding from heavy rains according to the Lyman County Herald of Presho, S.D.
On the same day Pierre, South Dakota, officials estimated costs from the flood would be $13.2 million for that community.
On June 30, the spillway at Big Bend Dam was temporarily closed for inspections.
Iowa On June 10, the WinnaVegas Casino, which is owned by the Winnebago Tribe of Nebraska, near Sloan, was inaccessible. Shortly after, a yellow amphibious vehicle known locally as "the Duck" was used to provide transportation from Sloan across the floodwaters to the casino. The Duck now makes annual appearances as a float in Winnebago High School's homecoming parade.
On June 4, near River Mile 575 (near Hamburg), the main levee suffered a partial collapse. One June 5, it suffered a second partial collapse. On June 7, it suffered a third partial collapse. Finally, on June 13, it suffered a total collapse and had a wide gap. After the first partial collapse, the Corps of Engineers initiated an emergency contract to raise the levee immediately surrounding the town in order to protect it from an estimated of flood water.
On June 22, a mandatory evacuation of all residents in Mills County between Interstate 29 and the Missouri River was declared.
On June 25, a levee breach north of Council Bluffs flooded an area of Harrison County which could impact U.S. Route 30 connecting Blair, Nebraska and Missouri Valley, Iowa. DeSoto National Wildlife Refuge was also impacted by the break in the levee.
On June 27, officials said water "could begin slopping" over the emergency levee at Hamburg on its west side. The Nishnabotna River on its east side was reported to be two feet above flood stage.
On July 1, the main levee near Percival (16 miles north of Hamburg) breached in the early morning hours adding to the flooded conditions from the Hamburg breach. The breach occurred despite a month-long battle by the local residents.