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Saturday, May 28, 2011

Another "Great Flood": Missouri River

We've had what's been called the "Great Flood of 2011" in the Lower Ohio and Mississippi River Valleys. This may not be the only Great Flood of 2011, though.

Torrential rain, plus meltwater from the season's heavy snowfall has sent rivers well above flood stage in the Upper Missouri River Basin, from the northern Rockies into the Northern Plains.

You can see this in the maps below. At left, we show May precipitation anomalies. Note the darkest green shading in eastern Mont. highlighting where precipitation is most above average. In fact, Billings, Mont. has had its record wettest month, getting over half its average annual precipitation (rain, melted snow) in less than a month! Rain events of 1-3" are a big deal in this part of the nation!

In the map at right we show water values in the current snowpack compared to average for this time of year. All the purple squares denote snow water contents over twice the average for late May!

The combination of snowpack yet to melt and heavy spring rainfall has already lead to heavy flooding in numerous locations in Montana, in particular. As you can see from the map below, the Missouri River Basin drains east out of Montana into North Dakota, then southeast through the Dakotas, Nebraska, Iowa, then Kansas and Missouri.

So...similar to what happened along the Lower Mississippi River, what happens upstream becomes a problem downstream later.

In fact, the U.S. Army Corps of Engineers is anticipating flows from 5 of 6 dams along the Misssouri River to reach record levels to help mitigate the flooding as best as possible and keep reservoir levels from reaching the top of spillway gates. Unfortunately, this will mean flooding of parts of Bismarck, N.D., Pierre, S.D. and Sioux City, Ia., as the Missouri River will be raised to the 3-6' level above flood stage. This river flooding could last for months, in some locations, according to the Army Corps.

TWC YouTube Channel: Watch flooding video

The Missouri River Basin covers 10 states and 2 Canadian provinces
Image: USGS, DEMIS map server

Let's give you a rundown of the state-by-state impacts of this flooding, with news impacts courtesy of the Associated Press and National Weather Service:


A dike built in 1967 burst, sending up to 6 feet of water into parts of Roundup. Record flooding along the Musselshell River.
High water forced a closure of I-90 from Livingston to Springdale, Mont. Thursday and also from Hardin to the Wyoming border. They reopened Friday.
Dozens of roads closed, including 170-mile stretch of U.S. 12 from Harlowton to Forsyth.
Record flooding also earlier this week on the Musselshell River at Harlowton.
Emergencies have been declared in 51 Montana counties and Indian reservations.
Montana's rain swollen rivers and streams - 10 times their usual size in places - continued to carry a torrent of damaging debris through small towns and over roads Friday.

The Musselshell River floods the town of Roundup in this aerial view on Thursday, May 26, 2011. Several feet of water covered low lying areas along the river.
AP Photo/Billings Gazette, Larry Mayer

North Dakota

Missouri River is just a fraction of an inch away from record level at Williston, N.D. (set in April 1912)
Inflow into Lake Sakakawea estimated at 113,000 cubic ft./second Wednesday, an "astronomical amount", per the Army Corps.
Some residents of Bismarck told to prepare to evacuate, if necessary. Riverwood Drive closed for construction of a dike.
City of Fargo, N.D. provided City of Bismarck with a sandbagging machine capable of filling 10,000 bags in an hour. Moorhead, Minn. also providing 250,000 sandbags by truck.
Animals at Dakota Zoo evacuated Thursday to other zoos in the Dakotas.

Click for interactive map
Map of Missouri River in N.D. Bismarck is at lower-right. Garrison Dam denoted by orange locator dot.

South Dakota & Downstream

Gov. Dennis Daugaard warned of "imminent flooding" along the Missouri River in parts of Pierre and Ft. Pierre.
100-150 homes in Pierre and another 200 homes in Ft. Pierre may be affected by flood waters or underground water seeping through basement floors.
Elevated flood levels may persist into July!
Major flooding also continues along stretches of the James River, including near Huron, Ashton, and Stratford.
Releases at Gavins Point Dam near Yankton may top the 1997 record by early June, increasing through the end of June.
Army Corps: River stages 3-6 feet above flood stage are expected from just below Sioux City, Ia. to just north of St. Louis later this summer.
Water already encroaching on Ft. Calhoun, Neb. and Sloan, Ia.

Click for interactive map
Map of Missouri River near Pierre, S.D.

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