Missouri Valley Flood 2011: Potential for the Army to Lose Control

In the nearly two-centuries-long interaction between the Missouri and the United States Army Corps of Engineers, the river has repeatedly defied the Army’s attempts at control.  Today, the Army faces its greatest challenge to its regulation of the Mighty Mo.

As of June 8, 2011, Fort Peck reservoir is at 106% of capacity.  The lake is so full that water is now flowing through the dam’s emergency spillway.  Because the Army does not have the ability to halt the flows through the spillway without threatening the structural integrity of the dam, the dam and reservoir have lost the ability to curtail the Missouri.  For all intents and purposes, the Missouri has defeated Fort Peck Dam.  Water is just passing through the reservoir and moving on downstream.

But that isn’t even the full story.  The Rocky Mountain snowpack in Montana is only now beginning to melt.  In places, that snowpack is at 140% of normal.  All of that meltwater is just going to pass through Fort Peck reservoir.  Then there is the issue of rainfall.  June is the wettest month of the year on the northern plains and within Montana.  The rains are going to come.  The National Weather Service has predicted above-average rainfall for June in Montana this year because of the presence of La Nina in the Pacific.  As a matter of fact, Montana may receive 2 to 3 inches of rain in the next few days.  All of that water is going to pass through Fort Peck reservoir.

The next bulwark against the Missouri is Garrison Dam, situated 70 miles north of Bismarck.  Garrison is a colossus.  The dam rises 210 feet above the riverbed and stretches a little over two miles long from valley wall to valley wall.  Lake Sakakawea possesses an elevation of 1854 feet above sea level when at full capacity.  Today, the reservoir level stands at 1853.38 feet.  The Missouri is only inches away from entering the dam’s spillway.  With all the water currently moving through the unregulated Yellowstone (53,300 cfs at Sidney, Montana, today) and the now moot Fort Peck reservoir (a 101,000 cfs inflow in Fort Peck’s reservoir today), and the water still to come, the Missouri will surely enter Garrison’s spillway.  Once in the spillway, the Missouri will have defeated the regulatory ability of the second of the Army’s large dams.

Below Garrison, the Army built Oahe Dam.  It is one of the world’s largest structures.  At full capacity, Oahe’s reservoir has an elevation of 1620 feet above sea level.  At present, the reservoir is at 1619.12 feet.  Like Garrison, Oahe only has a few inches of freeboard left before the Missouri enters its spillway.  If that happens, the Missouri will have rendered it ineffective in stemming the river’s greatest deluge.  Big Bend Dam near Chamberlain has already had water through its spillway.  It cannot stop the Missouri.  Fort Randall is the last major Army bastion against the Missouri.  There is still over fifteen feet of freeboard in its reservoir before the Missouri enters its spillway.  If the river goes through its spillway, the lower valley from Yankton south will have no protection whatsoever from the river.  Gavin’s Point Dam does not have the reservoir capacity to absorb floodwaters emanating out from Fort Randall – it has to immediately release those high flows.

The Army is on the cusp of losing the river.  Its military officers and civilian engineers and hydrologists know it.  It is why they are feverishly attempting to drain the Dakota reservoirs as quickly as possible.  The problem is that they may be too late.  It is already June and the biggest surge of meltwater has yet to enter the system.  At this writing, thunderstorms are brewing in the atmosphere over Montana.  The big question is whether the Army’s controlled flood, with its 150,000 cfs out of Gavin’s Point Dam, will be sufficient to drain the reservoirs fast enough and open up additional storage capacity.  If it does, the Army will regain a semblance of control along the river.  If those releases are not enough, and the river goes into the emergency spillways of every upstream dam, the lower river will face an uncontrolled flood that may surpass anything in living memory.  Valley residents can only hope that the Army’s dominoes hold back the Missouri.

Author’s Note: If you use the ideas and/or statements in this article, please cite the source as Robert Kelley Schneiders, Ph.D., Eco InTheKnow, LLC, and provide a link to www.ecointheknow.com

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