Friday, July 01, 2011

mighty missouri defies the corps


Video - Arnie Gundersen on Five O'clock Shadow with Robert Knight, WBAI, June 28, 2011 at 5:00 pm EDT

CapJournal | 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 25, Fort Peck reservoir is at 109.6 percent 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 passing through the reservoir and moving on downstream and the Army cannot stop it.

But that isn’t even the full story. The Rocky Mountain snowpack in Montana is now melting in earnest. In places, that snowpack had been at 140 percent of normal. That melt water (minus evaporation, seepage, and human withdrawals) is going to pass through Fort Peck reservoir. Then there is the issue of rainfall. The National Weather Service recently predicted above average precipitation across the northern plains for the next three months. The rains are going to come. As a matter of fact, portions of the Upper Missouri Basin may receive heavy, drenching rains in the next few days. If Montana receives additional monsoonal rains, that rainwater 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’s level stands at 1854.48 feet, which is equal to 103 percent of capacity. Garrison Dam can move 41,000 cfs through its five power tunnels and 98,000 cfs through its three flood tunnels (this figure is from the Omaha District’s website). Unfortunately, the dam’s tunnels have been unable to match the reservoir’s inflows. Consequently, the Missouri is now pushing 11,500 cfs through Garrison’s spillway. A second big dam athwart the Missouri can no longer stem the Great Flood.

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 1619.28 feet. Oahe can push a maximum of 167,000 cfs through its seven power tunnels and six flood tunnels. Oahe has only seven tenths of a foot of freeboard left before the Missouri laps against its spillway gates. The Army can increase discharges from Oahe from the present 150,300 cfs to 167,000 cfs to keep the river from the spillway — but doing so raises the flood threat to Fort Pierre and Pierre. Yet, to keep discharge levels at 150,300 cfs risks having the river enter the spillway and then discharge its uncontrolled waters downstream, where they will still inflict damage. If the Missouri goes into Oahe’s spillway, the river will have rendered it ineffective in halting 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 3.72 feet of freeboard in its reservoir (although on June 14th it had almost 12 feet of freeboard) 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. The Missouri will flow free and unchecked through the Army’s reservoirs and dam spillways. 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 its already tenuous hold on the Missouri. 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. Great quantities of melt water have yet to enter the system.

At this writing, thunderstorms are predicted for northeastern Nebraska, northwestern Iowa, and the Dakotas. The big question is whether the Army’s controlled flood, with its 160,000 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.

Robert Kelley Schneiders, Ph.D., environmental historian with Eco InTheKnow, LLC, P.O. Box 4393, Boulder, CO 80306, www.ecointheknow.com, author of “Unruly River: Two Centuries of Change Along the Missouri,” and “Big Sky Rivers: The Yellowstone and Upper Missouri.”

1 comments:

nanakwame said...

What is so ironic is the Great Sioux had created a system in this area to move up or down the Missouri River, they were amazed at Whites owning land and building around this great river.

"When the white man comes in my country, he leaves a trail of blood behind him." Red Cloud

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