Missouri River Dams Credited With Mitigating 2011 Floods

In 2011, the U.S. Army Corps of Engineers was hanging on to the Missouri River like an experienced horseman reining in a wild stallion.

Through the spring and a long wet summer, the corps used every mechanism and feature it had to prevent the Missouri River from causing the most severe flood in modern history. Garrison Dam and its upstream Montana sister, Fort Peck Dam, were built decades ago to control flooding on the longest river in the country. If nothing else, the U.S. taxpayers had the chance to see if they were getting their money’s worth.

The dam reservoirs filled to the brim with heavy mountain snowmelt and spring rain, but they held. Emergency spillway gates were opened for the first time for flood control, and they worked exactly as envisioned.

The river still ran too fast and too high to prevent downstream erosion and flooding; but without the dams, experts say, the situation could have become catastrophic rather than critical.

The dams allowed the corps to rein in the Missouri River flow to a peak flow of 150,000 cubic feet per second; unchecked, the river would have galloped toward Bismarck at the rate of 260,000 cfs, about 10 times the flow of a normal high-release rate.

Jody Farhat, chief of the corps’ Missouri Basin division, said at that rate the flood stage would have reached 24.2 feet at Bismarck, rather than 19.2 feet. With another 5 feet of water at that rate of flow, it’s hard to know where and how emergency dikes and levees might have failed.

It was really something to experience, according to Farhat. “It was just amazing to see the spillway, built so many years ago. We opened it in a crisis, and it operated as it was designed.”

Even as the corps worked with state and local officials to help understand and mitigate the high water heading south, it had its hands full at the dam works.

Turned out, people were absolutely fascinated by the historic use of the spillway, normally a dry concrete expanse with 28 massive gates out of sight beneath the causeway. Thousands gathered to watch June 1 as the gates started creaking upward and water roared down the structure, out into a spillway pond, through a 2-mile pilot channel and into the Missouri River.

Todd Lindquist, Garrison Dam’s project manager, remembers that time as a series of 18-hour days, coordinating emergency levee works in Bismarck-Mandan with one hand and managing emergency dam operations with the other.

“I do remember telling my wife there had to be easier ways to make a living. It was very stressful,” said Lindquist, pointing out that Garrison Dam also neared capacity in 1997, so he had no doubt the embankment would hold.

As prepared as he and the staff tried to be, he said, they were caught off-guard by the sheer number of onlookers who came to observe the historic flood release.

To control the flood of people arriving at the dam from all corners of the region and the state, the corps contracted with the McLean County Sheriff’s Department to set up parking and crosswalks.

The corps closed all of its downstream camping and boat ramp facilities during the release, partly because there was no way of knowing where the water would go.

Turned out, the pilot channel was too narrow and water backed up into the catchment pond and pushed west, damaging the popular day-use recreation facilities. The force of the water blasted the narrow channel into the much wider opening it is today.

Lindquist said money intended to repair the spillway pond and swimming beach had to be diverted to the spillway gates, which held strong but got beaten up in the process. Work on the spillway gates continues. When it’s done next year, it will have taken every summer construction season since the flood.

“The swimming beach is the feature that we regret losing the most. We hope to restore that day use at some point,” he told The Bismarck Tribune.

Farhat said the main lesson learned from the event was that the corps needs to have a better handle on the amount of snowpack in the plains, not just in the mountains, as well as the soil moisture level prior to the freeze.

“The state was collecting that information that we were not aware of. We now have much better systems in place, and are coordinating more on runoff forecasts,” she said.

The corps spent $20 million on temporary levees during the flood event. Since then, the corps has spent $580 million on repairs to the dams and dam works.

The Missouri River wasn’t the only one in trouble in 2011. Every river basin in North Dakota was impacted, and 21 peak records were set. It’s estimated the public cost for the 2011 flood fight and mitigation exceeded $1.4 billion, according to a Department of Emergency Services report from November that year.

Lindquist said it was difficult being in the position of opening the spillway gates when everyone knew the heartache that water would cause downstream; but there was no easy compromise between creating a flow of faster, higher water that would last a short time, and allowing a slower, lower level of water that would last longer.

“I hope we never have to go through that again,” he said.