Corps inundated with snowmelt, spring rain: Garrison Dam held during crisis in 2011
GARRISON -- In 2011, the U.S. Army Corps of Engineers was hanging onto the Missouri River like an experienced horseman reining in a runaway horse. Through the spring and a long wet summer, the corps used every mechanism and feature it had to prev...
GARRISON -- In 2011, the U.S. Army Corps of Engineers was hanging onto the Missouri River like an experienced horseman reining in a runaway horse.
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 mighty river, the longest river in the country. If nothing else, the taxpayers of United States finally had to chance to see if they got their money’s worth.
The dam reservoirs filled to the brim with heavy mountain snowmelt and spring rain, but they held. For the first time, emergency spillway gates were opened 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, the situation could have been 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 even 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 five feet of water at that rate of flow, hard knowing where and how emergency dikes and levees would have held or failed.
It was really something to experience, according to Farhat, who said: “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 with the historic use of the spillway, normally a dry concrete expanse with 28 massive gates out of sight beneath the causeway. At the turn of a switch on June 1, the gates started creaking upward and water trickled then 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 reached near capacity in 1997, so he had no doubt the embankment would hold.
Looking back, Lindquist said that, as prepared as he and the staff tried to be, they were caught off-guard by the thousands 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 precedent for 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 pond day-use recreation facilities, until the force of the water finally blasted the narrow channel into a much wider opening as it remains today.
Lindquist said money intended to repair the spillway pond and swimming beach had to be diverted to the spillway gates that held strong but got beat up in the process. Work on the spillway gates is ongoing and, when done next year, 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 said.
Farhat said there were some important lessons from the event and the main one was for the corps to have a better handle on the amount of snowpack in the plains, as opposed to only the mountains, as well as the soil moisture going into freeze up.
“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.
Since the flood, the corps has spent $580 million on repairs to the dams and dam works and spent another $20 million during the flood event on temporary levees.
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 being in the position of opening the spillway gates when everyone knew the heartache that water would cause downstream was a very difficult one with no easy compromise between more, higher water faster, or slower less high water longer.
“I hope we never have to go through that again,” Lindquist said.