YANKTON, SD (KTIV) – The Gavins Point Dam is the last line of defense along the Missouri River when it comes to flood protection. But how exactly does it work?
Anyone who lived here in 2011 remembers the historic flood on the Missouri River. At Gavins Point Dam, you can still see the water line around the concrete of the dam and powerhouse showing how high the river was that year. It hasn’t risen that high since, as the Missouri Flood of 2011 was one that went down in the record books.
But how did it happen?
During the winter of 2010-2011, much of the northern Rocky Mountains and Upper Plains received heavier-than-usual snowfall. In the spring, cooler temperatures kept the snowpack in place, followed by record-breaking rainfall in May and June in areas north of Siouxland. All of that moisture wreaked havoc downstream, creating one of the worst floods the Missouri River Basin has ever seen.
The river’s level rose rapidly in May after the U.S. Army Corps of Engineers increased discharges from dams upstream. The river flooded communities downstream. The spillway gates at Gavins Point, the last dam on the Missouri, were wide open, releasing 160,000 cubic feet of water per second.
To put that in perspective, “The normal average daily discharge at Gavin’s Point is 30,000 cubic feet per second,” said Michael “Moose” Welch, the U.S. Army Corps of Engineers’ operations project manager for the Gavins Point Project.
READ MORE: Gavins Point Dam: Its History and Creation on the Missouri River
Flooding continued throughout the summer and only receded when the Army Corps reduced flows in September.
Then came 2019 and another wave of flooding along the Missouri River Basin. January through May 2019 was one of the wettest times in the region. All of that water led to the 2019 Missouri River floods.
The floods occurred in the spring, when the ground was still frozen from the winter months, and the water flowed into the surrounding rivers and streams.
This year, Gavins Point and Lewis and Clark Lake were at capacity, with discharges reaching up to 90,000 cubic feet per second.
Flooded communities are looking to the U.S. Army Corps of Engineers and Gavins Point for the cause of the flooding. But it’s not that simple.
“Our reservoir control management is an equation that extends to the Mississippi River and takes into account the endangered species program, the Missouri River Restoration Master Plan, power generation, local weather, regional weather events, forecasted regional weather events. That’s all part of the equation and it’s not just one part and people lose context,” Welch explained. “It’s not just a decision at Gavins Point. It’s 22% of the United States and then the river to St. Louis and that’s all part of it. And it’s an equation for flowing water.”
Fort Randall, Big Bend, Oahe, Garrison, Fort Peck and Gavins Point are the 6 dams along the Missouri River. Each of them helps regulate and monitor the water levels of the Missouri River and dozens of tributaries in 9 states. It’s a big mathematical equation with many moving parts and factors to prevent flooding.
But Mother Nature also plays a role.
“We go through a planning scenario where we calculate the number of millions of acre-feet of storage capacity in all five reservoirs. And then they look at what’s forecast for next March or April, and the snowpack is coming out of Fort Pack and Garrison in April, May and even into early June,” Welch explained. “So those are all parts of this magic math equation.”
READ MORE: Gavins Point Dam: A look inside the powerhouse and spillway
When it comes to flooding and flood prevention, countless factors come into play. In 2011, the Missouri River was inches away from reaching the power plant’s doors. Could such a flood happen again?
I asked Welch.
“If it got higher, one of the questions I would ask is how do we seal that door,” Welch said as we stood on the power plant deck overlooking the Missouri River. “Will it ever happen again? I don’t know. But the other side of the question is: Could it happen? Yes, it could. Will it happen? I don’t know.”
For more photos of the 2011 flood, visit the National Park Service website.
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