The U.S. Army Corps of Engineers is working to release a lot of stored floodwaters in the Upper Missouri River Basin to reduce the chances of flooding next spring.
The Corps said it has about two and a half months to get rid of more than 5 million acre-feet of water from flood control reservoirs. Just 1 acre-foot is equal to about 326,000 gallons. John Remus, Chief of the Missouri River Basin Water Management Division with the Corps said that is doable with the amount of water they’re releasing from Gavins Point Dam in South Dakota.
“Our runoff forecasts coupled with our reservoir studies say that if we maintain the 80,000 cubic feet per second out of Gavins Point Dam and the associated releases out of Fort Peck (Dam), Garrison (Dam) and Oahe (Dam), that we will reach that goal of 56.1 million acre-feet of storage by the next year’s runoff season," Remus said.
Runoff includes mountain snowpack, plain snowpack and rainfall. Remus said if there’s a lot more of this and the Corps can’t evacuate enough storage, that could increase flood risks for everyone from Bismarck, N.D. to St. Louis.
It’s been a wet year for the Missouri River Basin above Sioux City. The Corps is projecting 61 million acre-feet of runoff for the upper basin this year, which, if it’s reached, will tie with 2011 for the highest amount of runoff in a single year in the last 121 years. The Corps plans to bring Fort Peck, Garrison and Gavins Point Dam releases down after November, but will need to keep winter releases above average to evacuate the stored floodwaters.
Mike Gillispie, a service hydrologist with the National Weather Service in Sioux Falls, S.D., said there is still a lot of uncertainty about flooding next spring. But right now, soils are very wet and smaller lakes and ponds are all full. He compared the conditions to putting a wet sponge in a freezer.
“You’d start dumping water on top of that, all of that water is going to run off,” Gillispie said. “So we just don’t have that storage in the soils or in the ponds and lakes and streams and rivers, that we’re starting at such a high level it’s not going to take as much precipitation to start causing problems in the spring.”
Both Gillispie and Remus made their comments to Iowa Public Radio after a Corps public meeting in Sioux City, one of seven meetings the Corps holds twice a year from Fort Peck, Mont. to Jefferson City, Mo. to update the public about the year’s runoff and reservoir conditions.
During the Sioux City meeting, officials from the Corps told a large crowd about the projected record amount of runoff this year, what they’re doing to fix levees and manage flood control, and the conditions of the basin.
Corps of Engineers Reservoir Regulation Team Lead Kevin Grode said the six reservoirs on the river are storing 61.9 million acre-feet of floodwaters, and need to get down to 56.1 by the next runoff season. For the most part, he said, flood control storage belongs to the upper three reservoirs.
“We can get about a million acre-feet out during the winter time with above average winter releases,” Grode said, “So that means we need to get down to 57.1 by the end of November and we need to get down to winter releases by early December.”
“2019 has been a very, very wet year,” Grode added. “I’m sure you all have been experiencing that and know that.”
As for what to expect next winter, Gillispie with the National Weather Service told the public that for November through January, “We’re not saying warm and wet for the winter. We’re saying that the chances are higher and we’re weighting the dice a little bit … towards being warmer and wetter for that three-month period.”
Gillispie said it’s difficult to predict spring conditions this far in advance, but, “the odds are slightly higher right now that we are going to continue to see above normal precipitation at least through the first half, two-thirds of the winter.”
Starting in mid-February, the National Weather Service will release a 90-day outlook for the Missouri River based on its current and past conditions, Gillispie said. They’ll crunch a few scenarios so they can see what the river levels could look like this spring.
