As dry conditions continue to reduce the flow of the Missouri River, the Corps of Engineers in September published the Draft Annual Operating Plan for the river for the 2021-22 season.
Drought conditions in the Missouri River above Sioux City, Iowa, are persisting. According to the U.S. Drought Monitor, the Missouri Basin shows at least Abnormally Dry conditions in 88% of the basin, with Extreme or Exceptional Drought present in 29% of the Basin, mostly in Montana and into the Dakotas.
Precipitation as a percent of normal for the July to September 2021 period was below normal for most of the basin except for central Wyoming, central and eastern South Dakota, and small areas of Nebraska, Iowa, Kansas and Missouri. Much of the basin experienced less than 70% of its normal precipitation accumulation over the latest 3-month period.
September runoff was 800,000 acre-feet, or 67% of average for the upper basin. Runoff was well below average in the upper three reaches of Fort Peck, Montana; Garrison, North Dakota; and Oahe, South Dakota; above average in the Fort Randall, South Dakota, and Gavins Point, Yankton, South Dakota, reaches, and slightly below average in the Sioux City reach.
The calendar year runoff forecast, updated Oct. 1, for the Missouri River Basin above Sioux City is 14.8 million acre-feet, or only 57% of average.
Support for the second half of the navigation flow support season—July 1 to Dec. 1—is 1,500 cubic feet per second less than a full-service level.
The system storage is 50.6 million acre-feet, well below the averages seen between 1967 and 2020.
Comment period
Seven public meetings to discuss the draft AOP are scheduled:
• Oct. 25 in Fort Peck, Montana, and Bismarck, North Dakota;
• Oct. 26 in Fort Pierre, South Dakota, and Sioux City, Iowa;
• Oct. 27 in Smithville, Missouri, and Nebraska City, Nebraska; and
• Oct. 28 in St. Louis, Missouri.
The meeting schedule is subject to change depending on COVID-19 protocols. Comments on this draft AOP must be provided by Nov. 24. The final AOP is scheduled for publication in December 2021.
The plan is not meant to be a forecast, the Corps notes; instead, it examines runoff scenarios encompassing 80% of the range of the historical record. “There is still a 10% chance that runoff will be higher than shown in the AOP and a 10% chance that it will be lower,” the DAOP notes.
David Murray can be reached at [email protected]
