The full flood control capacity of the Missouri River Mainstream Reservoir System is available for the 2021 runoff season. “All 2020 flood water stored in the annual flood control zone has been evacuated as of December 21,” says John Remus, chief of the Army Corps of Engineers’ Missouri River Water Management Division.
“The entire flood control capacity of the Mainstem System is available to capture and manage 2021 runoff, reducing flood risk while providing support to the other authorized project purposes.”
December 2020 runoff in the Missouri River Basin above Sioux City, Iowa, was 1.2-million-acre feet, 148 percent above average. The 2020 calendar year runoff above Sioux City was 31.1 MAF, 121 percent above average. The average annual runoff is 25.8-million-acre feet. The 2021 calendar year runoff forecast for the upper Missouri Basin above Sioux City is 23.1 MAF, 90 percent of the average runoff.
The runoff forecast is based on significantly drier-than-normal soil moisture conditions, low plains snowpack, and below-average mountain snowpack. “Runoff forecasts are developed using the best information as it exists today,” Remus adds. “As mountain snowpack continues to accumulate, our forecasts will be updated to reflect those changes.”