OMAHA -- Runoff into the Missouri River above Sioux City may no longer be expected to reach record levels, but releases from the river's reservoirs will continue an at above-normal rate.
The U.S. Army Corps of Engineers has reduced the 2019 runoff forecast to 60.2 million acre-feet from 61 MAF, which would have tied 2011 as the highest runoff total in 121 years of record keeping. The annual average is 25.3 MAF.
Despite the lower total runoff forecast, runoff into the basin above Sioux City was above average in October, and the corps continues to evacuate the excess water that has flowed into the river's six reservoirs since March.
"Gavins Point (Dam) releases will remain near 80,000 cubic feet per second for the remainder of November to ensure flood control storage zones in all system reservoirs are emptied prior to the 2020 runoff season. This release rate is more than twice the average release for this time of the year," John Remus, chief of the U.S. Army Corps of Engineers' Missouri River Water Management Division in Omaha, said in a news release.
As of Friday, the amount of water stored in the Missouri River's six reservoirs was at 60.9 MAF, occupying 4.8 MAF of the 16.3 MAF of the system's flood storage capacity.
"Because of the high reservoir levels and the forecast for above-average runoff for the remainder of the fall, releases from all system projects will be much above average through November to evacuate all stored flood waters prior to the start of the 2020 runoff season," Remus said.
The Iacinos from left, Aaron Iacino, Tera Iacino, and their children, Samuel Iacino, 11, Isabella Iacino, 13, and Tatiana Iacino, 9, watch the high water at Chris Larsen Park in Sioux City, Iowa on Saturday, March 16, 2019. Sioux City Journal Photo by Justin Wan
Joe Stanek of Sioux City looks at the rising Missouri River with his sons, Anthony, left, and Joseph, at Chris Larsen Park in Sioux City, Iowa on Saturday, March 16, 2019. Sioux City Journal Photo by Justin Wan
Joey Shockman of Jefferson, 14, and his mother Arlene Shockman walk the dog as the Missouri River takes over part of the parking lot at the boat ramp at Chris Larsen Park in Sioux City, Iowa on Saturday, March 16, 2019. Sioux City Journal Photo by Justin Wan
High water at Big Sioux River is seen beneath Military Road Bridge at North Sioux City is shown Saturday. Flooding fears for communities along the Big Sioux eased Wednesday as the National Weather Service sharply lowered projected crests for the river.
Releases from Gavins Point near Yankton, South Dakota, will be reduced from 80,000 cfs to 22,000 cfs during December, reaching the winter release rate of at least 17,000 cfs by the middle of the month. Lower release rates are set during the winter because the river ices over in the northern reaches, limiting the amount of water that can flow beneath the ice.
Record-setting rainfall totals in many areas of Nebraska, the Dakotas and Montana this summer and fall have contributed to the near-record runoff, delaying the corps' ability to evacuate water throughout the year.
During a meeting in Sioux City last month, corps officials warned that soil is nearly saturated across much of the basin and can absorb very little new precipitation. If those conditions persist into the spring, runoff could again reach above-normal levels and lead to a greater risk of flooding.
Soils are expected to be near their moisture capacity when they freeze this winter, leaving little ability to soak up water once the ground thaws in the spring. Making matters worse: Forecasts suggesting a strong chance of precipitation late this fall.
Water flows through the spillways of Gavins Point Dam in Yankton, S.D., in April. The U.S. Army Corps of Engineers said Wednesday that releases will remain at more than twice the normal level through November to evacuate near-record runoff into the Missouri River reservoir system.