Higher-than-average releases from all Missouri River Mainstem System projects, including Gavins Point Dam, will continue through November, the U.S. Army Corps of Engineers announced Wednesday.
“Gavins Point releases will remain near 80,000 cubic feet per second (cfs) 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,” said John Remus chief of the Corps’ Missouri River Basin Water Management Division.
Runoff in all reaches except for the Fort Randall reach was above average for the month of October. The Garrison to Oahe reach runoff was over six times the long-term average and runoff in the Gavins Point to Sioux City reach was more than 10 times the long-term average. The 2019 upper basin runoff forecast was lowered slightly to 60.2 million acre-feet. If realized, this runoff total would be 0.8 MAF less than 2011 (61.0 MAF), which is the highest runoff in 121 years of record-keeping. The January-October observed runoff (56.7 MAF) has already exceeded the second highest runoff, 49.0 MAF observed in 1997, with two months still remaining.
The Missouri River Mainstem Reservoir System total storage was 60.9 MAF as of Nov. 1, occupying 4.8 MAF of the 16.3 MAF flood control zone.
“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. We are monitoring the situation very closely and will make any necessary adjustments. Failure to evacuate the stored flood water will lead to increased flood risk in 2020,” said Remus.
Based on the Sept. 1 System storage, winter releases from Gavins Point Dam will be at least 17,000 cfs. Based on the latest reservoir studies, Gavins Point Dam releases will be reduced from 80,000 cfs to 22,000 cfs during December, reaching the winter release rate by the middle of December. Navigation flow support at the mouth of the Missouri River will end on Dec. 11.
Lower release rates must be set during winter months because the Missouri River ices over in the northern reaches limiting the amount of water that can flow beneath the ice.
The Corps will continue to monitor basin and river conditions and will adjust System regulation based on the most up-to-date information.
The comment period for the 2019-2020 Annual Operating Plan ends Nov. 22. The final AOP, which is to be completed in late December, will be posted on the Water Management website: https://www.nwd.usace.army.mil/MRWM/Reports/.
Updates on basin conditions, reservoir levels and other topics of interest can be viewed here: https://www.nwd.usace.army.mil/MRWM/MRWMApp/.