Fort Peck Dam Runoff Lowest Ever Recorded
Drought conditions continue to impact the upper Missouri River Basin above Sioux City, IA. July runoff in the upper Basin was 34 percent of average. July runoff above Fort Peck Dam was the lowest in 123 years of record- keeping.
The updated 2021 upper Basin runoff forecast is 14.6 million acre-feet (MAF), 57 percent of average. If realized, this runoff amount would be the 10th driest year in the upper Basin since 1898. System storage on August 1 was 53.9 MAF, 2.2 MAF below the base of the Annual Flood Control and Multiple Use Zone. System storage is expected to decline further into the Carryover Multiple Use Zone during the remainder of 2021.
“Reservoir inflows in July have been declining due to the warmer and drier conditions in the upper Basin,” said John Remus, chief of the U.S. Army Corps of Engineers’ Missouri River Basin Water Management Division. “Per the July 1 System storage check, navigation support will be maintained at an intermediate service level, 1,500 cubic feet per second (cfs) below full-service levels, through the end of the normal 8-month navigation flow support season, which will end on Dec. 1 at the mouth,” added Remus.
USACE will evaluate lower Missouri River flow conditions to set Gavins Point releases to ensure that flows at the four downstream navigation target locations will be at or above the intermediate service level. The monthly study also indicates that the winter release from Gavins Point, which is based on the September 1 System storage check, will likely be at a minimum rate of 12,000 cfs Fall public meetings are currently scheduled to be held October 25-28 at several locations along the Missouri River. Locations and details will be included in the September update.
Soil conditions in the upper basin are very dry. Drought conditions throughout the entire Basin, particularly in the upper basin, worsened in July. According to the National Drought Mitigation Center, approximately 75 percent of the Missouri River basin is currently experiencing some form of abnormally dry or drought conditions, an increase of 10% since the end of June. The seasonal drought outlook, which extends through the end of September, shows drought conditions will persist or expand across the upper basin. Drought information can be viewed at droughtmonitor. unl.edu/.
Mountain snowpack in the upper Basin melted out in mid- to late-June, several weeks earlier than normal. The mountain snowpack peaked above Fort Peck in late March at 86% of average, while the mountain snowpack in the Fort Peck to Garrison reach peaked in late April at 96% of average. Mountain snowpack normally peaks near April 15. The mountain snowpack graphics can be viewed at go.usa.gov/ xARQC.
The winter release rate is determined based on the September 1 System storage. Per the July 1 reservoir studies, the winter releases from Gavins Point Dam will likely be at the minimum rate of 12,000 cfs.
Fort Peck Dam: Average releases past month – 9,400 cfs; current release rate – 9,500 cfs; forecast average release rate – 9,500 cfs; end-of-July reservoir level – 2230.8 feet (down 1.7 foot from July 1); forecast end-of-August reservoir level – 2228.8 feet. Releases will be maintained at 9,500 cfs through August.
