Reservoir inflows on Upper Missouri River Basin remain below average

Nebraska City News-Press

The reservoir inflows in the Missouri River basin above Sioux City, Iowa (Upper Basin) were well-below average in February.

The 2021 calendar year runoff forecast for the upper basin remains below average.

“Very cold February temperatures in the Upper Basin locked up tributaries in ice and reduced inflows to the system reservoirs,” said John Remus, chief of the U.S. Army Corps of Engineers’, Missouri River Basin Water Management Division.

“Mountain snowpack continues to accumulate in the Rocky Mountains; however, plains snowpack is well-below seasonal averages and soil moisture continues to be much drier than normal,” he said.

February 2021 runoff in the upper Basin was 0.8 million acre-feet, 70 percent of average.

The 2021 calendar year runoff forecast for the Upper Basin is 21.8 MAF, 84 percent of average. The runoff forecast is based on soil moisture conditions, plains snowpack, mountain snowpack, and long-term precipitation and temperature outlooks.

“Prior to the outbreak of cold, Arctic air, Gavins Point releases were increased to 19,000 cubic feet per second to lessen the impacts of ice formation on the lower Missouri River. The system hydropower plants increased energy production during the coldest days to compensate for the increased energy demands throughout the region,” added Remus.

System storage is currently 55.6 MAF, 0.5 MAF below the base of the annual flood control zone.

The system is positioned to serve all Congressionally authorized purposes during 2021, including flood control, navigation, and water supply. Navigation Beginning in mid-March, releases from Gavins Point Dam will be adjusted to provide flow support for Missouri River navigation.

Current studies indicate that flow support for Missouri River navigation will be at the full-service level for the first half of the 2021 season, which begins on April 1 at the mouth.

Full-service flow support is generally sufficient to provide a 9-foot-deep by 300-foot-wide channel. The actual service level will be based on the total volume of water stored in the system on March 15, in accordance with the guidelines in the Master Manual.

Flow support for the second half of the navigation season, as well as navigation season length, will be based on the actual July 1 system storage.

Full-service navigation flow support is expected at the dates and locations shown below. Sioux City: March 23 Omaha: March 25 Nebraska City: March 26 Kansas City: March 28 Mouth near St. Louis: April 1 Ice Conditions River ice conditions below all system projects, which have been closely monitored this winter season, will continue to be monitored through the spring ice break-up.

In early February, Gavins Point releases were increased to 19,000 cfs prior to the cold weather to lessen the impacts of ice formation on the lower Missouri River.

Releases were reduced to 17,000 cfs near the end of February.

Basin and river conditions continue to be monitored, including plains and mountain snow accumulation, and system regulation will be adjusted based on the most up-to-date information.

The river ice report is available at: http://go. usa.gov/xARQc. Mountain and Plains Snowpack Mountain snowpack in the upper Basin is accumulating at below-average rates.

The March 1 mountain snowpack in the Fort Peck and the Fort Peck to Garrison reaches was 94 percent of average.

By March 1, about 80 percent of the total mountain snowpack has typically accumulated. Mountain snowpack normally peaks near April 15.

The mountain snowpack graphics can be viewed at: http://go. usa.gov/xARQC.

Currently, plains snowpack in the upper Basin is light. Spring Public Meeting The spring public meeting will be held virtually on Tuesday, April 6 at 1 p.m. CDT by conference call and webinar.

The purpose of this meeting is to update the region on current hydrologic conditions and the planned operation of the mainstem reservoir system during the coming months.