Forecast runoff for upper Missouri River basin lower after warm spring

Gavins Point releases are forecast to remain near 35,000 cubic feet per second through the month of April.

The upper Missouri River basin March runoff fell in line with the March 1 forecast. Runoff above Sioux City, Iowa was 5.5 million acre feet, which is almost two times average. The above average runoff was primarily due to plains snow melting over heavily saturated soils.

“The warmer-than-normal temperatures melted most of the plains snow in the eastern and central Dakotas. Along with the steady, but near average, rate of snow accumulation in the mountains, the projected upper Missouri River basin runoff for 2020 has been slightly reduced,” said John Remus, chief of the U.S. Army Corps of Engineers’ (Corps) Missouri River Basin Water Management Division.

Based on current soil moisture conditions, current plains and mountain snowpack, and long-term temperature and precipitation outlooks, the 2020 calendar year upper basin runoff forecast is now 35.5 MAF above Sioux City, Iowa. Although this forecast is a reduction of 1.4 MAF from the March 1 forecast, it is still in the top 10 percent of the 122 years of runoff record. Average annual runoff for the upper basin is 25.8 MAF. The runoff forecast is updated on a monthly basis, and more often if basin conditions warrant.

“This is still an above average runoff forecast and much of it depends on whether the mountain snow peaks in mid-April and if rain events or lack of rain differs significantly from what the climate outlooks indicate,” said Remus.

Soil moisture conditions continue to be very wet in much of the upper Missouri River Basin, which increases the potential for above average runoff in the upper basin. The potential for flooding remains, particularly in the lower river due to continued high river stages on many of the uncontrolled tributaries downstream of the Missouri River Mainstem Reservoir System.

When possible, additional adjustments to Gavins Point releases may be made to offset tributary flows from heavy rain events.

“Because System release adjustments may be more frequent, I encourage all interested parties to check the Missouri River Basin Water Management and the National Weather Service websites on a daily basis for the most up-to-date information on System conditions and forecasted river stages,” said Remus.

As of April 1, the total volume of water stored in the System was 58.5 MAF, up 2.2 MAF since March 1, occupying 2.4 MAF of the System’s 16.3-MAF flood control zone.

Navigation:

The March 15 system storage check indicated flow support for Missouri River navigation will be at least full service for the first half of the 2020 season, which began on April 1 at the mouth. Full-service flow support is generally sufficient to provide a 9-foot-deep by 300-foot-wide channel. Because of the higher runoff forecast the current service level is above full service 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.

Mountain Snowpack:

Mountain snowpack is slightly above average in both reaches. The mountain snowpack normally peaks near April 15. The mountain snowpack graphics can be viewed here: https://go.usa.gov/xE6wT.

Weekly updates on basin conditions, reservoir levels and other topics of interest can be viewed here: https://go.usa.gov/xE6wa.

Monthly Water Management Conference Calls

Water management calls include an update from the National Weather Service’s Missouri Basin River Forecast Center, an update on the Missouri River mainstem reservoir system operations, and updates on the ongoing and planned flood recovery efforts in both the Omaha and Kansas City districts. The next call for 2020 will be held Thursday, April 9, for Congressional delegations; Tribes; state, county and local government officials, levee and drainage districts; and the media. Calls will be recorded in their entirety and made available to the public on the Defense Video and Imagery Distribution System at www.dvidshub.net/unit/usace-nwd.

Spring Public Meetings:

The spring public meetings were canceled on March 23 to further reduce potential exposure to COVID-19.

A series of four videos providing the technical information concerning planned mainstem system operations will be made available on April 10 at https://go.usa.gov/xvbNR.

Moderated question and answer sessions with the public will be held via conference call April 20-23. These dates allow time following the videos’ release for viewers to submit questions in advance of the calls.

The videos and conference call details will be released on April 13.

Reservoir Forecasts:

• Gavins Point Dam
  • Average releases past month – 33,100 cfs
  • Current release rate – 35,000 cfs (as of April 1)
  • Forecast release rate – 35,000 cfs (average for April)
  • End-of-March reservoir level – 1206.8 feet
  • Forecast end-of-April reservoir level – 1206.0 feet
  • Notes: Releases will remain at 35,000 cfs in April, basin conditions permitting.
     
• Fort Randall Dam
  • Average releases past month – 25,100 cfs
  • End-of-March reservoir level – 1354.6 feet
  • Forecast end-of-April reservoir level – 1355.2 feet
  • Notes: Releases will be adjusted as necessary to maintain the desired reservoir elevation at Gavins Point.
     
• Big Bend Dam
  • Average releases past month – 31,700 cfs
  • Forecast average release rate – 27,200 cfs
  • Forecast reservoir level – 1420.0 feet
     
• Oahe Dam
  • Average releases past month – 30,400 cfs
  • Forecast average release rate – 22,100 cfs
  • End-of-March reservoir level – 1609.8 feet
  • Forecast end-of-April reservoir level – 1612.2 feet
     
• Garrison Dam
  • Average releases past month – 23,200 cfs
  • Current release rate – 24,000 cfs
  • Forecast average release rate – 24,000 cfs
  • End-of-March reservoir level – 1840.0 feet
  • Forecast end-of-April reservoir level – 1841.2 feet
     
• Fort Peck Dam
  • Average releases past month – 7,800 cfs
  • Current release rate – 7,500 cfs
  • Forecast average release rate –7,500 cfs
  • End-of-March reservoir level – 2235.7 feet
  • Forecast end-of-April reservoir level – 2236.4 feet

The forecast reservoir releases and elevations discussed above are not definitive. Additional precipitation, lack of precipitation or other circumstances could cause adjustments to the reservoir release rates.

Hydropower:

The six mainstem power plants generated 902 million kWh of electricity in March. Typical energy generation for March is 636 million kWh. The power plants are projected to generate 11.2 billion kWh of electricity this year, compared to the long-term average of 9.4 billion kWh.

To view the detailed three-week release forecast for the mainstem dams, go to http://go.usa.gov/xVgWr.