Significant rainfall led to an above average runoff in the upper Missouri River Basin. June runoff was 6.6 million acre-feet, which is 119% of average and 2.6 MAF higher than forecast.

A strong weather system moved into the basin on June 21 producing excessive rainfall in eastern South Dakota, north central and northeastern Nebraska, and northwestern Iowa. The rainfall totals exceeded 600% of normal over the 24-hour period.

“In response to the rainfall, the releases from Fort Randall and Gavins Point dams were reduced,” said John Remus, chief of the Missouri River Basin Water Management Division. “The lower releases were able to reduce downstream river stages, but they could not completely offset all of the flooding in the Sioux City area.”

Rainfall persisted into the following week causing sustained high inflows both into Gavins Point as well as the river downstream. Releases were reduced at Fort Randall Dam to an average of 2,000 cubic feet per second and Gavins Point to 24,000 cfs. The lowered releases in conjunction with the high inflows caused both reservoir pools to rise, reaching elevation 1360.8 feet at Fort Randall and 1209.6 feet at Gavins Point.

“During that time, some of the outflow from Gavins Point Dam was transferred from the powerhouse to the spillway, allowing us to store more water in Gavins Point Reservoir and maintain the release rate at 24,000 cfs,” added Remus.

As the inflows into Gavins Point continued to fall and the reservoir level began to decline, the spillway was closed and the release rate from the dam was stepped down to mitigate flood impacts downstream. Releases from Gavins Point Dam reached 13,000 cfs on June 28, and remain at that rate.

“As the river continues to recover from the flood event, we will continue to monitor inflows and pool elevations at Gavins Point, and throughout the Missouri River Mainstem System, and make adjustments as needed,” said Remus.

The 2024 calendar year runoff forecast for the upper Missouri River Basin above Sioux City, Iowa is 24.6 MAF, 96% of average and 3.6 MAF higher than last month’s forecast. June runoff in the Gavins Point to Sioux City reach was nearly seven times normal. While the eastern portion of the basin received excessive rainfall, other portions were drier than normal with below average runoff in the Fort Peck, Garrison, and Oahe reaches. Soil moisture at the end of June is near normal in central Montana, below normal in western South Dakota, and above normal in the eastern Dakotas. Currently, 50% of the Basin is experiencing abnormally dry or drought conditions.

System storage on July 1 was 56.6 MAF, 0.5 MAF above the top of the carryover multiple use zone. “Based on the July 1 System storage, flow support for navigation will be maintained at 500 cfs below full-service level,” said Remus. “Per the guidelines in the Master Manual, this will also result in a full navigation flow support season ending December 1 at the mouth of the Missouri River. Gavins Point releases will be adjusted through the month of July to account for the navigation flow support.” Basin and river conditions continue to be monitored and System regulation will be adjusted based on the most up-to-date information.

Navigation:

Gavins Point Dam releases will be set to provide flow support at an intermediate-service level, 500 cfs lower than full-service flow support at all four target locations (Sioux City, Omaha, Nebraska City, and Kansas City). Navigation flow targets may be missed in reaches with no commercial barge traffic. The flow support season length will be a full 8-month season, ending December 1 at the mouth of the Missouri River.

Mountain Snowpack:

Mountain snowpack in the upper Missouri River Basin melted quickly due to warmer-than-normal temperatures during the spring and early summer. By June 25, all the snow had melted in both the reach above Fort Peck Dam and the Fort Peck Dam to Garrison Dam reach. The mountain snowpack peaked in the reach above Fort Peck on April 9 at 73% of average, while the mountain snowpack in the Fort Peck to Garrison reach peaked on April 10 at 82% of average. Mountain snowpack normally peaks near April 17. The mountain snowpack graphics can be viewed at: http://go.usa.gov/xARQC.

Fort Peck Flow Test:

Test releases from Fort Peck to assess the potential benefits of alternative management scenarios for the pallid sturgeon began on April 26 and will be completed by Sept. 1. The test includes two higher flow periods, in late April and June, with target flows at Wolf Point, Montana. The first peak in releases was completed in early May with peak flows of 18,000 cfs at Wolf Point, Montana. Releases were reduced to 10,000 cfs by May 10. The second peak began on June 19 and reached a peak flow of approximately 20,000 cfs on June 26. Flows are currently declining at a rate of 1,000 cfs per day and should reach an average daily flow of 8,000 cfs around July 7. The plan is to hold this flow through September 1. After September 1 operations at Fort Peck will return to normal.

The U.S. Army Corps of Engineers will host weekly virtual meetings during the flow test to update the public on test progress and planned operations. Information on accessing the public meetings can be found at https://www.nwd.usace.army.mil/MRWM/Public-Meetings/Meetings. Call will be held on Wednesdays at 1 p.m. Central (12 p.m. Mountain).

During the flow test a number of monitoring activities will be conducted to include fish monitoring, lidar and aerial photography, physical surveys, cultural resource surveys, and water quality sampling. Interested parties can also provide information through a web-based application that can be found at https://hydroviz.ca/fort-peck-feedback.

Monthly Water Management Conference Calls

Water management calls include an update from the National Weather Service’s Missouri Basin River Forecast Center, and an update on the Missouri River mainstem reservoir system operations. The next call will be held Thursday, July 11. All calls are recorded in their entirety and are available to the public on our website at https://go.usa.gov/xARQv.

Reservoir Forecasts:

Gavins Point Dam

o Average releases past month – 26,000 cfs

o Current release rate – 13,000 cfs

o Forecast release rate – 16,800 cfs

o End-of-June reservoir level – 1207.0 feet

o Forecast end-of-July reservoir level – 1206.0 feet

o Notes: The Gavins Point release will be adjusted to mitigate flooding and provide navigation flow support on the lower Missouri River.

Fort Randall Dam

o Average releases past month – 19,000 cfs

o End-of-June reservoir level – 1360.1 feet (up 4.7 feet from May 31)

o Forecast end-of-July reservoir level – 1358.1 feet

o Notes: Releases will be adjusted as necessary to maintain the desired reservoir elevation at Gavins Point and to back up Gavins Point releases.

Big Bend Dam

o Average releases past month – 22,700 cfs

o Forecast average release rate – 11,700 cfs

o Forecast reservoir level – 1420.6 feet

Oahe Dam

o Average releases past month – 22,800 cfs

o Forecast average release rate – 11,900 cfs

o End-of-June reservoir level – 1603.0 feet (no change since May 31)

o Forecast end-of-July reservoir level – 1605.6 feet

Garrison Dam

o Average releases past month – 21,600 cfs

o Current release rate – 22,000 cfs

o Forecast release rate – 22,000 cfs

o End-of-June reservoir level – 1842.2 feet (up 4.4 feet from May 31)

o Forecast end-of-July reservoir level – 1842.3 feet

o Notes – Releases will be maintained at 22,000 cfs through mid-September.

Fort Peck Dam

o Average releases past month – 13,700 cfs

o Current release rate – 12,000 cfs

o Forecast average release rate – 8,000 cfs

o End-of-June reservoir level – 2230.2 feet (down 1.4 feet from May 31)

o Forecast end-of-July reservoir level – 2229.2 feet

o Notes: Releases will be adjusted in accordance with the Fort Peck flow test.

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 775 million kWh of electricity in June. Typical energy generation for June is 843 million kWh. The power plants are expected to generate 7.8 billion kWh 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 https://go.usa.gov/xARQB.

The Missouri Basin Web App provides links to these reports and others that are updated more frequently. http://go.usa.gov/xE6fC