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Melting snow and rain ends with record runoff in river basin

Posted: 1:46 PM, Apr 03, 2019
Updated: 2019-04-03 18:46:23Z
Missouri River Basin Update

OMAHA, Neb. (KMTV) — The Army Corps of Engineers says snow and rain melt off have inundated the Missouri River Basin above Sioux City, Iowa. The previous record was 7.3 million acre feet...the new record is 11.0 million acre feet.

The Corps says their runoff forecast was off by quite a bit due to the higher-than-average water levels. In fact, they say it was more than 151 percent more than normal.

You can read the full release below:

March runoff in the upper Missouri River Basin above Sioux City, Iowa, was a record 11.0 million acre feet , surpassing the previous record of 7.3 MAF set in 1952. The average March upper basin runoff is 2.9 MAF.

“The record March runoff significantly altered our 2019 upper basin runoff forecast,” said John Remus, chief of the U.S. Army Corps of Engineers Missouri River Basin Water Management Division.

“Our runoff forecast increased to 38.2 MAF, which is 151 percent of normal. The March runoff was nearly 4 times the average. Runoff in the Fort Randall Dam to Gavins Point Dam reach was nearly twice the record highest March runoff. March runoff in the Gavins Point to Sioux City reach was more than that reach typically sees during a year,” said Remus.

The record high runoff in March was caused by 2-4 inches of rain falling on heavy plains snowpack causing the snowpack to rapidly melt on frozen, saturated soils. Pool levels in the four System projects that have significant flood control storage – Fort Peck, Garrison, Oahe and Fort Randall – have all increased significantly to capture much of the runoff. The Corps plans to increase Gavins Point releases to 55,000 cubic feet per second by early next week. Gavins Point releases will be above average for the next several months, and possibly as late as November.

“We need to reduce pool levels in Oahe and Fort Randall over the next several weeks so that those reservoirs are in position to reduce flood risk during the spring and summer. The Fort Peck and Garrison reservoirs are well positioned to receive the runoff from the mountain snowmelt, which typically begins in May,” added Remus.

As of April 1, the mountain snowpack was 97 percent of average in the reach above Fort Peck and 93 percent of average in the reach from Fort Peck to Garrison. Normally the mountain snowpack peaks in mid-April. View the mountain snowpack graphic here: http://www.nwd-mr.usace.army.mil/rcc/reports/snow.pdf .

Much of the plains snowpack in central North Dakota and eastern South Dakota has melted. The heaviest snowpack remains in isolated areas of north central South Dakota and south central North Dakota where the snowpack’s liquid content, or snow water equivalency (SWE), ranges from 1 to 5 inches. Frost depth is still deep in much of the upper basin, including the areas with the remaining snowpack. The Corps is cooperating with other agencies to acquire plains snow measurements in the upper basin.

Based on the March 15 System storage check, flow support for the first half of the navigation season is full service. However, due to above average runoff into Oahe and Fort Randall reservoirs, releases from Gavins Point have been above full service levels to lessen the time that those projects have water stored in their exclusive flood control zones. 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. Flow support is generally sufficient to provide a 9-foot-deep by 300-foot-wide channel.

Weekly updates on basin conditions, reservoir levels and other topics of interest can be viewed here: http://www.nwd-mr.usace.army.mil/rcc/reports/pdfs/weeklyupdate.pdf .

The Corps will host six public meetings April 9-11 to discuss the Missouri River Mainstem System, its runoff and reservoir operations. Meeting information is detailed in a separate news release: https://go.usa.gov/xmqSp .

Monthly Water Management Conference Calls

Due to the spring public meetings that will be held April 9-11, the fourth monthly conference call of the 2019 runoff season will be held May 7 to inform basin stakeholders on current weather and runoff forecasts and the planned operation of the System. Presentation materials will be posted on the MRBWM website at: http://www.nwd-mr.usace.army.mil/rcc/ . The call is intended for Congressional delegations; Tribes; state, county and local government officials; and the media. It will be recorded in its entirety and made available to the public on the Defense Video and Imagery Distribution System at www.dvidshub.net/unit/usace-nwd .

Reservoir Forecasts

Gavins Point Dam

  • Average releases past month – 30,600 cfs
  • Current release rate – 39,000 cfs
  • Forecast release rate – 55,000 cfs early next week
  • End-of-March reservoir level – 1205.4 feet
  • Forecast end-of-April reservoir level – 1206.0 feet

Fort Randall Dam

  • Average releases past month – 11,600 cfs
  • End-of-March reservoir level – 1366.9 feet (up 16.2 feet from February)
  • Forecast end-of-April reservoir level – 1360.5 feet
  • Notes: Releases will be adjusted as necessary to maintain the desired reservoir elevation at Gavins Point.

Big Bend Dam

  • Average releases past month – 15,100 cfs
  • Forecast average release rate – 32,100 cfs
  • Forecast reservoir level – 1420.0 feet

Oahe Dam

  • Average releases past month – 9,500 cfs
  • Forecast average release rate – 31,400 cfs
  • End-of-March reservoir level – 1614.7 feet (rising 7.9 feet during March)
  • Forecast end-of-April reservoir level – 1616.0 feet

Garrison Dam

  • Average releases past month – 13,100 cfs
  • Current release rate – 13,000 cfs
  • Forecast average release rate – 13,000 cfs
  • End-of-March reservoir level – 1842.6 feet (rising 5.3 feet during March)
  • Forecast end-of-April reservoir level – 1845.0 feet

Fort Peck Dam

  • Average releases past month – 6,500 cfs
  • Current release rate – 6,500 cfs
  • Forecast average release rate – 6,500 cfs
  • End-of-March reservoir level – 2238.1 feet (up 3.7 feet from February)
  • Forecast end-of-April reservoir level – 2240.1 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.
The six mainstem power plants generated 473 million kWh of electricity in March. Typical energy generation for March is 639 million kWh. The power plants are projected to generate 11.9 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://www.nwd-mr.usace.army.mil/rcc/reports/twregfcast.pdf .

MISSOURI RIVER MAINSTEM RESERVOIR DATA

Pool Elevation
(feet above mean sea level)

Water in Storage
(1,000 acre-feet)


On March 31
Change in March
On March 31
% of 1967-2018 Average
Change in March
Fort Peck
2238.1
+3.7
15,672
108
+798
Garrison
1842.6
+5.3
19,392
109
+1,703
Oahe
1614.7
+7.9
21,065
119
+2,606
Big Bend
1420.7
+0.1
1,671
98
+2
Fort Randall
1366.9
+16.2
4,489
134
+1,436
Gavins Point
1205.4
-0.4
314
80
-10


Total
62,603
113
+6,535

WATER RELEASES AND ENERGY GENERATION FOR MARCH

Average Release in 1,000 cfs
Releases in 1,000 acre-feet
Generation in Million kWh
Fort Peck
6.9
426
65
Garrison
16.7
1,030
156
Oahe
9.5
583
85
Big Bend
15.1
927
53
Fort Randall
11.6
714
78
Gavins Point
30.6
1,879
36

Total
473