Riverdale, N.D. --
Garrison Dam releases averaged 36,800 cubic feet per second (cfs) during May, ranging from 32,000 cfs to 39,000 during the month.
On June 7, due to the forecasted rapid rise in reservoir elevations, releases were increased to 44,000 cfs. The reservoir is currently forecasted to peak at or below elevation 1851.5 ft. within approximately the next two weeks, followed by significantly reduced inflows, as runoff from the remaining mountain snowpack tapers off.
In order to meet the 44,000 cfs release, the Garrison Project initiated releases of 3,000 cfs through its regulating tunnels. This release supplements the 41,000 cfs release through the power plant for a combined release of 44,000 cs.
The 44,000 cfs release rate is expected to continue through mid-July as water is evacuated from the exclusive flood control zone which is between elevations 1850.0 and 1854.0. The recent increase in releases is expected to increase the river stage near Bismarck by less than one foot.
The river stage is expected to remain at or below 11 feet at the Bismarck gage. Without the Garrison Dam in place, flows on the Missouri River through the Bismarck/Mandan reach would have exceeded 100,000 cfs this past week.
With the releases through the regulating tunnels, public access to the wing walls is being restricted to the western most wing wall. However, the west tailrace access will remain fully open to the public.
Boaters in the tailrace are reminded that it is illegal, and unsafe, to boat beyond the orange line painted on the rocks on both banks of the tailrace at Garrison Dam. Water turbulence and backflows toward the power plant create unsafe conditions so boating is prohibited upstream of the orange line, or within 200 feet of the power plant.
As of June 1, the mountain snowpack was 91 percent of average in the reach above Fort Peck and 88 percent of average in the reach from Fort Peck to Garrison. The mountain snowpack peaked on April 19 in the Fort Peck reach and on April 15 in the Fort Peck to Garrison reach.
Compared to 2011, the mountain snowpack in 2018 had a lower peak snow water equivalent in both reaches and melted earlier. Both reaches have less than 6.0 inches of snow water equivalent remaining while at this same time in 2011, there were 19 inches remaining above Fort Peck and 22 inches remaining in the Fort Peck to Garrison reach.
View the mountain snowpack graphic here: https://www.nwd-mr.usace.army.mil/rcc/reports/snow.pdf.
Weekly updates on basin conditions, reservoir levels and other topics of interest may be viewed here: https://www.nwd-mr.usace.army.mil/rcc/reports/pdfs/weeklyupdate.pdf.
To view the detailed three-week release forecast for the mainstem dams, go to: https://www.nwd-mr.usace.army.mil/rcc/reports/twregfcast.pdf.