The Army Corps of Engineers (Corps) held an ad-hoc conference call on May 29 with governmental entities and members of the press to update them on current runoff conditions and operational decisions being made in response to those conditions. John Remus, Chief of the Missouri River Basin Water Management Division at U.S. Army Corps of Engineers, Northwestern Division, told attendees conditions were dictating another increase in releases from Gavins Point Dam, and the rate would be raised to 75,000 cubic feet per second (cfs) on Saturday, June 1.
Kevin Grode of the Corps advised there has been a tremendous amount of precipitation in both the upper and lower Missouri River basin over the last two weeks. Some areas have received four to six times normal precipitation in that time period. Exacerbating problems is the fact that a large part of the river basin is retaining 95-98 percent soil moisture. The high soil moisture means the torrential rains are not infiltrating the ground, but immediately becoming runoff.
Runoff in May so far has been record-setting, and the last three months together have produced 26.3 million acre feet (MAF) of runoff, an amount equal to an entire year’s worth of runoff normally.
Remus said the lower four reservoirs in the system in particular were full or nearly so, and mountain snowpack is still melting.
Based on lack of space in the reservoir system, and continuing inflows from tributaries, Remus said Gavins Point Dam releases, which had just been raised by 5,000 cfs on Tuesday and again on Wednesday, would need to be raised again, to 75,000 cfs on Saturday, June 1.
Remus did say the three week forecasts the Corps had run on Tuesday and Wednesday had indicated this need, but if the situation looked better by Saturday, they might not need to make the increase after all.
When questioned about steps being taken to mitigate current flooding of roads and towns in southwest Iowa and elsewhere, presenters pointed out only one third of the current river level at Nebraska City (for example) was caused by waters released from Gavins Point; the rest was coming from tributaries uncontrolled by the Corps. Another presenter stressed that floods can and will occur regardless of Corps dam operations.
One listener questioned if the flooded conditions in the lower portion of the Missouri River Basin were dictating releases from Gavins Point. Remus explained the Oahe and Fort Randall reservoirs were both very high and expected to go higher, and managing those pools played a big part in releases from Gavins Point.
A South Dakota listener questioned why Oahe releases weren’t increased earlier. Presenters explained they couldn’t ramp up Oahe releases because Fort Randall was full. Added to this problem, there was a lot of water coming into the system from the Niobrara, which was preventing the Corps from raising Fort Randall releases to the level they wanted to.
Remus said he didn’t foresee a problem from melting mountain snowpack, but how much other water might flow into the upper basin was a "wild card."
Grode reminded everyone the basin was just starting to see the impact of mountain snowpack runoff; that impact would be seen in June for Fort Peck and Garrison.
Only the next few months will show what impact mountain snowpack runoff coupled with ongoing rainfall and input from tributaries may have in the lower basin.
Remus said of the planned 75,000 cfs releases (a release amount nearly double the normal 35,000 cfs releases for this time of year), "I’m confident we will have to have at least the releases mentioned. I don’t think it will be less, and I hope it’s not significantly more."
The Corps is currently posting daily updates on their website and on Facebook, and Fremont County Emergency Management Director Mike Crecelius also shares this information on his Facebook page daily.
The most recent three week forecast (May 31) shows Fort Randall and Oahe reservoirs already full to the exclusive flood control zone, Garrison reaching that point by June 10, and Fort Peck reaching the exclusive flood control level by June 14. Planned releases indicate the Nebraska City river stage will remain over two feet above flood stage through June 14 at least. These numbers and expectations are also revised with each Corps update.
The next governmental and media update webinar will take place on June 6.