For the Missouri River, the deep freeze may lie just ahead.
The U.S. Army Corps of Engineers (USACE) is racing against the clock to move remaining flood storage before the river forms ice, officials said Thursday.
South Dakota and Nebraska are bracing for the anticipated arrival of a cold front. By late this weekend, temperatures could plunge to single digits and even sub-zero readings.
The Corps has begun action in anticipation of possible ice jams, USACE spokeswoman Eileen Williamson told the Press & Dakotan.
“The Corps is aware of the potential for cold weather and the formation of ice. This is why we have begun the drawdown to winter flows,” she said.
“This will provide for some extra flexibility to react to the uncertainty of ice-affected river stages.”
This year’s flooding has created near-record runoff, starting with the March bomb cyclone and continuing with consistent summer rainfall. Then, a September deluge inundated parts of southeast South Dakota with upwards of 10 inches of rain in a matter of hours.
As a result, the Corps has continued running Gavins Point Dam releases of 80,000 cubic feet per second (cfs) — one of the highest releases in the dam’s history and triple the normal figure for this time of year.
The Corps has faced challenges moving the remaining flood storage with this year’s near-record runoff, according to John Remus, the chief of the Missouri River Basin Water Management office in Omaha.
Remus and other officials provided an update during a conference call Thursday.
“We are monitoring basin and channel conditions very closely and will make any necessary adjustments. Water remaining in flood control storage zones will lead to increased flood risk in 2020,” Remus said.
“The higher-than-average releases will benefit municipal and industrial water intakes below Gavins Point Dam, which can be impacted by low water levels during periods of ice formation.”
Lower release rates must be set during winter months because the Missouri River ices over in the northern reaches, limiting the amount of water that can flow beneath the ice, the Corps said in a news release.
River ice conditions below all system projects will be closely monitored throughout the winter season. The Corps will also continue to monitor basin and river conditions, including plains and mountain snow accumulation.
The system will receive adjustments based on changing conditions, Remus said.
“We must evacuate the water from the flood control zone before the spring runoff season begins,” he said. “Our plan is to be as aggressive as we can to continue the flexibility in the system.”
The aggressive approach will provide an additional benefit, Remus said.
“The higher-than-average winter releases will provide additional hydropower generation during the winter, which is one of the peak power demand periods,” he said.
The USACE began reducing Gavins Point releases to the winter release rate last Saturday. Even with the drawdown, releases will remain above average, according to Corps hydraulic engineer Mike Swenson.
“The Gavins Point releases (near Yankton) stand at 57,000 cfs, and they’ll be stepped down 3,000 cfs a day until we reach 27,000 cfs in mid-December. We’ll hold that rate through December,” he said.
Currently, Fort Randall releases at Pickstown stand at 48,000 cfs and will be stepped down by 2,000-3,000 cfs per day to reach the winter release rate, Swenson said. The Fort Randall releases are coordinated with downstream Gavins Point.
Despite the runoff challenges, the Corps has made progress in evacuating water, according to Swenson. The system storage stands at 57.3 MAF, a decrease of 3.6 MAF since the end of October.
As a result, the Corps has moved nearly all of the flood water out of the Missouri River system’s flood storage capacity, Swenson said. Currently, the system has 1.2 MAF occupied out of the total 16.3 MAF available for flood storage, he said.
The Gavins Point reductions will continue in January until reaching 25,000 cfs, with releases remaining near that rate for the remainder of winter.
Still, the figure represents about twice the normal winter discharges.
Gavins Point Dam winter releases normally range between 12,000-17,000 cfs, according to the Corps. Higher-than-average winter releases from the Missouri River mainstem system projects, including Gavins Point, continue emptying water from the 2019 runoff season still in storage.
With one month remaining in the year, the Missouri River basin has already nearly matched the record annual runoff above Sioux City, Iowa.
“For the first 11 months of 2019, we have seen 58.8 million acre-feet (MAF), which already makes this the second most runoff in the 121 years of record keeping,” said Kevin Grode, team leader of the Corps’ Reservoir Regulation Division.
The forecast calls for 60.4 MAF of runoff above Sioux City — 238 percent of average — by the end of 2019, Grode said. “If realized, the forecast of 60.4 MAF for the entire year would nearly equal the 2011 mark of 61 MAF,” he added.
With the ground saturated all year, the high runoff has remained a constant throughout 2019, Grode said.
“The November runoff was twice the average, which is continuing the trend of well above average in the basin that we have been experiencing since March,” he said.
South Dakota received heavy snow in late November, which will add to the high runoff, Grode said.
“Our forecast for January and February 2020 are calling for about 1½ times the average for runoff,” he said. “During the last 10 years, January and February runoff has been about 1½ times the average.”
In addition, the mountain snowpack accumulation period is under way, he noted. “We’ll continue to monitor the mountain snow, which normally doesn’t peak until mid-April,” he added.
The past month’s precipitation remained near normal for the lower one-third of the basin, according to National Weather Service (NWS) hydrologist Kevin Low.
“It’s been a bit wetter than normal across South Dakota and eastern Montana,” he said. “The mountain snowpack is about normal, but we’re also mindful that it’s early.”
The Dakotas contain some heavier plains snowpack, with an inch or less of water equivalent, Low said. The NWS doesn’t expect significant weather production during the next week, he added.
“December is calling for above-normal temperatures across the basin and slightly above-normal precipitation,” he said. “For December through February, the odds call for above-normal precipitation to remain in effect.”
Some locations in the basin, such as the James River in eastern South Dakota, are experiencing major flooding, Low said. “Some locations along the (James) river may remain above flood stage through February,” he said.
The Corps’ evacuation of water will benefit areas which have remained flooded since March, Low said. “All locations on the Missouri River are expected to fall below flood stage by later this month, barring unforeseen circumstances,” he said.
Congress has authorized eight purposes in managing the Missouri River, but the Corps has emphasized life and health safety, including flood control, since early 2018, Remus said.
During 2019, managing the Missouri River basin has been very challenging, Remus said.
“People in the basin continue to be seriously impacted, some severely,” he said. “The Corps has tried to make less severe the damage that flooding has caused. We’re doing all we can to reduce the impact.”
Updates on basin conditions, reservoir levels and other topics can be viewed here: https://www.nwd.usace.army.mil/MRWM/MRWMApp/.
Follow @RDockendorf on Twitter.