Some good news came Tuesday from the managers of the dammed Upper Missouri River that has been inundated by near-record runoff and disastrous flooding the past year.
The focus since March 2018 for the U.S Army Corps of Engineers’ Missouri River Water Management Division in Omaha has been flood control. Historically wet conditions caused billions of dollars of levee damage, thousands of homes destroyed and three lives lost along the Big Muddy’s basin south of Sioux City.
In the Upper Basin, especially in eastern South Dakota, the wet conditions caused many millions of dollars of damages to crops, roads and bridges as well as the lives of several people who drove on flooded roads and bridges and were swept into the water.
The several months of aggressive efforts by the Army Corps to empty the six reservoirs behind the six main-stem dams, including Oahe Dam at Pierre and Fort Pierre, appears to have worked well.
Too well, in a small way.
On Tuesday, Nov. 19, Army Corps officials said a concern lately is that water levels south of Oahe Dam have gotten too low.
Now the Corps' new challenge is to balance the releases from the reservoirs to keep water where it’s needed, while avoiding flooding in other spots. All the while, the Corps is doing the bigger task of getting the whole Upper Missouri Basin system emptied of enough stored water so it can handle next year’s runoff.
During the commission’s regular meeting in Pierre on Monday, Nov. 18, a Hughes County commissioner mentioned how, during a recent drive in south-central South Dakota, surprised he was to see how low the Missouri River is in some places.
It’s an interesting recent change from the long-standing too-much water problem, and it’s been evident to those who check on these things.
The Gavins Point Dam on the South Dakota-Nebraska border is the “bottom” of the Upper Missouri River Basin’s massive drainage system. For two months or more, the Army Corps has been releasing 80,000 cubic feet per second at Gavins Point--more than twice the regular release rate--to get the entire six-dam system emptied enough to handle next year’s runoff.
It’s worked better and faster than expected, especially for Fort Randall Dam just above Gavins Point.
On Tuesday, Nov. 19, John Remus, chief of the Army Corps river management division in Omaha, said in a news release: “Maintaining 80,000 (cfs) from the system would result in a pool elevation at Fort Randall Dam that would potentially impact water supply. Ensuring access for water supply would require increased upstream releases, primarily from the Oahe reservoir, which would cause flooding to critical infrastructure immediately downstream.”
“Critical infrastructure immediately downstream” from Oahe is referring to Fort Pierre and Pierre.
Releases from Oahe have been at the high level of 65,000 cfs for a month or so, which means some wet lawns in Fort Pierre, city leaders there have said.
Fortunately, inflows into the Upper Missouri’s dammed reservoirs since Nov. 1 have been lower than earlier forecasts, according to Remus.
The storage behind the six dams from Gavins Point at the Nebraska-South Dakota border to Fort Peck in northeast Montana, including the two giants: Oahe at Pierre and Fort Pierre and Garrison above Bismarck, has been decreasing faster than expected even as recently as a month ago, Remus said.
So releases from the dams will be reduced, beginning Wednesday, Nov. 20, at Garrison Dam, Friday, Nov. 22, at Fort Randall Dam and on Saturday, Nov. 23, at Gavins Point Dam.
Releases from Oahe, meanwhile, will remain at 65,000 cfs — to help boost Lake Francis Case’s water level — until Dec. 2 when it will be reduced to 60,000 cfs, then to 55,000 cfs on Dec. 3 and 50,000 cfs on Dec. 5, according to the Corps.
The six-reservoir system was down to 58.6 million acre-feet (MAF) on Tuesday, Nov. 19. Of that total, only 2.5 MAF was from the flood control “top” zone of the reservoirs that the Corps wants “evacuated by next spring." That 2.5 MAF is 15 percent of the system’s 16.3 MAF of flood control storage. Getting it out of the system by the end of winter looks more feasible than things looked two or, even, one month ago, according to Corps’ officials.
At current conditions, including the newly announced release reductions, the system’s total storage will be down to 57.4 MAF by Nov. 30, about 0.3 MAF lower than was projected Nov. 1, Remus said on Tuesday. The goal of lowering the reservoirs’ storage is 56.1 MAF which will give the Corps — and the Upper Basin — the full space of 16.3 MAF normally thought to be enough to handle runoff next year.
Even with the planned release reductions, system storage is expected to fall from the 58.6 MAF reported on Tuesday, Nov. 19 to 57.4 million acre feet by Nov. 30, approximately 0.3 MAF lower than was projected in the Nov. 1 forecast.
A big reason is that the runoff projections for this year are being lowered. In October, the Corps was figuring the total 2019 runoff would tie the record of 61 MAF seen in the big flood year of 2011.
That projection was cranked down by Nov. 1 to 60.2 MAF and will be updated again at the end of November, Corps river management division spokeswoman Eileen Williamson told the Capital Journal.
Inflows into Lake Oahe in recent days have been just above the 50,000 cfs level, as a daily average. It is projected to start dropping off later this week until it hits only 25,700 cfs by Dec. 6, according to Corps documents.
It looks positive along the Upper Missouri system now to have the reservoirs ready for next year’s cycle of mountain snow pack melt with the prairie snow melt and the precipitation.
The recent relatively dry weather across the Basin region means the Army Corps’ aggressive release schedule has been successful.
“The good news is there is less water coming into the system,” Williamson told the Capital Journal in an email response to questions. “So to be projecting that we will be at 57.4 MAF (of total storage in the system) by the end of November means that we will be on track to get the additional 1.3 MAF out by mid-January.”
Remus added a cautionary note that about the dynamic nature of the river management and how fragile much of the Missouri River Basis remains from eastern South Dakota south into Kansas and Missouri.
“It is important to understand flooding can and will occur regardless of available reservoir storage space,” Remus told the Capital Journal on Tuesday via email. “As we head into the winter and next spring, levees will not be fully restored and the ground remains very saturated. Given these conditions, we will be as aggressive as we can in the spring to provide the greatest amount of flexibility in the system.”