With the upper basin headed for record runoff, Missouri River dams could continue high releases into November, the U.S. Army Corps of Engineers said Thursday.
Gavins Point Dam near Yankton and Fort Randall Dam at Pickstown will continue some of the highest releases in their history, according to John Remus, chief of the Missouri River Basin Water Management Division.
The announcement was made during a webinar for stakeholders and also a press release.
Remus pointed to the continued high runoff beginning with saturated soil last fall and winter. The situation worsened considerably with the March bomb cyclone which brought intense rainfall over the basin and a breach of Spencer Dam in north-central Nebraska.
Widespread, heavy rainfall has continued for the past six months, prompting the high Missouri River releases, Remus said
"As a result of the high reservoir levels and the forecasted above-average runoff for the remainder of the summer and fall, releases from all system projects will be much above average for the next several months, and possibly as late as November, to ensure evacuation of all stored flood waters prior to the start of the 2020 runoff season," Remus said.
"System releases from Gavins Point Dam are currently 70,000 cfs, which is nearly twice the average release for this time of the year," he added.
The 70,000 cfs at Gavins Point trails only two other instances: the 160,000 cfs for about two months during the historic 2011 flood and the 100,000 cfs for six hours earlier this year.
Fort Randall has maintained releases of 64,000 cfs this year, with the figure scheduled for 64,000-67,000 cfs during the next week.
During August, widespread and heavy rainfall in the upper basin above Sioux City resulted in another month of above-average runoff.
"The Fort Randall and Gavins Point reaches recorded the wettest August in their history," said Kevin Stamm, the Corps’ senior hydraulic engineer.
The Corps will seek to step down the releases at Gavins Point through the end of the year, according to hydraulic engineer Mike Swenson.
"Currently, the basic forecast is holding at 70,000 cfs through September. We’re working to get it down to 62,000 cfs in October and, toward the end of November, work our way to the winter release rate, which we’re showing as 20,000 cfs," he said.
"But that depends on the runoff in the upper basin, which is why we’re looking at holding releases at 70,000 cfs through November. It all depends on runoff."
The Corps faces tremendous pressure to evacuate more than 9 MAF of water through the system to prepare for 2020 runoff, Remus said.
"We’re down to three months to get it done," he said. "An even slightly higher forecast runoff could result in maintaining the 70,000 cfs even longer."
Once ice forms on the river, the Corps has much less opportunity to move water through the system, Remus said.
"We’re limited in the amount of water we can run under the ice, primarily in North and South Dakota but also in Montana to some degree," he said.
Precipitation during August was more than 150% of normal in eastern Montana, portions of North Dakota, much of South Dakota and Nebraska.
While the Fort Randall and Gavins Point reaches experienced their wettest Augusts on record, the Sioux City and Oahe reaches were second and third, respectively.
And the wet weather looks to continue for weeks, according to Kevin Low with the National Weather Service (NWS).
Flooding is still occurring for the James River in eastern South Dakota and the Missouri River’s lower basin, Low said. He anticipates the James River will continue at flood stages for much of the remainder of the year.
The upcoming weather forecast signals more rain, Low said.
"For the next seven days, we are expecting a fairly active weather pattern across the basin with chances for rain almost every day somewhere within the Missouri River basin," he said.
The seven-day forecast calls for one inch or less in some parts of the basin, Low said. At the other extreme, the Dakotas and Montana could see upwards of three inches of rainfall. Localized areas could exceed four or more inches.
"During the entire month of September, most of the Missouri River basin will be trending toward having above-normal precipitation," Low said.
In the upper basin, the prospects for above-normal precipitation continue during the three-month period from September through November. The lower basin doesn’t show any strong indications, with equal chances for above-, below- and normal precipitation.
The 2019 upper basin runoff forecast is 54.6 MAF. If realized, this runoff total would be the second highest runoff in 121 years of record-keeping, only surpassed by 2011 (61.0 MAF) and exceeding the 49.0 MAF observed in 1997.
Accumulated runoff in the lower four reaches — Oahe, Fort Randall, Gavins Point, and Sioux City — was 27.3 MAF. In each of the lower four reaches, the observed runoff exceeded the maximum annual runoff with four months of the year remaining to accumulate additional runoff.
By the end of 2019, the forecasted runoff in these four reaches is roughly 30.0 MAF, which exceeds the average annual runoff for the entire upper basin.
The Corps will meet the situation as it comes, Remus said.
"So much depends on the timing and location of inflows," he said. "We’ll make adjustments as we go."
For updates on basin conditions, reservoir levels and other, visit online at: http://www.nwd-mr.usace.army.mil/rcc/reports/pdfs/weeklyupdate.pdf.
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