Citing water supply concerns, the U.S. Army Corps of Engineers (USACE) has cut Gavins Point Dam releases to 27,000 cubic feet per second (cfs) starting today (Wednesday).
The Corps is evacuating water from the Missouri River reservoirs to prepare for the 2020 runoff season. The upper basin above Sioux City, Iowa, has seen near-record runoff during the past year, making it more difficult to evacuate water out of the reservoirs.
The announcement Tuesday marks the second adjustment this month at the dam near Yankton.
On Jan. 7, the Gavins Point releases near Yankton were increased to 30,000 cfs from the previous 27,000 cfs.
Since that time, the total storage at Gavins Point declined by 124,000 acre feet. The pool elevation dropped from 1207.7 feet to 1201.9 feet — raising questions about the available water supply for some communities on the river.
“The pool level fluctuations at Gavins Point Dam have led to concerns that the lower pool level may affect access to water at some municipal water intakes on Lewis and Clark Lake,” said John Remus, chief of the Missouri River Water Management Division.
The action will help stabilize Gavins Point’s pool elevation, Corps officials said.
The reduced releases will hold back more water behind the dam near Yankton for a longer period. In turn, the reservoirs will contain more water for communities that use the river for their water supply.
Currently, the B-Y Water District has remained able to meet its needs, according to Manager Terry Wootton.
“B-Y Water District has no issues regarding the Corps discharges and has more than enough water supply,” Wootton told the Press & Dakotan in an email.
According to its website, B-Y serves seven counties: Bon Homme, Hutchinson, Yankton, Douglas, Turner, McCook and Hanson.
B-Y serves the following towns and cities in bulk: Avon, Freeman, Tyndall, Irene, Lesterville, Menno, Utica, Mission Hill, Parkston, Scotland, Tabor, Volin, Mitchell, TM Rural Water District and Hanson Rural Water System.
In addition, B-Y serves individual customers in the towns of Olivet, Dimock and Kaylor.
While the Corps’ action marks a slight downturn for Gavins Point, it’s still nearly twice the average releases of 12,000-17,000 cfs for this time of year.
Higher-than-average releases have been the norm during the past year in response to massive and prolonged flooding in South Dakota and Nebraska.
Last March, the Corps tripled the Gavins Point releases to 100,000 cfs — one of the highest figures on record for the dam — in a 24-hour period as unregulated flows from the Niobrara River and other watersheds poured into the reservoir.
The Corps maintained a Gavins Point flow of 80,000 cfs for much of the latter half of 2019.
The Missouri River basin could see renewed flooding this year because of saturated soil and large amounts of snowpack.
National Weather Service (NWS) hydrologist Mike Gillispie said he will know more details Thursday when he issues his next 90-day outlook, but he sees a developing trend.
“For now, we’re looking at above- to much-above normal snowpack for this time of year … (We’re also looking at) still increased chances for flooding this spring for all area rivers and streams, even with normal temperatures and precipitation going forward,” he told the Press & Dakotan.
“In general, we have 4 to 10 inches of snow between the Missouri River (on the South Dakota-Nebraska border) and I-90 with 1 to 3 inches of water content. Areas along and north of I-90 have 10-18 inches of snow depth with 2 to 4 inches of water content.”
The National Weather Service (NWS) in Sioux Falls reported most locations in the quad-state area received 4-8 inches of snow by the time a significant winter system moved out of the region Saturday.
Yankton recorded 4.5 inches, according to the NWS.
The Sioux Falls municipal airport led with 8.1 inches, followed by Huron with 7.8 inches. Other large amounts in the area included Mitchell 6.8 inches, Hurley 5.8 inches, Ponca, Nebraska, with 5.5 inches; Menno and Pickstown, 5 inches each; Sioux City 4.8 inches; Elk Point and Montrose, 4.5 inches each; Academy, Tyndall and Emery, 4 inches each; Dimock, 3.7 inches; and Lake Andes, 3 inches.
Mountain snowpack continues to accumulate at near average rates, while Plains snowfall over the past week has led to increased accumulations in central and eastern North and South Dakota, according to the Corps.
The mountain snowpack accumulation period is about 50% complete, the Corps said. The mountain snowpack normally peaks near April 15.
“Releases from all projects will be higher than average during the remainder of the winter,” Remus said. “We will continue to monitor conditions and remain aggressive in our releases, to the extent it is practicable.”
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