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Flooding Expected to Continue as Dam Flows Raised


The likelihood of more prolonged flooding along the Missouri River increased Thursday night when the Army Corps of Engineers was forced to increase water releases from Gavins Point Dam in South Dakota to 90,000 cubic feet per second because of inflows from the Niobrara River and other watersheds, the Corps stated.

Releases from Gavins Point quickly spiked from 17,000 cfs just a few days ago to 37,000 cfs on Thursday morning. By Thursday evening, the Corps had nearly tripled the release levels. Corps officials anticipate they will be able to scale back water releases from the dam once inflow from the Niobrara River begins to slow.

In Nebraska, major flooding remains along several larger tributaries into the Missouri River. It was a similar situation in western Iowa where the town of Hornick, south of Sioux City, was evacuated because a levee breach and tributaries in southwest Iowa such as the Boyer and Nishnabotna Rivers were significantly flooded.

Updated flood forecasts along the Missouri River by the National Oceanic and Atmospheric Administration (NOAA) showed the river at Plattsmouth, Nebraska, was at 37.15 feet, a record high; Nebraska City, Nebraska, was also at a record high; and Brownville, Nebraska, was at 42.67 feet and could top the record high of 44.79 feet set in the 2011 flood. The river stages were already projected to top record flooding levels before Gavins Point increased its water releases.

The Corps stated operators at Gavins Point are using 12 of the dam’s 14 spillway bays and the powerhouse to pass the flows. The remaining two spillway gates are partially open, but frozen in place due to ice buildup. Operators are spilling water over those two gates in an effort to thaw them and return them to operating condition, which dam safety engineers believe presents no risk to the structure or the gates, nor does it affect the Corps’ ability to safely pass water pass the structure.

The water being released from Gavins Point is exclusively from unregulated tributaries that bring water into the reservoir, the Corps stated. On Wednesday, the Corps stopped all releases from Fort Randall Dam, the next dam upstream on the Missouri River mainstem, to reduce the amount of water in the lower Missouri River. However, because there is little storage capacity behind Gavins Point, most of what is flowing into the reservoir must be released downstream.

“Given the amount of water still expected to come out of the tributaries, we expect we will hold at 90,000 cfs through Saturday morning, provided the current inflow trends are maintained,” said John Remus, chief of the Corps’ Missouri River Water Management Division in Omaha. “As that unregulated runoff decreases, we will be able to decrease outflows from Gavins Point.”

Remus cautioned, however, that river levels could remain high in places for several days to a week as conditions in the different basins normalize.

Source: DTN

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