Storage (runoff) news: Lake Nighthorse 20% full

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From The Durango Herald (Dale Rodebaugh):

As of Wednesday the dam was holding back 25,000 acre-feet of water, slightly more than 20 percent of its capacity. The deepest point in the lake was 95 feet, with 87 vertical feet to go, Artichoker said. The amount of water the Bureau of Reclamation can take from the Animas River for Lake Nighthorse, one component of the Animas-La Plata Project, depends on the flow in the river. From April through September the agency must allow a minimum flow of 225 cubic feet per second below the pumping plant to satisfy the demands of downstream water-right holders and provide water for fish species; in October and November, the minimum flow is 160 cfs; and December through March, 125 cfs.

On Wednesday, the Animas flow peaked at 483 cfs, down from 766 cfs a week ago, 1,110 cfs two weeks ago and 2,110 cfs on July 1. Since frequent rain has done little to boost the flow, the Bureau of Reclamation has limited the amount it pumps to Lake Nighthorse, just over a ridge to the southwest from Bodo Industrial Park. The current 225 cfs downstream demand would allow the agency to pump considerably more than the 110 cfs it was taking on Wednesday.

Pumping into Lake Nighthorse will cease in August for 30 days. The hiatus will allow for saturation of the core of the earth-filled dam and give engineers a chance to check filling criteria devised by dam designers and safety engineers. “We don’t want to shock the dam by putting a big load on it all of a sudden,” Artichoker said. “We want to ease the dam into its function.” Piezometers will measure water level; inclinometers will show if there is settling or bending in the structure; brass embankment measurement points on the top of the dam also measure settlement; and a toe-drain system on the downstream side of the dam will indicate if there is seepage. “Information so far tells us that this dam is really tight, but we want to see if it’s performing as anticipated,” Artichoker said. “There won’t be any pumping, but there will be monitoring done 24/7.”

More Coyote Gulch Animas River watershed coverage here and here.

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