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July 16, 2008 6:07 pm

Buffalo Bill almost full as run-off season ends

Written by Tribune Staff

Cascading into the canyon

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Visitors to the Buffalo Bill Dam Visitor Center are witness to a show of water power from the walk-way above the dam. The releases from a nearly-full reservoir fill the canyon with mist, creating a rainbow in the afternoon sunlight as swallows glide between the canyon walls. Tribune photo by Dave Bonner

It's been a good water year for the Shoshone River Basin.
A good snowpack in the mountains this spring, and wet weather in late May and June, resulted in a spring runoff well above average and a nearly-full reservoir behind Buffalo Bill Dam.
As of Tuesday, the reservoir was more than 95.4 percent full, less than four feet from its capacity.
John Lawson, Bureau of Reclamation area manager for Wyoming, said the spring runoff in the basin has exceeded predictions. On May 1, the bureau had forecast a total runoff during the April through July period of 720,000 acre feet.
“But then it caught us by surprise. All of a sudden we got a lot of snow in May,” Lawson said. “I think (the runoff) will probably end up around 950,000 acre feet.”
The heavy runoff forced the Bureau to increase discharge through the dam to make room for the new water as average daily inflow into the reservoir rose to nearly 11,000 cubic feet per second in late June.
Bryant Startin, manager of the Shoshone Irrigation district, said the heavy runoff was welcome after last year's relatively dry year.
“Last year they never had to dump water,” Startin said.
Startin called this year “more of a typical year” for runoff in the Shoshone Basin, and data from the Bureau of Reclamation bear that out. Snow pack in the drainage above the lake was close to average through most of the water year, which began Oct. 1, and was higher than average through most of May and June.
Last year, by contrast, the snowpack was well below average through the winter and the runoff ended in mid-June, a month earlier than this year.
The heavy runoff season is ending now, and inflows over the past two weeks have dropped from nearly 9,800 cfs to around 4,000 cfs. Lawson said he has adjusted outflows accordingly this week and he plans to inch the reservoir closer to its full capacity. Tuesday, the outflow was reduced to less than 3,800 cfs, about 200 cfs less than the inflow
The lake is currently approximately 3 1/2 feet from its full level, and Lawson said he wants to raise the level about two more feet.
Lawson said he is reluctant to raise the lake to its full level because the lake was not designed with a flood control pool. When the lake is at its official capacity, it is only 1 1/2 feet from the top of the dam, and “one good rainstorm on the North Fork” could overfill the reservoir.
“I like to leave at least a small space there,” Lawson said. “It's a guessing game.”
Both Startin and Lawson said this spring's runoff should provide for irrigation needs this summer and leave the lake at a healthy level this fall.
Lawson added that the conditions should allow him to maintain a release of 350 cfs through the winter, which will benefit fish in the river. In recent years, winter releases have been held at 150 to 200 cfs based on an formula worked out among various groups with interests in the lake and the river, including the Wyoming Game and Fish Department.
“It's good to be able to satisfy all the interests in the river,” Lawson said.