High runoff anticipated

Posted 4/14/11

The Shoshone River Basin is at 121 percent, according to the National Resource Conservation Service Monday report.

By contrast, one year ago, the snowpack in the Shoshone River Basin stood at 64 percent of average, according to the …

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High runoff anticipated

Posted

Buffalo Bill Reservoir capacity considered

Mountain snow is above average this year, so Buffalo Bill Reservoir managers are keeping an eye on snowpack in the hills, and they may release more water from the dam.

Big Horn Basin-wide, snowpack was 120 percent of average as of Monday, said Jim Fahey, National Weather Service hydrologist in Riverton.

The Shoshone River Basin is at 121 percent, according to the National Resource Conservation Service Monday report.

By contrast, one year ago, the snowpack in the Shoshone River Basin stood at 64 percent of average, according to the NRCS.

Natural Resource Conservation Service averages are based on a 30-year period from 1971-2000.

A few weeks ago, snowpack was at 107 percent for drainages flowing into the Shoshone River and Buffalo Bill Reservoir. By April 1, it had increased to 121 percent, said John Lawson, Bureau of Reclamation area manager for Wyoming.

Right now, the dam at Buffalo Bill is releasing 2,500 cubic feet per second, but managers may increase the discharge in late April or May to create space for anticipated spring runoff, Lawson said.

The reservoir’s capacity is 646,000 acre feet. They are anticipating the arrival of 840,000 acre feet from April 1 through July 30, Lawson said.

The bureau prefers to keep the reservoir’s capacity at around 630,000 acre feet to allow for a sudden storm in the high country.

In 2009, managers expected 840,000 acre feet of water but received 950,000 from April through July. Precipitation downstream from the reservoir, coupled with 700,000 cfs dam releases in June 2009 caused minor flooding downstream around Lovell, Lawson said.

“We don’t want to have those same problems we had in 2009,” Lawson said. “We’re taking actions early this year.”

Snowpack on the west side of the Big Horn Mountains is 105 to 120 percent of normal and the east side is at 125 to 145 percent of normal, according to the Natural Resource Conservation Service.

Big Horn Reservoir now holds 846,000 acre feet, making it 79 percent full, Lawson said.

“In response to reservoir inflows and further increases in mountain snowpack over the past weekend, and consistent with the provisions of the Draft Yellowtail Operating Criteria, Reclamation will be increasing releases to the Bighorn River later this week from the current rate of 3,750 cubic feet per second to approximately 4,750 cubic feet per second. Additional adjustments in releases throughout the upcoming weeks are probable as the runoff picture continues to develop,” said Dan Jewell, BuREC Montana area manager in an email to the Tribune.

As of Monday, Sylvan Pass had 143 percent of average snowpack and the Northeast Entrance stood at 146 percent of normal, Fahey said.

Those increases were mirrored across the state, as every basin except one experienced an increase, and the statewide average jumped from 116 percent to 122 percent of average.

The only basin in the state that decreased was the Belle Fourche in northeastern Wyoming, and even that basin was at 100 percent Monday morning.

“There is not going to be any problem with water supply,” Fahey said.

Down here, the Powell field station measured 95 percent of average precipitation, Lovell was at 90 percent and Deaver was at 107 percent. Those measurements are for the end of March. Clark is at 116 percent, Fahey said.

When April’s measurements are in, those percentages could increase, Fahey said.

As of the end of March, the Powell area had 0.57 inches of precipitation this year, as opposed to 0.36 inches at the end of March 2010, according to Terry Foley’s Powell Weather at www.powellweather.net/index.htm.

Locally, with the ditch-burning season here, Fahey said people go online to get a weather and wind forecast at www.crh.noaa.gov/riw or call the Service at 800-211-1448, 24 hours per day.

“We’re always here,” Fahey said.

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