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High runoff coming, but BuRec now downplays risk

May 22, 2014 - From staff reports

Snow runoff into Wind River and Bighorn Basin reservoirs still is predicted to be well above average for the rest of the spring into mid-summer, but a federal water manager doubts flooding will be significant this year.

The Bureau of Reclamation's most-recent forecast matches related predictions from other monitoring agencies.

BuRec forecasts runoff into the Wind River through July at 151 percent of the 30-year average. Predicted runoff is 600,000 acre feet of water, compared to an average of 397,000. An acre foot is a quantity of water covering an acre of ground to a depth of 1 foot. It equates to 325,851 gallons.

Runoff started slowly this year, with 569,000 acre feet of the 600,000 forecast still held in the mountains in May.

State figures

The statewide snowpack is 164 percent of average -- up from only 57 percent at this time last year, Lee Hackleman, water supply specialist with the federal Natural Resources Conservation Service in Casper, said in a statement Monday.

Hackleman said the last time Wyoming saw that level of snowpack at this time of year was in 2011. He said mountain snow is melting slower than normal this year.

Coleman Smith, manager of the Wyoming Area Office for the U.S. Bureau of Reclamation, said this year's anticipated high runoff will be a welcome relief to water managers.

"We don't have a lot of concerns about having too much water this year, like we did in 2010 and 2011," Smith said. "Mainly because our past two water years have been so poor, it's really depleted the reservoirs. So especially on the North Platte, we've got plenty of space for all the water we're forecasting to come down."

Water managers are removing water from reservoirs in drainages on the Wind River and Bighorn mountain ranges to make room for spring runoff, Smith said.

"The bottom line is we're not going to have a lot of flooding, which is of course what folks are worried about when they see high snowpack," Smith said.

Wind River downstream

Downstream at Bull Lake Reservoir west of Riverton, runoff into the lake is forecast at 165,000 acre feet, 120 percent of average. Only had 4,000 acre feet melted into Bull Lake by May 1.

At Boysen Reservoir north of Riverton, the runoff forecast is 140 percent of average at 750,000 acre feet. Average seasonal inflow is 534,000 acre feet.

Wind River system water under BuRec management eventually flow to Bighorn Lake just east of Lovell, also known as Yellowtail Reservoir. Inflow there is projected to be 183 percent of the 30-year average at 1.952 million acre feet.

Snow-water equivalent

Officials with the Wyoming Natural Resource Conservation Service offer similar data in their season-ending data. In the report compiled May 19, NCRS put the snow-water equivalent at 148 percent of median in the Wind River Basin. The previous week's figure was 135 percent, and the May 5 report showed 115 percent.

A year earlier in May 2013, the equivalent was just 45 percent of median.

Statewide, the snow-water equivalent stands at 164 percent, up from 152 percent a week earlier and far greater than the 57 percent measured statewide 12 months earlier.

Flood potential

And in its final flood potential outlook of the season, hydrologists with the National Weather Service again rated the flood risk in the Wind River Basin as "moderate to high," the second-highest level of risk measured by the office. The rating covers the area from Bull Lake Creek to the inlet to Boysen Reservoir.

Some high water already has been reported west of Riverton along the Wind River near Morton.

Only an area just west of Buffalo Bill Reservoir near Cody and a smaller zone near Tower Fall in Yellowstone National Park have are rated at higher flood potential than the Wind River Basin.

-- The Associated Press contributed to this story

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