The Bureau of Reclamation had predicted sufficient spring runoff to Buffalo Bill Reservoir for irrigation this year based on March 1 projections, but the April forecast may be less.

The new forecast was announced at a March 24 water meeting in Powell at the Eagles Lodge.

“It looks like we should have an adequate water supply this year,” said Mahonri Williams, Reclamation chief of resource management division in the Wyoming area office in Mills.

Based on a March 1 forecast and spring inflows to Buffalo Bill Reservoir, there should be enough water for the upcoming irrigation season and to provide end-of-season winter outflows of 350 cubic feet per second (cfs), Williams said.

That should be the case even if it is the minimum inflow projected March 1.

The bureau provides runoff projections based on estimates for three possible scenarios: minimum runoff, maximum runoff and average runoff, based on a 30-year average.

The March 1 minimum runoff projected for April through July was 550,000 acre feet, and the maximum expected runoff was 850,000 acre feet. The expected inflow was 700,000 acre feet, according to a table Williams provided.

An acre foot of water is the amount of water it takes to cover an acre of land with 1 foot of water.

The 30-year average from 1984 to 2013 is 677,800 acre feet.

The April through July inflow last year was 1,062,000 acre feet.

Williams said he expects the runoff forecast to change.

“When we update our forecast next week it will probably be a lower forecast,” Williams said Friday. “I expect it will go down, but I could not tell you how much.”

The final decision for the amount of winter outflow from Buffalo Bill Reservoir is decided at the end of September, which marks the end of the water year. Reclamation’s goal is to maintain around 449,100 acre feet in the reservoir. Storing more causes ice build-up where the South Fork of the Shoshone River flows into the reservoir, Williams said.

Buffalo Bill held 471,531 acre feet on March 26.

Snowpack has been tapering off recently.

“We were actually above average for a while, but coming into March, it quit snowing,” Williams said.

For example, on Feb. 16, the Shoshone basin’s snow water equivalent (SWE) was 115 percent of normal. By March 2, it was down to 108 percent of normal, and it had fallen to 89 percent on March 23, based on a 30-year average from 1981 to 2010 measured by the Natural Resources Conservation Service.

Above-average temperatures are expected from April through June in northwest Wyoming, according to a National Oceanic and Atmospheric Administration (NOAA) table provided by Williams.

Another NOAA table prediction during the same months said there were equal chances of above-normal, below-normal or average precipitation for the entire north half of the state.

“In other words,” Williams said, “they don’t know.”

The bureau plans to conduct a fresh prediction of the Buffalo Bill April-July inflow this week. “The spring precipitation is really going to tell the story of how much runoff we have coming,” Williams said.

Lee Hackleman, water supply specialist for the Natural Resources Conservation Service in Mills, was very succinct in his March 23 snow report comments, a report he updates every Monday: “Let it snow, let it snow!”

Accounts receivable

The Buffalo Bill Reservoir has water accounts specifying how much water different entities receive.

The state of Wyoming’s account is 189,965 acre feet. The Shoshone Project Account for area irrigation districts is 330,710 acre feet. The Polecat Bench account, for potential future development there, is 69,081 acre feet. All private accounts contain 15,061 acre feet.

An example of a private account user is the Shoshone Municipal Pipeline, which delivers potable water to customers around the Big Horn Basin.