It’s been another dry year for the Big Horn Basin, but it does appear the area will have enough water storage for the irrigation season.

The low amount of storage at Buffalo Bill Reservoir means that the Willwood Working Group 2, which has been studying means to manage sediment at the Willwood Dam, won’t be able to perform another flushing flow down the Shoshone River. Last year, the group conducted the operation as an experiment, and it showed promising results for sediment control operations at the dam.

David Waterstreet, program manager with the Wyoming Department of Environmental Quality, said the group  — which includes people from state and federal governments, as well as irrigation districts — consulted with the Bureau of Reclamation and made a group decision not to proceed with another such operation.

“Willwood Irrigation District is anticipating normal operations this year,” Waterstreet said. 

Two Bureau of Reclamation representatives — water scheduler Liz Cresto and deputy area manager Lyle Myler — gave an update on the situation at a March 15 meeting in Powell.

Myler is the interim area manager, holding the position after Carlie Ronca left the bureau. 

At the start of 2021, the reservoir was at 99% of average storage capacity, but by April 1, the snowpack was 90% of average. 

“After that April 1 timeframe, we really dried out,” Cresto said. 

The inflow volume into the reservoir from April until July was 75% of average, and 2021 ended with 90% of average for storage. From October through this month, total inflows were 74% of average, at 79,000 acre feet. 

With about 40 days remaining in the snow accumulation sequence for the year, the snowpack stood at 83% of median last week. This puts the Shoshone River Basin at the severe to extreme drought category, with 2 inches below normal snowpack. 

“The entire state is under some level of drought,” Cresto said. 

The current forecast for reservoir inflow is forecasted to be a total of 570,000 acre feet, with a minimum of 420,000 acre feet. If the season turns out wetter than expected, the reasonable forecast is 720,000 acre feet.

For comparison, the 30-year average is 740,000 acre feet of inflow. In 2021, the reservoir inflow was 548,000 acre feet. In 2020, it was 791,000 acre feet, and in 2019, it was 901,000 acre feet. 

The Buffalo Bill Reservoir’s expected elevation in June will be about 5,385 feet above sea level, which will drop to a little more than 5,360 feet by the end of the irrigation season. The reasonable minimum would see the reservoir go from about 5,370 feet above sea level to about 5,337 feet. In the event of a good year, it’ll go from nearly 5,390 feet to 5,368. 

Waterstreet said the working group will continue to consult with BOR forecasts to determine when the flushing flow operations can be conducted at the Willwood Dam. 

“It’s one operation that has been shown to be very successful” at moving sediment loads down river without seriously impacting aquatic life, Waterstreet said. 

The group has completed one contract it had with the U.S. Geological Survey to collect data on sediment loads at the dam. It’s currently evaluating a second contract, which will compile multiple studies on the sediment loads — including the USGS data already collected and studies by the University of Wyoming — to determine what sediment dynamics are occurring upstream of the dam. 

They will take all that research, Waterstreet said, to produce a scientific paper that should give a good understanding of how to best protect aquatic life downstream from the dam during operations.