Reclamation issues runoff forecast

Reclamation’s May forecasts of the April through July runoff predicted for the Bighorn River Basin are as follows:

Boysen Reservoir - Wind River April through July inflow to Boysen Reservoir is forecast at 700,000 af, which is 115% of the 30-year average of 611,000 af. Approximately 92,300 af of the forecast volume was accumulated during April, which is 182% of the April average. As of May 1, Boysen Reservoir was 68% full. *

Bighorn Lake - Bighorn River April through July inflow to Bighorn Lake is forecasted to be approximately 1,235,000 acre-feet (af).  Approximately 289,000 af of the forecast volume was accumulated during April, which is 163% of the April average. As of May 1, Bighorn Lake was 79% full.*

Buffalo Bill Reservoir - Shoshone River April through July inflow to Buffalo Bill Reservoir is forecast at 700,000 af, which is 94% of the 30-year average of 748,300 af. Approximately 36,000 af of the forecast volume was accumulated during April, which is 79% of the April average. As of May 1, Buffalo Bill was 63% full. *

Bull Lake Reservoir - April through July snowmelt runoff into Bull Lake Reservoir from Bull Lake Creek is expected to be 155,000 af, which is 108% of the 30-year average of 144,200 af. Approximately 4,900 af of the forecast volume was accumulated during April, which is 118% of the April average.  As of May 1, Bull Lake Reservoir was 52% full. *

*Reservoir is considered “full” when the pool elevation is at top of active conservation or joint-use pool.

The Bighorn Basin is a plateau region and intermontane basin, approximately 100 miles (160 km) wide, in north-central Wyoming. It is bounded by the Absaroka Range on the west, the Pryor Mountains on the north, the Bighorn Mountains on the east, and the Wind River and Granite Mountains on the south. It is drained to the north by tributaries of the Bighorn River, which enters the basin from the southwest, and passes through a gap between the Owl Creek and Bridger Mountains as the Wind River before changing its name to the Bighorn River at Wedding of the Waters, south of Thermopolis.

Reclamation’s storage reservoirs in the basin have a combined storage capacity of 2.6 million acre-feet and most of that capacity is attributed to Bull Lake, Boysen and Buffalo Bill Reservoirs in Wyoming and Bighorn Lake in Montana. Hydropower is produced at Boysen Powerplant and four powerplants supplied by Buffalo Bill Reservoir in Wyoming and at Yellowtail Powerplant in Montana.

For additional information on Buffalo Bill, Boysen, and Bull Lake Reservoirs, contact Wyoming Area Manager Lyle Myler at 307-261-5671. For additional information on Bighorn Lake (Yellowtail), contact Montana Area Manager Ryan Newman at 406-247-7298.