Yellowtail Dam & Bighorn Lake Billings , Montana January 2011

1. RECLAMATION Managing Water in the West Yellowtail Dam & Bighorn Lake Billings, Montana January 2011

2. Operating Requirements & Objectives • Mandatory /Legal • Recognize all senior downstream water rights • Fulfill compact obligation with Native American Tribes • Meet contract commitments for stored water • Dam safety • Operating Objectives • Maximize power generation benefit • Maintain storage space for flood control • Maintain desired lake levels for recreation, reservoir fishery and waterfowl • Maintain desired river flows for the river fishery and water quality

3. Multipurpose Benefits • Water Rights • Regulate stream flow and release water for irrigation • Compact Commitments with N. Cheyenne and Crow tribes • Industrial water supply • 6,000 AF contract with PPL- MT • Flood control • Flood protection Benefits= $113 million since construction (2007) • Hydropower • 260 MW powerplant (8,000 cfs) • Peaking power supplied to two grid systems • Average Annual generation = 866.0 million kwhrs (1967-2007) • Average Annual power sales @ .023/kwhr = $20 million per year • Montana and Wyoming both benefit from power generated • Fish & Wildlife • Lake fishery, river fishery, and waterfowl • Recreation • Bighorn Canyon Recreation Area and Bighorn River • Water Quality • Reduce high levels of nitrogen supersaturation • Sediment retention

4. BIGHORN LAKE STORAGE ALLOCATIONS Dam Crest Maximum Water Surface or Top of Surcharge Elev. 3660.00 (1,381,189 Acre-Feet) Elev. 3660.0 SURCHARGE - 52,829 Acre-Feet Top of Exclusive Flood Elev. 3657.00 (1,328,360 AF) EXCLUSIVE FLOOD CONTROL - 258,331 Acre-Feet Top of Joint Use Elev. 3640.00 (1,070,029 Acre-Feet) JOINT USE - 240,342 Acre-Feet Top of Active Conservation Elev. 3614.00 (829,687 Acre-Feet) Spillway crest Elev. 3593.00 ACTIVE CONSERVATION - 336,103 Acre-Feet FISH WILDLIFE RECREATION AGRICULTURE POWER MUNICIPAL INDUSTRIAL Top of Inactive Elev. 3547.00 (493,584 Acre-Feet) Powerplant Penstock Elev. 3450.00 INACTIVE CONSERVATION - 477,576 Acre-Feet Irrigation Outlet Elev. 3400.00 River Outlet Elev. 3300.0 Top of Dead Elev. 3296.50 (16,008 Acre-Feet) DEAD - 16,008 Acre-Feet Streambed Elev. 3166.0

5. Operational GoalsPrior to Review • Desired lake elevations requested by lake interests • Minimum desired lake elevation recommended by the NPS for the summer recreation season - 3617. • Minimum late fall lake elevation recommended by the Wyoming Game and Fish to provide suitable waterfowl habitat - 3635. • Draft reservoir to 3630 to prevent ice-jams from forming in low end of Shoshone River • Maximum lake elevation recommended by the NPS for the summer recreation season to protect facilities - 3642. • A rising reservoir level through the spring for walleye spawning.

6. Operational Goals (continued) • Desired river flows requested by Montana FW&P by letter dated November 19, 1986 • 2,500 cfs – to provide good spawning, rearing and cover conditions in all major side channels. • 2,000 cfs - to provide adequate spawning and rearing conditions in most side channels but cover for adult fish is limited. • 1,500 cfs – to provide only main channel habitat and no side channel habitat • Minimum release included in the 1962 Definite Planning Report for the Yellowtail Unit – 1,000 cfs

7. Operational Goals (continued) • Power generation • Utilize available water supply to maximize generation at time of greatest demand • Maximize reservoir head to provide the greatest generation per unit of water • Flood control • Coordinate operations with the Corps of Engineers to provide system benefits • Draft water from the Joint-Use pool based on mountain snowpack forecast to provide space for expected runoff while allowing the reservoir to fill to the top of the joint-use pool by end of July. • Operate the Exclusive flood pool as directed by the Corps of Engineers to control rain flood events and high snowmelt runoff.

8. QUESTIONS & COMMENTS