1. Yellowstone River Compact Commission Technical Committee Discussions Sheridan County Courthouse Sheridan, WY April 24, 2007 Bighorn Reservoir operations and long term management discussions RECLAMATION Managing Water in the West

2. Yellowtail Unit and Bighorn Canyon National Recreation Area Long-Term Issues Group

3. Draft Problem Statement “The amount, timing, and location of water available in the Big Horn River system to support all required and desired uses including, but not limited to, tribal obligations, recreation, aquatic organisms, power generation, and irrigation is limited and variable. Our challenge is to take a new look at all uses and needs, while recognizing commitments to authorized project purposes and other legal obligations—including water rights.”

4. Draft Group Charter “The Big Horn River System Long-Term Coordinating Group has been formed to identify, explore, and recommend alternative courses of action to the federal and state agencies responsible for managing Big Horn River and Big Horn Reservoir resources for their consideration as part of long-term management strategies.”

5. Yellowtail Unit Authorization: Flood Control Act of Dec. 22, 1944 (ch.665 Stat. 887) Senate Document 191—USACE/Reclamation plan for Missouri River Basin Development Project Purposes –Flood Control –Hydropower –Irrigation –Recreation –Fish & Wildlife –Sediment storage

6. Bighorn Canyon National Recreation Area Authorization: Public Law 89-664, October 15, 1966 Purpose “In order to provide for public outdoor recreation use and enjoyment of the proposed Yellowtail Reservoir and lands adjacent thereto in the States of Wyoming and Montana by the people of the United States….”

7. OPERATIONS - A BALANCING ACT AMONG THE AUTHORIZED PURPOSES OF THE YELLOWTAIL UNIT and the AUTHORIZED PURPOSES OF THE BIGHORN CANYON NATIONAL RECREATION AREA

8. Administration of the Yellowtail Unit and the Bighorn Canyon National Recreation Area Memorandum of Agreements between Reclamation and the Park Service: December 1964 (signed by the Secretary) Updated March 1972

9. 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 Flow levels for the River Fishery and water quality

10. Bighorn Lake Inflow Distribution Based on 1967-2006 Data Bighorn River Accretions less Depletions (Gain) 30% Buffalo Bill Release 28% Boysen Release 42% Annual Total

16. MULTIPURPOSE OBJECTIVES Elevations Targets Sept – Oct: A Desired Lake Elevation of 3635 provides space for late summer and fall rainstorms, recreation enhancement and wildlife habitat March: Position Lake Level between 3605 and 3615 to provide good fall and winter generation, prepare reservoir for spring runoff and provide desired fishery flows. This also increases probability of raising pool during Walleye Spawning July: Fill reservoir to normal full level of 3640 to provide good water supply for all water uses while leaving adequate space to control summer and fall rain events.

17. MULTIPURPOSE OBJECTIVES Desired River Operating Range 1,500 cfs – Approximate discharge to provide “firm” power generation as identified in DPR and provide minimum target flow for river fishery. Provide more then adequate water for downstream irrigation demands. Protects Reservoir storage in low runoff years except for the period of 2002 - 2004 4,500 cfs – Provides optimum power generation (allows full peaking) while providing more then adequate water conditions for river fishery and irrigation needs