Ten Tribes Partnership Tribal Water Study Colorado River Basin Ten Tribes Partnership Tribal Water Study Colorado River Water Users Association December 14, 2017

Tribal Water Study Builds on limited assessment of tribal water issues in Colorado River Basin Study Conducted jointly by Reclamation and the Ten Tribes Partnership Objectives Assess current and future water development for tribes of the Ten Tribes Partnership Assess system impacts resulting from development of tribal water, including to those relying on unused tribal water Identify tribal water development challenges and opportunities Study began in January 2014 2 2

Study Phases and Tasks – Status Phase 1: Current Tribal Water Use Assessment Phase 2: Future Tribal Water Development Assessment Phase 3: Assessment of System Impacts Phase 4: Identification & Evaluation of Opportunities & Challenges Phase 5: Final Report Production Identify system metrics Review and incorporate comments from Phase 1-4 draft report sections Develop data collection template Complete model (CRSS) enhancements Identify opportunities and challenges Select methods to estimate current use Determine modeling assumptions Select methods to project future development Develop draft report sections Combine into final Study Report Perform model simulations Meet with tribal reps to populate template Rank influencing factors and develop scenarios Complete reviews Synthesize and analyze results Catalog/analyze data Publish Study Report Develop draft report sections Conduct assessment of future development Develop list of CRSS enhancements Develop draft report sections Develop draft report sections Yellow denotes task is complete 3

Current Tribal Water Use Upper Colorado River Basin Lower Colorado River Basin 4

Potential Future Tribal Water Development Total Tribal Water Rights including Diversion Claims: 1,753,949 Acre-Feet per Year Upper Colorado River Basin Total Tribal Rights Including Diversion Claims: 952,190 Acre-Feet per Year Lower Colorado River Basin 5

System Effects Resulting from Development of Tribal Water Approach Findings Identify tribal water development scenarios Develop metrics to measure system effects Configure Colorado River Simulation System (CRSS) Develop modeling assumptions Analyze results Metrics more sensitive to future hydrology than tribal development Slight decrease in Lake Powell elevations and increase in Lower Basin shortage due to higher rates of tribal water development Assessment limited due to CRSS spatial representation 6

Challenges & Opportunities (potential future actions) Water Supply Challenges Agricultural Water Use Challenges Administrative and Legal Constraints Domestic, Commercial, Municipal, and Industrial Water Use Establishment of Continuous, Sustainable Funding Challenges & Opportunities (potential future actions) Environmental Challenges to the Use of Tribal Water Data Collection and Tools for Water Management Socioeconomic Considerations Diverse Geography of Tribal Reservations 7 7

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