Post-2026 Draft EIS Alternatives

Enhanced Coordination Alternative

This alternative is based on concepts from Basin Tribes, federal agencies, and other stakeholders to achieve protection of critical infrastructure while benefitting key resources (e.g., natural, hydropower and recreation) through an approach to distributing storage between Lake Powell and Lake Mead. Lake Powell releases would be determined based on a combination of Lake Powell and Lake Mead elevations, 10-year running-average hydrology, and Lower Basin deliveries. This alternative would include storage and delivery mechanisms for Lake Powell and Lake Mead and extensive flexibilities for all users. The operations incorporate Basin-wide shared contributions to the system, including Upper Basin conservation that would be stored in Lake Powell and Lower Basin shortages starting at 1.3 maf, approximately the average annual evaporative and system losses at and below Lake Mead, and reaching a maximum of 3.0 maf. Shortages would be triggered based on combined storage in Lake Powell and Lake Mead and distributed pro rata.

A curve of Lake Powell Eeffective and Lake Mead physical storage (% full) as a function of the Lower Basin CY Shortage (in million acre-feet) that provides the shortage guidelines to reduce deliveries from Lake Mead, under the Enhanced Coordination Alternative. A curve of target storage in Lake Powell (% full) as a function of target storage in Lake Mead (% full) that provides a coordinated operation guideline for Lake Powell and Lake Mead, under the Enhanced Coordination Alternative.

Shortage Guidelines to Reduce Deliveries from Lake Mead³

  • Shortages determined based on combined storage in Lake Powell and Lake Mead
  • Shortages begin at 60% full at a volume of 1.3 maf, then increase linearly, reaching a maximum of 3.0 maf at 30% full and below
  • Shortages distributed pro rata

Coordinated Reservoir Operations (Lake Powell and Lake Mead)

  • Lake Powell releases determined based on a combination of Lake Powell and Lake Mead elevations, 10-year running-average hydrology, and Lower Basin deliveries
  • Releases range from 10.8 to 4.7 maf

Storage and Delivery of Conserved System and Non-system Water (Lake Mead and/or Lake Powell)³

  • Storage up to 5.0 maf in Lake Mead with additional 2.0 maf Protection Pool; included for purposes of determining Lake Powell releases and shortages
  • Storage up to 2.0 maf in Lake Powell; included for purposes of determining Lake Powell releases but excluded from shortage determinations
  • Existing ICS converted to new mechanism immediately
  • Extensive flexibilities for all users: intra- and interstate transactions within each basin
  • Tribal water (both conserved consumptive use and unused) including in Lake Powell conservation pool and Lake Mead Protection Pool

Surplus Guidelines to Increase Deliveries/Releases from Lake Mead³

  • Surplus determinations limited to 70R (spill avoidance strategy) and Flood Control conditions

Additional Activities Above Lake Powell

  • Upper Basin conservation contributed to the Lake Powell conservation pool based on hydrologic conditions: up to 200 kaf per year for first 5 years, up to 275 kaf per year for second 5 years, up to 350 kaf starting in year 11

³ These operational elements contain modeling assumptions for water deliveries to Mexico. Shortage volumes include assumptions related to reductions in water deliveries to Mexico. Lake Mead storage volumes for the Storage and Delivery of Conserved System and Non-system Water include assumptions related to storage available to Mexico. Surplus Guidelines include assumptions related to increased deliveries to Mexico. Appendix A provides additional detail. Reclamation's modeling assumptions are not intended to constitute an interpretation or application of the 1944 Water Treaty or to represent current United States policy or a determination of future United States policy regarding deliveries to Mexico. The United States will conduct all necessary and appropriate discussions regarding the proposed federal action and implementation of the 1944 Water Treaty with Mexico through the IBWC in consultation with the Department of State.