Supplemental Environmental Impact Statement for Near-term Colorado River Operations
The Bureau of Reclamation has released the revised draft Supplemental Environmental Impact Statement for Near-term Colorado River Operations. The supplement is to the December 2007 Record of Decision associated with the Colorado River Interim Guidelines for Lower Basin Shortages and Coordinated Operations for Lake Powell and Lake Mead, referred to as the 2007 Interim Guidelines.
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Key Updates to the Revised Draft SEIS
In the original draft SEIS issued April 14, 2023, Action Alternatives 1 and 2 were considered and fully analyzed along with the No Action Alternative. The analysis in the original draft SEIS was based on hydrology from September 2022. Since issuing the original draft SEIS, two key developments have occurred that require reassessment of the range of alternatives: improved hydrology and a proposal for a new alternative.
First, hydrology in the Colorado River Basin has improved compared with the hydrology at the time the SEIS analysis began in December 2022. Analysis in the original draft SEIS was based on hydrology from September 2022. Using the September 2022 hydrology, the percent of traces reaching critical elevations at Lake Powell (i.e., below 3,490 feet) through 2026 was 57%, and the percent of traces reaching critical elevations at Lake Mead (i.e., below 1,000 feet) was 52% without additional action. With improved hydrology from June 2023, the percent of traces declining below critical elevations is 8% at Lake Powell and 4% at Lake Mead through 2026.
Second, in May 2023, after the original draft SEIS was issued, the Lower Division States proposed an alternative for approximately 3 million acre-feet of water to be conserved to protect critical levels at Lake Mead ("Lower Division Proposal") (Lower Basin Plan Letter - May 22, 2023). The Upper Division States recommended that this proposed alternative be analyzed in the NEPA process (Seven States Letter - May 22, 2023). After the Lower Division Proposal was submitted, Reclamation temporarily withdrew the original draft SEIS so that it could fully analyze the effects of the proposal under the NEPA.
To assess the effects of these developments, Reclamation conducted modeling analysis of the No Action Alternative, Action Alternative 1, Action Alternative 2, and the Lower Division Proposal with updated hydrology from June 2023 and slightly modified assumptions, as described in Attachment B-1 to Appendix B of the revised draft SEIS. The results of that modeling analysis indicate that the risk of reaching critical elevations at Lake Powell and Lake Mead has been reduced substantially by hydrology.
Based on these modeling results, Reclamation will continue the SEIS process with detailed consideration of the No Action Alternative and the Lower Division Proposal. The Lower Division Proposal will be designated as the Proposed Action. Action Alternatives 1 and 2 will be addressed as alternatives considered but eliminated from detailed analysis.
Purpose and Need
The purpose of the SEIS is to supplement the 2007 Interim Guidelines to modify guidelines for operation of Glen Canyon Dam and Hoover Dam to address historic drought, historically low reservoirs, and low runoff conditions in the Colorado River Basin. The need for the modified operating guidelines is based on the potential that continued low runoff conditions in the Colorado River Basin could lead Lake Powell and Lake Mead to decline to critically low elevations, impacting operations through the remainder of the interim period (prior to January 1, 2027).
The revised draft SEIS analyzes two alternatives in detail:
- •The No Action Alternative, required by the National Environmental Policy Act, describes the continued implementation of existing agreements that control operations of Glen Canyon and Hoover Dams.
- • The Proposed Action ("Lower Division Proposal"), models changes to operations for both Glen Canyon Dam and Hoover Dam. The Proposed Action includes assumptions for a total of 3 maf of SEIS conservation through 2026 with a minimum of 1.5 million acre-feet physically conserved by the end of calendar year 2024. Under the Proposed Action, tier-based reductions and contributions shall be limited to the existing 2007 Interim Guidelines, Lower Basin DCP, and Minute 323.
For further information, contact the project team by email at CRinterimops@usbr.gov or call the project telephone line at (602) 609-6739.