Changing circumstances, public input and a bridge to new Colorado River operating guidelines

Changing Circumstances, Public Input And New Colorado River Operating Guidelines

What is an SEIS, anyway?
November 2, 2023


USBR Revised Draft Supplemental Environmental Impact StatementFor those who follow water issues in the Southwest – a cohort that is rapidly expanding to include “everybody” – the news in late October about the Bureau of Reclamation’s release of a new “draft management plan” for the Colorado River was hard to miss.

Reflecting some rare good news about river conditions, the story dominated environmental news coverage for nearly a week. For the first time in years, the focus was less on the immediate, precarious condition of the vital river system and more about the evolving long-term plan for managing the Colorado River sustainably.

As readers saw from most of the countless news reports on the new draft of a “Supplemental Environmental Impact Statement,” or draft SEIS, the recent good news has given river managers some breathing room.

near-record wet winter in the West and a proposal from the Lower Basin Colorado River states to conserve unprecedented volumes of water “reflects a shift away from short-term crisis management… [to] a more permanent rewrite of rules for how the river is shared,” as one report characterized the document.

AZ, CA, and NV Press ReleaseBut while the news reports are providing some welcome clarity about the potential consequences of this new, recently revised Draft SEIS, a question remains… what is it?

What is a “supplemental environmental impact statement” and how does it differ from a standard EIS? And as this most recent document is a “revised draft SEIS,” how is it different from the original draft released on April 14?

Much of the difference between the original draft and the current version is the result of what we have been seeing in the headlines: changing circumstances. Precipitation in the system’s Upper Basin last winter averaged 121 percent of average. That was big. But just as important is the enormous volume of public input to the conclusions of the draft SEIS garnered since April.

An EIS “is a government document that outlines the impact of a proposed project on its surrounding environment,” according to the American Bar Association. “Environmental impact statements are meant to inform the work and decisions of policymakers and community leaders.”

These are lengthy, complex documents that run hundreds of pages with often highly technical input from literally thousands of different sources in addition to their federal authors. To assist in understanding what an EIS (and its supplements), we have prepared the following primer.



Hoover and Glenn Canyon Dams

What is the purpose of a published SEIS of the Colorado River system?
Ultimately, the goal is to modify guidelines for operation of the Glen Canyon and Hoover Dams. However, this SEIS only covers actions through the end of the "Interim Period," which runs to the end of 2026.

Why do we need an SEIS?
Despite recent good hydrology in the Basin, the potential for continued low-runoff conditions that could lead Lake Powell and Lake Mead to decline to critically low elevations remains. Poor hydrology could impact operations through the remainder of the interim period prior to new guidelines being implemented January 1, 2027.

What does the SEIS focus on?
The SEIS focuses on:

  • New information
  • Changes in conditions since 2007
  • Impacts associated with the considered alternatives

The SEIS only analyzes the operations of Lakes Powell and Mead and does not consider operations of the Upper Basin reservoirs above Lake Powell. Again, this SEIS only covers actions through the end of the "Interim Period," which runs to the end of 2026.