WSP00615

• File Number: 8220.101.09
• Description: Glen Canyon Dam/Lake Powell
• State: AZ
• Basin: Colorado Mainstem
• Date: 10/25/1996
• Title: Record of Decision - Operation of Glen Canyon Dam Final Environmental Impact Statement
• Water Supply Pro - Doc Type: Record of Decision

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wilJ be responsible for recommending to Reclamation whether or not selective withdrawal should
be implemented at Glen Canyon Dam. Reclamation wilJ be responsible for design, NEP A
compliance, permits, construction, operation, and maintenance.

7. Emergency Exception Criteria: Operating criteria have been established to allow the
Western Area Power Administration to respond to various emergency situations in accordance
with their obligations to the North American Electric Reliability Council. This commitment also
provides for exceptions to a given alternative's operating criteria during search and rescue
situations, special studies and monitoring, dam and power plant maintenance, and spinning
reserves.

vn. BASIS FOR DECISION

The goal of selecting a preferred alternative was not to maximize benefits for the most resources,
but rather to find an alternative dam operating plan that would permit recovery and long-term
sustainability of downstream resources while limiting hydropower capability and flexibility only to
the extent necessary to achieve recovery and long-term sustainability.

Based on the impact analysis described in the final EIS, three of the alternatives are considered to
be environmentally preferable. They are: the Moderate Fluctuating Flow Alternative, the
Modified Low Fluctuating Flow Alternative, and the Seasonally Adjusted Steady Flow
Alternative. Modified Low Fluctuating Flow is selected for implementation because it satisfies
the critical needs for sediment resources and some of the habitat needs of native fish, benefits the
remaining resources, and allows for future hydropower flexibility, although there would be
moderate to potentially major adverse impacts on power operations and possible decreases in
long-term firm power marketing. Nearly all downstream resources are dependent to some extent
on the sediment resource. This alternative meets the critical requirements of the sediment
resource by restoring some of the pre-dam variability through floods and by providing a long-term
balance between the supply of sand from Grand Canyon tributaries and the sand-transport
capacity of the river. This, in turn, benefits the maintenance of habitat. The critical requirements
for native fish are met by pursuing a strategy of warming releases from Glen Canyon Dam,
enhancing the sediment resource, and substantially limiting the daily flow fluctuations.

The decision process for selecting the preferred alternative for the EIS followed a repetitive
sequence of comparisons of effects on downstream resources resulting from each alternative.
Alternatives resulting in unacceptable adverse effects on resources (such as long-term loss of
sandbars leading to the destruction of cultural resource sites and wildlife habitat) were eliminated
from further comparisons. Comparisons continued until existing data were no longer available to
support assumed benefits.

All resources were evaluated in terms of both positive and adverse effects from proposed
alternatives. Once it was determined that all alternatives would deliver at least 8.23 million acre
feet of water annually, water supply played a minor role in subsequent resource evaluations. (One
of the objectives of the "Criteria for Coordinated Long-Range Operation of Colorado River
Reservoirs" is a minimum annual release of 8.23 million acre feet of water from Glen Canyon