8128

• UCREFRP Catalog Number: 8128
• Author: U.S. Bureau of Reclamation.
• Title: Operation of Glen Canyon Dam\
• USFW Year: 1995.
• Copyright Material: NO

Affected Resources
By analyzing public comments, the EIS team refined and evaluated issues of concern, identifying
the following resources to be evaluated: water, sediment, fish, vegetation, wildlife and habitat,
endangered and other special status species, cultural resources, air quality, recreation,
hydropower, and non-use value.
The canyon supports a complex system formed by interactions between communities of
organisms and their environment, or an ecosystem. Changes in a single process can affect
resources throughout the system. The EIS focuses on two processes that form linkages affected
by dam operations.
• Water release patterns directly or indirectly affect physical, biological, cultural,
recreational, and hydropower resources.
• Sediment transport and supply stabilizes archeological sites and camping beaches,
develops and maintains backwater habitats, transports nutrients, and provides a
foundation for vegetation that in turn provides wildlife habitat.
These two processes affect the complex, linked resources in the Colorado River corridor
downstream from the dam. For example:
Aquatic resources form a chain: river conditions created by the dam operations allow a
native alga, Cladophora glomerata, to flourish. This alga, in turn, provides habitat for
diatoms and for insect larvae and crustaceans that feed on diatoms. Together, these are
an important food source for non-native trout, native fish, and other organisms.
Habitat changes and non-native fish have created problems for native fish.
Terrestrial resources are linked together, as well as to aquatic resources. Water release
patterns and sediment affect riparian and emergent marsh vegetation which provide
habitat for wildlife.
Environmental Consequences
This EIS evaluates the alternatives' effects on both short-term needs of the environment and
long-term requirements to maintain and support the ecological elements of Grand Canyon.
These evaluations use indicators for each resource to measure the effects alternatives would have
on that resource.
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