9405

• UCREFRP Catalog Number: 9405
• Author: Pitlick, J. and M. Van Steeter.
• Title: Changes in Morphology and Endangered Fish Habitat of the Colorado River.
• USFW Year: 1994.
• USFW - Doc Type: Boulder.
• Copyright Material: NO

ABSTRACT
The present study investigates changes in channel morphology and potential losses of
fish habitat in reaches of the Colorado River near Grand Junction, Colorado. We have
used aerial photographs, discharge records, and field studies to evaluate the significance
of historical changes in flow regime and the effects of more recent flow events. Our
analysis of aerial photographs indicates there have been measurable decreases in the
amount of backwater habitat, although this vanes with the specific time period. A
preliminary analysis of peak flow data from several gaging stations in the region
indicates that in the last 30 years there has been a 19% decrease in the average peak
discharge of the Colorado River in the study area. This coincides with the time when
most of the major reservoirs in the upper basin were constructed. Peak flows on
unregulated tributary streams have remained stationary over the last 60 years. Field
studies conducted in 1993 during a period of higher than average runoff reveal minor
changes in channel morphology. Results from flow modeling are consistent with this
observation: model results indicate that the peak flow in 1993 was just sufficient to cause
significant movement of cobble and gravel bed material.
INTRODUCTION
There are currently four species of fish in the upper Colorado River which are listed as
endangered. These fish are the bonytail chub, the humpback chub, the Colorado squawfish, and
the razorback sucker. The latter two species were once plentiful in the reaches of the Colorado
River near Grand Junction, Colorado. Several factors appear to have contributed to the decline of
these fish, including competition with non-native species, deterioration in water quality, and a loss
of habitat due to river channelization and flow regulation. The present study focuses on the issue
of habitat loss. Biologists have suggested that backwaters are an important habitat for these fish
(Tyus and Karp, 1989), and that these habitats have been lost over time because of changes in the
flow regime of the Colorado River (Osmundson and Kaeding, 1991; Kaeding and Osmundson,
1989). It is reasonable to assume that a reduction in peak flows will result in changes in channel
morphology (Andrews, 1986; Williams and Wolman, 1984; Schumm, 1969), and thus, the U.S.
Fish and Wildlife Service has recommended that more water be released from upstream reservoirs
to improve in-channel habitat and enhance the recovery of these fish (Osmundson and Kaeding,
1991). However, it is not clear exactly how high these flows should be or how long they should
last. The present study was undertaken to detem- ine the extent of historical changes in riverine
habitat and to improve our understanding of the processes of habitat formation.