9326

• UCREFRP Catalog Number: 9326
• Author: U.S. Fish and Wildlife Service.
• Title: Draft Biological Opinion for Ute Water/Plateau Creek Pipeline Replacement Project, Mesa County, Colorado.
• USFW Year: 1996.
• USFW - Doc Type: Denver.
• Copyright Material: NO

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Some important habitats, such as inundated floodplain depressions used by
razorback suckers for spawning, are located outside the channel. Floodplain
depressions are principally derived from abandoned main channels,
side-channels, backwaters, and meander cutoffs.
The creation of complex channel habitat and the formation and eventual
abandonment of channel features from which floodplain depressions are formed
occur primarily during spring runoff when flows are of sufficient size and
duration to cause major changes in channel morphology through significant
erosion and deposition of bed and bank materials. The reduction in the
magnitude, duration, and frequency of high spring flows has slowed the rate at
which channel morphology changes. Consequently, the creation of complex
channel habitat and floodplain depressions has slowed. The placement of
riprap and other bank stabilization measures and the construction of dikes and
levees impede changes in channel morphology and contribute to the slowed
creation of complex channel habitat. In addition, the construction of dikes
and levees reduces existing channel habitat complexity by causing
channelization of the river. Dikes and levees also isolate existing
floodplain depressions from the channel during high flows. The slowed
creation of complex channel habitats and new floodplain depressions, the
reduction of existing channel habitat complexity, and the isolation of
existing floodplain depressions have acted to reduce the quantity and quality
of important habitat for endangered fishes.
Habitat Maintenance
Backwaters, used by various life stages of endangered fish, are damaged by the
deposition of fine sediments which reduces their depth and consequently their
duration and frequency of inundation. Gravel and cobble substrates, used by
squawfish for spawning, are damaged by the infiltration of fine sediments.
The establishment of vegetation on backwater sediments and on bars further
reduces the value of these habitats for endangered fishes. Furthermore,
higher flows are required to flush sediments from vegetated backwaters than
from unvegetated ones. Osmundson and Kaeding (1991) reported observations
that, on the 15-mile reach during the drought years of 1988 to 1990,
backwaters were filling in with silt and spring flows were not sufficient to
flush out the fine sediment. Also,- they reported that tamarisk colonized sand
and cobble bars. The lower frequency of high water years, therefore,
decreases the frequency at which silt and sand is flushed from backwaters,
fine sediments are flushed from gravel/cobble substrates, and vegetation is
scoured from backwaters and bars. As a result, the frequency at which these
habitats are suitable for use by endangered fishes has decreased.
~~ ~ Seasonal Habitat Availability
~ Summer (August-October): Osmundson et al. (1995) reported that availability
~ ~ of habitats did not differ significantly between periods of moderate flows and
• low flows. Though absolute area of habitat decreases with declining flows,
relative area or percent composition of habitat types changes little.
However, squawfish habitat use patterns did change. The fish used a greater
variety of habitats during moderate flows than during low flows. During
moderate flows, the fish used primarily back~:~tcrs, eddies, and pools. During