8188

• UCREFRP Catalog Number: 8188
• Author: Muth, R. T., et al.
• Title: Flow and Temperature Recommendations for Endangered Fishes in the Green River Downstream of Flaming Forge Dam.
• USFW Year: 2000.
• USFW - Doc Type: \
• Copyright Material: NO

Final Report

3-50

September 2000

and Labyrinth Canyons) or significant vertical accretion that has occurred in response to climatic
change (see Section 3.6.4). Very little floodplain habitat is available even at very high flows.

FLO Engineering Inc. (1996) modeled inundation of floodplain habitats in Canyonlands
National Park between RK 41 and 56 in Reach 3. Between 198 and 1,104 m3/s, little change in the
area of flooded habitat occurred. Between 1,104 and 1,500 m3/s, the amount of flooded habitat
increased from 2 to 200 ha(Figure 3.18). Another site in Reach 3 within Canyonlands National Park
was studied by C1uer and Hammack (1999). These authors used HEC-RAS (a numeric model
developed by the U.S. Army Corps of Engineers) to evaluate river-channel hydraulics for an 8-km
study site located between RK 61 and 69. They described the floodplain in this portion of Reach 3
as a series of high, fairly continuous levees with basins and channels between the levees. At flows
between 509 and 1,924 m3/s, the amount of inundated floodplain would increase linearly from about
3 to about 130 ha. If existing levees were removed, the amount of inundated floodplain would
increase linearly from 23 to 162 ha over this same range of flows.

Floodplain inundation in Reach 1 is not required to meet life-history needs (e.g., growth and
conditioning habitat of larval fish) of any of the endangered fishes. Neither razorback sucker,
Colorado pikeminnow, nor humpback chub are found upstream of or within Browns Park (where
most floodplain habitats exist in Reach 1), nor are they expected to be found there because the cold
temperatures of the water prevent their use of these areas. Consequently, floodplain inundation in
Reach 1 is not an objective of the flow recommendations in this report.

3.7 SUMMARY OF RELATIONSHIPS BETWEEN FLOW, IN-CHANNEL
HABITATS, AND FLOODPLAIN INUNDATION

Table 3.14 presents a summary of flow patterns and levels that, on the basis of our current
understanding of the Green River system, would produce suitable habitat conditions for endangered
fishes in the Green River downstream of Flaming Gorge Dam. The flows identified are those that
have been demonstrated or estimated to restore dynamic hydrologic and geomorphologic processes
that would maintain those habitats in areas designated as critical habitat or areas occupied by the
endangered fishes. These flows are not the same for all portions of the river because tributary inputs
and geologic changes along the river affect flow levels, seasonal patterns, channel hydraulics, bed
characteristics, and sediment loads. Consequently, separate flow values are presented for each of the
three reaches.

The availability and suitability of low-velocity backwater habitats during the base-flow
period depend on flow, but their relationship to flow patterns and levels will change from year to year
as a function of the elevation of sediment deposits behind which these habitats form. Because these
elevations are set by preceding high flows and then eroded by subsequent flows, it is not possible to
recommend a single flow that will optimize habitat area in all years. A specific recommendation for
a given year would have to consider antecedent conditions, characteristics of in-channel sediment,
and existing channel morphology.