8170

• UCREFRP Catalog Number: 8170
• Author: Trammell, M. A., K. D. Christopherson, C. L. Rakowski, J. C. Schmidt, K. S. Day, C. Crosby and T. E. Chart.
• Title: Flaming Gorge Studies
• USFW Year: 1999.
• USFW - Doc Type: Assessment of Colorado Pikeminnow Nursery Habitat in the Green River.
• Copyright Material: NO

Stanford [ 1994] stated that the Andrews and Nelson 1989 model was otentiall an a ro riate '
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addition to the Upper Colorado basin research program.
Flow Re mm '
co endataon Research
Historically, instream flow recommendations have been based on the flows necessary for '
maintaining a suitable amount of fish habitat during base flows [e.g., Tennant, 1975]. More
recent work suggests that a suite of flows is necessary to maintain ecological integrity offish '
habitat rather than just protecting the habitat at base flows [Hill et al., 1991 ]. This latter
approach is based on the assumption that habitat and nutrient availability for the fishes require
maintenance of the linkages between the stream and riparian, floodplain and upland areas. '
Two philosophies have shaped the design of instream flow for Colorado River native
fishes [Tyus, 1992]. The first philosophy is to provide minimum flows needed for species
survival during periods of low river discharge. These minimum flows do not ensure availability '
of optimal habitat, but seek to maintain and maximize the availability of existing habitat. The
second philosophy is to assist species recovery by increasing the availability of optimal habitats,
requiring that existing habitat be improved, and restoring "lost" habitats (i.e., habitats that are no
'
longer formed or available as a consequence of flow regulation). "Optimal" habitats under
regulated conditions include conditions of altered river hydrology and the presence of exotic

species, and are not the pristine river conditions that existed prior to regulation. For example, a '
habitat that was optimal prior to river regulation may no longer be optimal due to its use by
predatory species. For species recovery to occur in a system as altered, both physically and '
biologically, as the Green River, the second philosophy, with its emphasis on optimal habitats
and increased habitat availability, is the only viable option for species recovery.
'
Multiscale, Multiflow Studies
Ligon et al. [1995] noted the need for multiscale, interdisciplinary studies to quantify and
mitigate the downstream effects of dams. Hill et al. [1991] integrated several standard '
assessment methods into a methodology for determining the suite of flows necessary to maintain
ecological integrity and applied their methodology to the Salmon River at Whitebird, Idaho.
They noted the need for four flow components: base flows for fish, and channel-, riparian-, and
'
valley-process maintenance flows. Each of these flows inundated different ecosystems (e.g.,
stream channel and riparian ecosystem), and combinations of methodologies were necessary to

evaluate the appropriate flow regime for each component. '
Base Flows
Habitat availability curves were first developed for cold headwater streams to assess the '
effects of water diversions on standing crops offish [Nesler, 1990]. The US Fish and Wildlife
Service's Instream Flow Incremental Methodology (IF'IM) and Physical Habitat Simulation
system (PHABSIM) [Bovee, 1982] are widely used to predict discharge-dependent changes in '
area of available habitat. PHABSIM uses suitability curves determined from measurements of
physical parameters to model weighted usable area (WUA), a surrogate for the area of available
habitat for a target species. This model assumes that a positive, linear relationship exists ,
between WUA and fish biomass, which implies that the target fish population is habitat limited
[Mathur et al., 1985].
PHABSIM [Bovee
1982] was used b
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