8251

• UCREFRP Catalog Number: 8251
• Author: Rakowski, C. L. and J. C. Schmidt.
• Title: The Geomorphic Basis of Colorado Squawfish Nursery Habitat in the Green River Near Ouray, Utah.
• USFW Year: 1996.
• USFW - Doc Type: #93-1070,
• Copyright Material: NO

Draft Fmal Completion Report to UDWR for Contract #93-1070. Amendment 3

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determined by snorkeling. Determinations of habitat suitability were made from these measurements. The stream and

the accompanying physical parameters were then modeled for a variety of discharges. and areas of optimal, useable, and

unsuitable habitat were calculated for a range of low flows.

Hill and others (1991) used HEC-2 modeling to determine discharges for bankfull, riparian, and floodplain

flows. These modeled discharges were combined with historic exceedance probabilities for peak flows and flow

duration curves to determine the magnitude, duration. and hydrograph shape of different flow regimes (for example

riparian vs. valley flows). While Hill and others (1991) assumed that the restoration of a "natural" hydrogranh will

guarantee ecological integrity, they ignored many of the other consequences of stream alteration such as changes in

temperature, sediment load, availability and size distribution of sediment, and water quality.

A vailable Habitat Curves

Habitat availability curves were first developed for cold headwater streams in order to assess the impacts of

water diversions on standing crops of fish (Nestler. 1990). The US FIsh and Wildlife Service's IFIM and PHABSIM

(Bovee, 1982) have become widely accepted as standard methods to predict discharge-dependent changes in area of

available habitat. The model predicts weighted usable area (WUA) which is used as a surrogate for inslream physical

parameters th4tt are utilized by fish such as substrate, velocity, and water depth. The assumption is made that a

relationship exists between WUA and fish biomass. While validated for the cold headwater streams for which it was

developed (Nestler, 1990), IFIM and PHABSIM have been deemed inappropriate tools for evaluating relationships in

large warm rivers such as the Green River (Tyus, 1992).

To quantify changes in available habitat for the nursery habitat sections of the Green River, Pucherelli and

others (1990) used remotely-gathered data from five different discharges in 1987 to develop a correlation between

habitat availability and discharge for five alluvial reaches of the Green River including the Ouray NWR reach.

Pucherelli and others (1990) found the relationship between habitat availability and discharge at Ouray to be the weakest

of the 5 reaches, and that there was a bimodal peak in habitat availability at this site. Backwaters next to the bank

predominated over mid-channel backwaters, and there were more very large (> 1 000 m2) backwaters in the Ouray reach

than in the other sampled reaches. Stanford (1994) noted that the relationship developed by PuchereUi and others

(1990) for a single year's topography would only be valid for that year, and would likely change in subsequent years.

Habitat availability at base flow is a product of channel morphology, and within-channel morphology in this dynamic