7752

• UCREFRP Catalog Number: 7752
• Author: Stanford, J. A.
• Title: Instream Flows to Assist the Recovery of Endangered Fishes of the Upper Colorado River Basin
• USFW Year: 1993.
• USFW - Doc Type: Review and Synthesis of Ecological Information, Issues, Methods and Rationale.
• Copyright Material: NO

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Society and the American Society of Civil Engineers set the stage for this endeavor to couple
management-oriented aquatic science with the physical mechanics of water flow in stream channels.
From the outset a fundamental tenet of the evolution of in stream flow methodology was that
something simpler (less mathematical) and more intuitive (to field personnel working for
management agencies) than full-blown ecosystem simulation was needed. As a consequence, the
methodology has tended to focus on economically important fishes and their habitat "preferences"
as determined by flow. This should not be surprising since a primary objective of wildlife and
fisheries management for decades has been to protect and enhance species-specific habitats in order
to maximize canying capacity, and hence, maximize harvest of surplus biota.
The first widely used methods were entirely based upon the fact that below some flow
threshold, physical habitat becomes limiting to fish and other stream biota during some part of their
life cycle. The most commonly used of these is the "Montana" method (rennant 1975 and various
modifications, see Wesche and Rechard 1980 for review) which attempts to relate perceived
problems, though rarely quantified (my observation, but also see Morhardt 1986), of the regulated
flows to the historical flow regime that occurred on the average. This approach to habitat
optimization, though still widely used (Reiser et al. 1989a), does not consider the importance of
flow variation and its complex relationship to channel geomorphology described above.

Statistical Approaches
Many studies have attempted, with widely varied success, to statistically relate some
measures of the biophysical attributes of rivers and streams to the disturbance effect of flow
variation. Most of these studies are basic science where the intent was to document aspects of the
structure and function of stream ecosystems with respect to flow changes. Much of the work was
focused on demonstration of relationships between the distribution, abundance and behavior of
aquatic biota and important physical variables using various regression and multivariate analyses in
natural (regulated situations compared to unregulated controls) and experimental designs
(experimental manipulations designed to simulate flow effects) (cf., Kroger 1973, Reice 1985,

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