7843

• UCREFRP Catalog Number: 7843
• Author: Stalnaker, C. B., et al.
• Title: The Instream Flow Incremental Methodology, A Primer for IFIM.
• USFW Year: 1995.
• USFW - Doc Type: Biological Report 29,
• Copyright Material: NO

12 BIOLOGICAL REpORT 29

Wetted Perimeter Method

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Discharge (cfs)

Bao 1991). Additional methods are described by
Wesche and Rechard (1980).

Multiple Attribute Standard-Setting
Methods

All of the methods previously discussed result in
a single stream flow value, recommended for a
defined period in individual streams. These meth-
ods have given rise to the term 'minimum flow.'
Such standard-setting recommendations are hard
to use in negotiation because too little information
is available to allow an informed compromise.
Much more must be done to answer the hard ques-
tions during negotiation (Wilds 1985). Answering
these hard questions requires moving away from
tools leading only to minimum flows. Techniques
need to show the relation between the amount of
habitat and stream flow. Such approaches allow the
analyst to display impacts on the resource of inter-
est for any given flow.
Tools that can be used to achieve this result fall
into two groups. The fIrst uses statistical analyses
to correlate environmental features of a stream
with fIsh population size. An example of this type
of analysis is Wyoming's Habitat Quality Index
(HQI), described by Binns (1982). An HQI is devel-
oped by regressing several habitat variables
against the standing crop of fIsh. This procedure is
stream-specific, and the recommendations are re-
lated to critical low flows. The second group of tools
link open channel hydraulics with known elements
of fish behavior. Examples include the Physical
Habitat Simulation System (PHABSIM), as first
presented by Bovee and Milhous (1978) and dis-
cussed again by Bovee (1982; also see Milhous et al.

Fig. 2.1. Use of the wetted perimeter
method to estimate instream flows.

1984). An important explicit element of PHABSIM
and HQI is an analysis of water supply. A water
supply analysis should accompany any standard-
setting technique to answer the question: What is
the likelihood that water will be available to meet
the standard?
Many people confuse IFIM with the Physical
HABitat SIMulation System (PHABSIM).
Whereas IFIM is a general problem-solving ap-
proach employing systems analysis techniques,
PHABSIM is a specific model designed to calculate
an index to the amount of microhabitat available
for different life stages at different flow levels.
Developed from techniques used in the Pacific
Northwest, PHABSIM requires the collection of
fIeld data on stream cross sections and habitat
features, hydraulic simulation to evaluate habitat
variables at different flows, and species suitability
criteria to calculate stream characteristics with
available habitat at alternate flows. Depending on
the complexity of the proposed project and the
complexity of the stream under study, the collec-
tion of fIeld data ranges from inexpensive and
quick to costly and time consuming.
Using PHABSIM enables the investigator to in-
form decision makers about the impacts on fIsh
habitat of different flows for different life stages.
Attention is typically given to the life stages of fIsh
species that are of special concern for management
or that are thought to be most sensitive to change.
The resulting relation between flow and habitat,
generated by linking species criteria with flow-de-
pendent stream channel characteristics, aids in
negotiation by more clearly depicting the effect that
less-than-optimum flow will have on habitat (Geer
1980). Figure 2.2 is an example ofa typical habitat