WSP01154

• File Number: 8062
• Description: Federal Reserved Water Rights
• State: CO
• Basin: Statewide
• Date: 3/1/1995
• Author: USDOC
• Title: Instream Flow Incremental Methodology - A Primer for IFIM
• Water Supply Pro - Doc Type: Report/Study

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OulpUI 01 Microhabitat Model
(reaell specilic, Iile stage specific)

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Flow (dsl

Fig. 2.2. Flo\'....habitat relation developed by uSing
PHABSIM.

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versus now function showing how incremental
changes in flow result in quantifiable changes in
habitat value,
Even the best mid-range techniques leave the
analyst open to criticism, There are two fre-
quently challenged features ofPHABSIM, First is
the necessity for species suitability criteria (esti-
mated species responses to stream variables. nor-
malized onto a response cun'e), Figure 2.3 depicts
e%ample suitability criteria for two life stages of
brown trout, The curves show' that adults use
deeper and faster water than do juveniles. These
criteria may be established by several methods
ranging from solicitation of expert opinion to site-
specific collection and verification of field data
(Bovee 1986; Modde and Hardy 1992, (Thomas
and Bovee 1993), All of the criteria development
methods have been challenged to some degree,

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Brown Troul (Adult)

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Brown Trout (Juvenile)

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Velociry (Ips)

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THE INSTRt=;AM fLow INCREMEl\'TAL METHOLOOlOGY 13

The second criticism concerns the requirement to
analyze habitat species by species. which may not
account for habitat selection a!Tected by interspe-
cies competition (Ross 1986; Hearn 1987; Modde
et al. 19911. Note that the quality of habitat suit-
ability data, along with the signIficance of PHAB-
SIM's driving variables (e.g., depth, velocity, sub-
strate material, and cover), forms the basis for
most criticisms of this technique (Morhardt 19861,
To satisfy such criticisms, more in-depth analysis
is needed than is usually undertaken in simple
PHABSIM or HQI studies, PHABSIM is an incre,
mental method in the sense that it predicts
changes in habitat resulting from changes in flow,
but it focuses on onl)' a few variables affecting
localized fish behavior and ignores the dynamics
of habitat through time, The use of PHABSIM
alone also ignores many other biotic factors such
as inter- and intra-specific interactions.

Incremental Techniques

The mid-range techniques essentially provide
temporal snapshots of stream resources, When the
imperatives of negotiation or court proceedings re-
quire a more d)'namic look at the instream now
question, other techniques are needed. These pro.
ject bargaining problems have been labeled 'incre-
mental' <Trihey and Stalnaker 1985) because a
deep knowledge of how aquatic habitat value
changes as a functiOn of incremental changes in
streamt1.ow is required, This detailed quantifica-
tion must be developed to prepare for negotiations

.

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Fig. 2.3. Suitabilily-of-use Curves for
bro.....n trout.

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Channel index

12