7922

• UCREFRP Catalog Number: 7922
• Author: Bovee, K. D.
• Title: A Guide To Stream Habitat Analysis Using The Instream Flow Incremental Methodology, Instream Flow Information Paper No. 12.
• USFW Year: 1982.
• USFW - Doc Type: \
• Copyright Material: NO

3. Incrementally changing one or more driving variables to reflect
a particular management alternative and determining total
habitat availability under the "new" system;
4. Determining alternative courses of action or remedial pro-
cedures to correct adverse impacts found in Step 3;
5. Repetition of Steps 3 and 4 to derive an array of effective
management or mitigation alternatives to minimize adverse
impacts; and
6. Evaluation of the alternatives to ensure that they meet manage-
ment objectives and that internal conflicts and trade-offs have
been resolved.
The sequence of analytical procedures varies considerably depending on
the initial condition of the system and the nature of the problem to be solved.
Therefore, completion of the six-step analysis can follow numerous pathways,
and because of this, a single approach cannot be used to address all problems.
The approach described in this report takes the format of a dichotomous key
which allows the flexibility to route the user through the appropriate pro-
cesses in the correct order.
A typical application of the IFIM will result in a large volume of output.
In order to be useful in the decision process, it is necessary to reduce the
volume while retaining the essence of the information. Several methods can be
used to prepare, display, and interpret the output. The goal of these activ-
ities should be to make a solution more obvious without requiring assumptions
that cannot be defended by the user.
The first step in this data reduction process is the computation of the
total habitat in each segment as a function of discharge. Total habitat for a
life stage is defined as the area of microhabitat per unit length of stream
times the length of stream having suitable water quality and temperature.
There are several ways of integrating total habitat, depending on the number
of microhabitat study sites and whether or not water quality or temperature
are suitable throughout the segment. Total habitat must be computed for the
entire range of discharges to be evaluated. The result is a single functional
relationship between total habitat and discharge for each life stage.
Habitat display and interpretation techniques include optimization,
habitat time series and duration curves, and stochastic or probabilistic
effective habitat time series. Optimization techniques are generally used for
instream flow recommendations and involve finding a flow for each month that
minimizes habitat reductions for all life stages and species occupying the
stream during the month. Habitat amounts can be weighted to reflect different
spatial requirements among life stages or different management priorities
among species.
A habitat time series is constructed by integrating the habitat-discharge
function with a time series of discharge. Habitat conditions without a project
are displayed using the existing habitat-discharge function and the historical
flow time series. Conditions with the project are simulated by developing a
habitat-discharge relationship reflecting the environmental changes caused by
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