7945

• UCREFRP Catalog Number: 7945
• Author: Bovee, K. D. and T. Cochnauer.
• Title: Development And Evaluation Of Weighted Criteria Probability-Of-Use Curves For Instream Flow Assessments
• USFW Year: 1977.
• USFW - Doc Type: Fisheries, Instream Flow Information Paper No. 3.
• Copyright Material: NO

THE USE OF COMBINATION PROBABILITIES
IN THE IFG INCREMENTAL METHODOLOGY
The IFG incremental methodology is rather unique among Instream
flow assessment procedures. At first glance, there appear to be few
common features among various riverine habitat alterations: stream
dewatering, flow augmentation, channelization, bank stabilization,
habitat improvement, or sedimentation. Each appears to be a unique
problem, requiring a unique solution. However, each of these problems
involves some alteration of river hydraulics, and the responses of
different species to those changes. Thus, it is possible to utilize a
standard methodological approach in the solution of these problems.
The Incremental Method was developed by personnel of the Coopera-
tive Instream Flow Service Group, U.S. Fish and Wildlife Service, Fort
Collins, Colorado. The IFG incremental method allows quantification of
the amount of potential habitat available for a species and life history
phase, in a given reach of stream, at different streamflow regimes,
with different channel configurations and slopes.
This method is composed of four components: (1) simulation of the
stream; (2) determination of the distribution of combinations of depths,
velocities, substrates, and cover objects, by area; (3) determination of
a composite probability of use for each combination of depth, velocity,
substrate, and cover (where applicable) found within the stream reach,
for each species and life history phase under investigation; and (4) the
calculation of a weighted usable area (roughly a habitat's carrying
capacity based on physical conditions alone) for each discharge, species,
and life history phase under investigation.
STREAM REACH SIMULATION
The purpose of a stream reach simulation is the determination of
the distribution of depths, velocities, and bottom types within the
channel at different levels of stream flow. Several hydraulic simula-
tion techniques are available, ranging in difficulty from taking many
current meter measurements at each discharge to be simulated, to sim-
ulating many discharges from one set of field measurements. A detailed
description of the theoretical and field measurement considerations will
be available under a separate title ("Theoretical Considerations, Data
Collection, and Cross-section Analysis for Assessing Hydraulic Changes in
Natural Stream Channels," IFIP 5, Cooperative Instream Flow Service
Group, U.S.F.W.S., Ft. Collins, CO - in preparation).
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