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

macrohabitat characteristics such as water quality or temperature. Micro-
habitat characteristics are measured at other study sites. The basic habitat
accounting unit is the river segment, a relatively long reach of stream
exhibiting homogeneity in channel characteristics and flow regime. Guidelines
for establishing segment boundaries include places where the average base flow
changes by 10 to 15%, or where changes in slope, channel dimensions, or channel
pattern are apparent.
A river segment may contain one or more study sites for macrohabitat
and/or microhabitat measurements. A single study site is used to describe one
or the other type of habitat, but generally not both. Macrohabitat study
sites include control sites, point sources, and a network of stations to
define concentration or temperature profiles along the stream. Control sites
are used to determine the background concentrations or temperatures above the
influence of chemical or thermal inputs. Point sources include outfalls of
pollutants, runoff points for aggregated nonpoint sources, and confluences of
tributaries. Many biologically important water quality constituents change
concentration through chemical and biochemical reactions as they move down-
stream. A network of monitoring stations, often evenly spaced along the
stream, is used to define such concentration or temperature profiles.
Several types of study sites are utilized for the measurement of micro-
habitat characteristics. Representative reaches are selected through a random
or uniform sampling process, and are used to describe the typical microhabitat
in a segment. Several representative reaches may be needed in segments
exhibiting gradual longitudinal changes in slope, channel dimensions, or
channel pattern. Critical reaches are generally atypical of the microhabitat
in a segment. The two criteria used to define a critical reach are:
1. The microhabitat characteristics of the critical reach are
controlling or limiting to the evaluation species (such as
limiting migration or spawning); and
2. These microhabitat characteristics are unavailable or in short
supply in the representative reaches.
A special type of critical reach is termed a unique reach. Unique reaches
apply only to endangered species, and are typified by large concentrations of
these species in streams where such concentrations are unusual. The reasons
for the concentration of an endangered species are usually unknown, but a
unique reach can be designated by virtue of the status of the evaluation
species.
The analytical sequence followed in an application of the IFIM consists
of six steps:
1. Describing the river or system in its present state;
2. Determining the mathematical expressions and functional rela-
tionships describing the temporal macro- and microhabitat
availability of the present system and integrating to determine
total habitat availability;
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