7245

• UCREFRP Catalog Number: 7245
• Author: Rose, K. L. and D. R. Hann.
• Title: Consolidated Instream Flow Report, Habitat Modeling on the Green River Using the Physical Habitat Simulation System.
• USFW Year: 1989.
• USFW - Doc Type: Grand Junction, Colorado.
• Copyright Material: NO

2. Study Site Selection

The PHABSIM methodology allows for two approaches to study site selection--
critical reach and representative reach (Trihey 1979). A critical reach is an
area that is extremely important for the continued survival of a species.
Determining a critical reach requires a rather extensive knowledge of the
stream hydrology and channel geometry in addition to species-specific life
history requirements. Given the limited knowledge of hydrologic and biologic
interactions controlling the fish populations, the critical reach approach was
considered inappropriate method upon which to select a site. A representative
reach on the other hand depicts the stream as a whole rather than
concentrating on one specific area. It is intended to incorporate all the
different variations which occur within the segment of the stream and
indicates the importance of hydrologic and geomorphic gradations within a
watershed for determining macrohabitat conditions. Study sites reported
herein were selected, and transects placed to "represent" habitats within
their respective sub-segments.

3. Field Measurements

Channel Qeometry and hydraulics

Field data collection in preparation for PHABSIM is based upon measurements of
certain parameters at multiple stream cross-sections according to techniques
described by Trihey and Wegner (1981). Site specific data essential for
su~cessful use of a hydraulic simulation model is obtained at a minimum of
four cross sections referenced to a common bench mark to characterize the
general cross-sectional shape and longitudinal streambed profile. The depths
and velocities measured at each cross section represent the average
characteristics of the stream hydraulics within an imaginary cell extending
half the distance to the next upstream and downstream transects and half the
distance to each adjacent vertical. Thus within each "cell" the water depth
and velocity are considered homogeneous. The number of verticals per transect
will vary depending on streambed configuration, width of the stream and
complexity of velocity distribution.

In general, after the transects, benchmark, and headstakes have been selected
and surveyed, a kevlar cable is strung from river left to river right and a
flat-bottom boat attached to the cable. A sounding weight is lowered from the
bow of the boat by a pulley system to obtain the water column depth and then
raised to 0.2 and 0.8 tenths of the total depth for velocity measurements. In
shallow areas, less than 2.5 feet, the velocity meter is attached to a top-set
wading rod to record velocities at 0.6 depth. The following sequence of
activities provides a general outline of the field activities and data
requirements of a PHABSIM study after the species and life stages of concern,
and study sites have been identified:

1. Identify cross sections, mark with headpins (rebar) and fenceposts.
These cross sections will represent differing hydraulic characteristics,
typical microhabitat conditions (i.e. pools, runs), and hydraulic
controls.

2. Survey a level line loop to determine relative headstake elevations.

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