7906

• UCREFRP Catalog Number: 7906
• Author: Upper Colorado River Basin Instream Flow Team.
• Title: Green River, Determination of Flow Needs Using the Physical Habitat Simulation System ‎(PHABSIM)‎ in the Green River, Utah - Draft.
• USFW Year: 1988.
• USFW - Doc Type: \
• Copyright Material: NO

field season efforts and a recommended flow regime for the Green River
within this sec~rent .
II. PHYSICAL HABITAT SIMULATION METHODOLOGY (PHABSIM)
Methodology
The PHABSIM model is particularly well suited for displaying effects
of water allocation and proposed streamflow alterations on existing
riverine fishery habitat (Milhous et al. 1984). The effects are expressed
through changes of an index value called weighted-useable-area (W[iA}--
total surface area of the study area expressed as an equivalent surface
area of optimal fish habitat.
The model is based on the theory that changes in riverine habitat
conditions can be estimated on the basis of evaluating the behavioral
response of a species with respect to such streamflow dependant variables
as water depth, mean column velocity, and substrate. Thus it is intended
for use in situations where the flow regime and channel structure are the
major factors controlling the abundance and distribution of the fishery
resource and where field conditions are cor~atible with the assun~tions of
the methodology. These assumptions state that steady flow conditions
exist within a rigid channel and that fish species respond directly to
available hydraulic conditions.
Application of the methodology is comprised of several steps: 1)
determining the species distribution within the stream using literature
reviews, field observation, and consultation, 2) selecting a study reach
using either a critical reach or representative reach approach, 3)
measuring biologic and hydraulic characteristics in the reach using a
multiple transect approach, 4) determining species preference or use of
2