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

precaution to users until further data are collected and existing curves are
improved.

5. Hvdraulic Simulation

Knowledge of the magnitude and spatial distribution of point velocities is
often essential to biological analysis of riverine environments. The primary
purpose of incorporating incremental hydraulic simulation modeling into a
study is to make the most efficient use of limited field observations to
describe the occurrence of depths and velocities under a broad range of
unobserved streamflow conditions. The object of a hydraulic model is to
predict: 1) velocities at the selected verticals and the associated cells and
2) water surface elevations at the cross sections, from which depths at the
verticals may be determined by subtraction of the bed elevations. The
available substrate is then determined by the width of flow over the defined
substrate types.

In this analysis, the WSEI4S, water surface elevation stand alone program, is
used to predict the water surface elevations (WSE's) at each cross section at
flows of interest based on a regression of the WSE's and discharge
measurements collected throughout the summer. The accuracy of the hydraulic
simulations is evaluated by the ratio between discharge from the collected
field measurements and the discharge simulated by the model. This ratio should
range between 0.9 and 1.1 for an acceptable calibration. A ratio outside of
this will result in WSE predictions that are either too high or low. Using
the WSE's and discharge values from the WSEI4S program the IFG4 program can
pre~ict velocities. The accuracy of the velocity predictions is then
evaluated by the ratio between the measured and the predicted velocities.

The IFG4 program is typically used to predict stream velocities at 0.6 depth,
the mean column velocity. It can also be used to simulate velocities at other
depths, such as the nose velocity of the fish (Milhous et.al 1984). In this
analysis, it is assumed that Colorado squawfish and razorback suckers use
depths closer to the streambed than 0.6 depth and that a simulation of
velocities at 0.8 depth (0.2 depth above the streambed) might give a more
accurate indication of optimum flows. It must be noted, however, that the SI
curves were developed from velocity measurements taken at 0.6 depth and may
not be adequate for simulated velocities at 0.8 depth.

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6. Calculation of WeiQhted-Useable-Area (WUA)

Measurements of physical microhabitat, such as depth and velocity, were made
at intervals along each transect to describe the lateral distributions and
gradations of these parameters. Each stream cell was defined in the IFG4
program with a surface area (defined by the distances between transects and
verticals), a substrate type, and an average depth and velocity for various
streamflows. The HABTAT4 program was used in conjunction with this
information and the appropriate SI curve to develop a habitat index value,
termed weighted-useable-area (WUA), which represents the availability of
potential fish habitat as a function of discharge. The WUA value expresses
the potential of each cell within a stream reach to support a life stage of a
given species.

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