8249

• UCREFRP Catalog Number: 8249
• Author: Modde, T., W. J. Miller and R. Anderson.
• Title: Determination of Habitat Availability, Habitat Use, and Flow Needs of Endangered Fished in the Yampa River Between August and October.
• USFW Year: 1999.
• USFW - Doc Type: Project #CAP-9,
• Copyright Material: NO

the bottom, middle, and top portions of the upper riffle completed the habitat cluster. One of the three
cross sections on the upper riffle was located in the shallowest or widest part of the riffle.

Because depth, velocity, and wetted perimeter are more sensitive to flow changes in riffle habitats than
other habitat types, the analysis focused on riffles (per advice of the RIP selected expert panel).
Accordingly, during the extraordinarily high baseflows in 1997, priority was assigned to sampling riffles,
and in some clusters only the riffles were surveyed. Between one and three cross sections were
completed in the clusters where only riffles were sampled.

Data were collected at 25 to 30 points along each cross section. These data included habitat type and
substrate type (defined by Bisson et al. 1982 and Modde et al. 1991) depth and mean water velocity at
each point. Only one stage-discharge measurement was made at each cross section. The predictability of
only one stage-discharge measurement was tested by running multiple simulations and increasing the
Manning's n at low flow since roughness increases as flow decreases (Gordon et al. 1992). Increasing
Manning's n at flows of less than or equal to 40% and less of the measured flow did not change results
compared to using the calculated Manning's value.

Hydraulic Simulation
The conveyance channel module of the RHABSIM computer program (Payne 1995) was used to develop
the stage-discharge relationship for cross sections in the Yampa River. The model predicted changes in
channel variables at flows of 1, 10,20,40,60,80, 100, 125, 150,200,250, and 300 cfs by mesohabitat
type (run, riffle, and pool). Seven flow and/or channel variables were estimated by the hydraulic model
for each cross section by habitat type. The seven variables are defined as:
a) Wetted width: width of the stream at the water surface.
b) Percent wetted perimeter: The distance along the streambed in contact with the water divided
by the distance along the streambed between the grassline of each bank.
c) Depth: The vertical distance between the water surface and measured points on the
streambed.
d) Rise in stage: The difference in the vertical distance from the water surface elevation at a
flow of 1 cfs to the water surface elevation at a higher flow.
e) Width/depth ratio: A unit-less index of cross-sectional shape, where top width is divided by
average depth.
f) Cross Sectional Area: Wetted area in square feet determined by multiplying stream width by
average depth.

42