9596

• UCREFRP Catalog Number: 9596
• Author: Ayers Associates.
• Title: Yampa River Basin Research Final Synthesis Report.
• USFW Year: 1999.
• USFW - Doc Type: Fort Collins, CO.
• Copyright Material: NO

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

3.1.1. Tyus and Karp (1989)

The authors evaluated habitat use and streamflow needs of the Colorado pikeminnow, humpback
chub, bonytail and razorback sucker in the Yampa River based on a compilation of existing data,
both publish and unpublished. They examined the habitat requirements and factors limiting the
distribution and abundance of each species by life stage. Although they discussed year-round
flow needs in general terms, they did not quantify these flow needs. Major conclusions drawn
from this investigation are:

1. the Yampa and Green rivers constitute the most important riverine-system for the
maintenance and recovery of endangered fishes;

2. flows in the Yampa provide a natural shape to the hydrograph of both rivers, mitigating
the effects on native fishes due to flow regulation upstream on the Green;

3. high spring flows may inhibit invasion and proliferation of nonnative fishes;

4. Colorado pikeminnow and razorback suckers rely on habitats in both rivers to meet
various life stage requirements;

5. therefore, these two river basins should be considered as a single ecosystem when
determining the needs of the endangered fishes.

Each of the major components of the annual hydrograph plays a role in the life history of the
native fishes. Any significant modification of the hydrograph poses an obstacle to recovering the
endangered fishes. However, additional studies are needed to better quantify flow needs.

3.1.2. Harvey, Mussetter and Wick (1993)

Several spawning sites for the Colorado pikeminnow have been identified on cobble-gravel bars
in the lower Yampa Canyon. The authors examined the physical processes that create and
maintain these spawning bars during the 1991 and 1992 spring runoff seasons.

Pikeminnow begin migrating to these sites in May and early June and spawn on the recessional
limb of the spring hydrograph, when water temperatures typically are between 17 and 2rC.
Timing of spawning varies with the magnitude of flow, occurring earlier in low-water years and
later in high-water years. Pikeminnow require a clean gravel substrate on which to deposit their
eggs, as well as relatively quiet resting-staging areas in adjacent pools or shoreline eddies.

High spring peak flows are known to form and transform the major morphological features of the
river channel, including mid-channel cobble-gravel bars that provide spawning habitat for the
pikeminnow in Yampa Canyon. Sediments are entrained and conveyed by higher stream flows.
Velocity, rather than volume, is the critical factor that determines the capacity of the stream to
move sediment. Finer sediments (silts and sands) are more easily mobilized, while coarser
sediments (gravels and cobbles) require higher velocities to move them. Harvey et al. found that
as velocity increases on the ascending limb of the spring hydrograph, sediment is transported
from upstream sources to the vicinity of the spawning ITc!rs. The Little Snake River is a
significant source of this sediment. However, during the highest flows (19,500-27,500 cfs),
heterogeneous, poorly sorted sediments (silts to cobbles) are deposited in backwaters created by
sharp bends in the sandstone-embedded channel. These deposits are unsuitable for spawning.
As spring flows recede, finer sediments are scoured from the interstices of the coarser gravels
and cobbles to provide a suitable substrate for spawning. Thus, the entire springhydrograph is
necessary to transport, deposit, shape and clean spawning substrates for pikeminnow.

9