7738 ‎(2)‎

• UCREFRP Catalog Number: 7738
• Author: Ruppert, J. B., R. T. Muth and T. P. Nesler
• Title: Predation on Fish Larvae by Adult Red Shiner, Yampa and Green Rivers, Colorado
• USFW Year: 1993
• USFW - Doc Type: The Southwestern Naturalist
• Copyright Material: NO

1
Executive Summary

Project contemplated draft, as converted to an instream flow right at Juniper Canyon, was
' evaluated to characterize the impact on the annual hydrograph of the Yampa River.
The modeled influence of the Juniper instream flow right was to slightly modify the
annual temporal distributions of flow on the Yampa River. The instream flow right had the
' effect of slightly increasing flows during the low flow fall and early winter months.
Augmentation releases for junior demands which were called out by the instream flow right (in
scenarios II through V) asserted an increased draw on basin reservoirs, which resulted in a
slight decrease in Juniper Canyon flows in the spring and early summer months when the
1 reservoirs filled.
Instream flow targets were modeled in two other locations on the Yampa River besides
' Juniper Canyon. These instream targets were located immediately below Stagecoach Reservoir
and below the City of Craig. The Stagecoach target reflects current operating procedures of
the reservoir. The instream flow target (a constraint really) below Craig was modeled only in
Scenario V to help protect this river reach from the depletive effects of operating an exchange
' out of Williams Fork Reservoir. No instream flow targets were modeled below Elkhead
Reservoir, Steamboat Lake or the Williams Fork Reservoir.
' Model results from Scenarios I through V indicated relatively little variation between
development scenarios all through V) with respect to instream flows in Juniper Canyon and
other mainstem reaches. Selection of the recommended development alternative was not
' possible based on instream flow considerations alone.
7

Reservoir Fluctuations
The degree to which reservoir levels fluctuate has important biological and recreational
implications. The ability of a reservoir to act as a water supply for perimeter wetlands
depends greatly on seasonal rises and declines in the water surface elevation. In addition,
reservoir fish populations can be affected by the degree and frequency of reservoir operations.
There were relatively minor differences in reservoir fluctuations between the modeled
scenarios. Hence, as with the evaluation of instream flow predictions, it was not possible to
select the best water development project in the Yampa Basin based solely on the effects of
operations of reservoirs on fisheries and wetlands. Development of new reservoirs would
generally have more impact to existing wetlands than reservoir enlargements.
Project Costs
Preliminary cost estimates were generated for development of storage capacity at all five
candidate reservoir sites, although only the Elkhead and Stagecoach enlargements and the
Williams Fork project were modeled in the operating studies. These preliminary cost estimates
were intended to provide only com„_parative information between alternative projects. A greater
amount of information on physical characteristics was available for the Stagecoach and Elkhead
sites than the other sites. To allow comparison of projects on an equal basis, several
simplifying assumptions were applied to normalize cost estimating parameters. All estimated
costs reference the Engineering News Record Cost Construction Index No. 4777 (January,
1991). These figures were not intended to represent discrete, absolute numbers.
The preliminary cost estimate for the enlargement of Elkhead Reservoir was based on a
new reservoir with a total capacity 52,000 af; total costs of this dam raise and associated work
were estimated to be in the range of $15 - $20 million. The maximum reasonable reservoir
enlargement size at the existing Stagecoach Reservoir is 52,000 of and the preliminary costs of
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