7886

• UCREFRP Catalog Number: 7886
• Author: Hydrosphere Resource Consultants.
• Title: Yampa River Basin Recommended Alternative, Detailed Feasibility Study
• USFW Year: 1995.
• USFW - Doc Type: Final Report.
• Copyright Material: NO

CHAPTER 2

RESERVOIR OPERATING STUDIES

This chapter describes the reservoir operating studies conducted as part of the present
study. These operating studies were accomplished using a computer model of the Yampa River
basin and were done in several phases as the study progressed. The discussion below first
presents an overview of these phases and then describes the basin computer model used to
perform the operations studies. A brief description of two phases of the earlier studies is then
presented. The chapter concludes with a detailed discussion of the final operating studies
which are also presented in the Preliminary Biological and Environmental Assessments.

OVERVIEW OF OPERATIONS STUDIES
The conclusions of the Phase I Study included a recommendation to move forward with
the conversion of a portion of the Juniper Project water rights to an instrearn flow water right
for the benefit of the endangered fishes and the present study began with this objective in mind.
The initial administrative and operational concept underlying this conversion was to make
releases from the enlarged Elkhead Reservoir to alleviate water supply shortages caused by the
"call" of the relatively senior Juniper-based instrearn flow right located at Juniper Canyon.
However, consideration of the existing subordination of the Juniper rights led to modification
of this concept to one of subordinating the instrearn flow right to upstream junior depletion and
then making augmentation releases from the enlarged Elkhead Reservoir to achieve the
instrearn flow levels that would have been realized in Juniper Canyon with an unubordinated
instrearn flow water right. From the standpoint of modeled physical hydrology these two
operations are indistinguishable, i.e., the amount of storage water released is the same in either
case.
However, it became evident as the study progressed that the terms of existing transfers
and subordination of the Juniper rights, along with concern related to protection of
Colorado's compact entitlements, may make it difficult to obtain and administer a subordinated
Juniper-based instrearn flow water right. Accordingly, the Colorado River Water Conservation
District ("River District") .and the Colorado Water Conservation Board ("CWCB") began
negotiation for a Memorandum of Understanding that contemplated the development of an
overall Yampa River Basin Water Management Plan. This water management plan would
include contractual agreements for intream flow enhancement from releases of stored water
and new instrearn flow water rights to protect natural flow and storage releases through the
river reaches of interest. Under the plan, comparable instrearn flow benefits could be realized
without the difficult conversion and administration of a Juniper-based instream flow right.
The operating studies conducted during the present study reflect this evolution in thinking
about how to best obtain and protect instrearn flows. Initial studies focused on quantification of
the contemplated draft of the Juniper rights and on the possible reservoir storage and operations
necessary to either mitigate shortages caused by the Juniper-based intream flow "call" or to
supplement flows obtained through a subordinated instrearn right. For comparison, another
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