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

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MEMORANDUM

TO: Dave Frick - Ayres Associates
FROM: Chuck Brendecke, Ed Armbruster - Hydrosphere
SUBJECT: Summary of Hydrosphere Model Runs to Evaluate Instream Flows
DATE: July 26, 1999

This memorandum summarizes assumptions and results of selected Yampa River Basin
model runs made by Hydrosphere during studies conducted between 1991 and 1996. The
summary focuses on the hydrologic implications of simulated water management strategies
to meet different instream flows at Juniper Canyon and Maybell. The principal assumptions
associated with each of these model scenarios, along with tables of resulting instream flows
and reservoir releases, are described below.

Definition of Scenarios

Numerous model scenarios were run using Hydrosphere's Yampa River Basin Model in
connection with Phase I and Phase II planning studies completed in 1993 and 1995,
respectively. Subsequent to the completion ofthe Phase II study, additional model scenarios
were developed to further examine a variety of operation and management options ("O&M
Studies"). Of the more than fifty model scenarios run over the course ofthese efforts, six are
described below. All these model scenarios simulated storage releases from an enlarged
Elkhead Reservoir. The six scenarios include:

. The Phase I Study scenario, which simulates an instream flow water right based on the
contemplated draft of the Juniper Project and having a priority date of 1954. Reservoir
storage releases are made to satisfy existing and future in-basin demands, some of which
are called out by the 1954 instream flow right.

. The Phase II Study scenario, which simulates flow targets based on Preliminary Flow
Recommendations developed in 1994. In-basin demands are assumed to divert free from
any call for instream flows. Reservoir storage releases are then made year around to
bring Maybell flows up to the level of the targets, if they are not met otherwise.

. The Flow Rec. - Junior scenario, which simulates flow targets based on Revised Flow
Recommendations made by the USFWS. Reservoir releases are made year around to
bring Maybell flows up to the target level.

-.,.
. The CWCB - Junior scenario, which simulates flow targets based on the now-withdrawn
CWCB instream flow filing. Reservoir releases are made year around to bring Maybell
flows up to the target level.

Appendix A

Hydrosphere Resource Consultants, 1002 Walnut Suite 200, Boulder, CO 80302

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