9397

• UCREFRP Catalog Number: 9397
• Author: Hydrosphere Resource Consultants.
• Title: Gunnison River / Aspinall Unit Temperature Study - Phase I.
• USFW Year: 2002.
• USFW - Doc Type: 107,
• Copyright Material: NO

Gunnison River /Aspinall Unit Temperature Analysis -Phase I
Page 3
1.1 Statement of Need /Project Objective
The objective of this study is to determine the feasibility of increasing stream
temperatures in the Gunnison River at and below Delta, Colorado through structural and /
or operational modifications to the Aspinall Unit Reservoirs. The project is being
approached in a two-step process. The first phase of the work, which this report
summarizes, includes data collection and assessment; an overview of factors that may
constrain the Program's ability to meet temperature objectives; a preliminary analysis of
the data with the intent of gaining insight into the primary physical processes governing
water temperature in the basin; and modeling recommendations for the second phase of
the work.
The data assessment provided us with an understanding of the physical characteristics of
the study area. As part of the data assessment process, we attempted to identify any
previous modeling efforts in either the reservoirs or river reaches of interest.
The deliverables of this phase I study, which are reported in this document, are:
• Collection and assessment of existing data and models from the Gunnison Basin,
including stream and reservoir temperatures, mainstem and tributary inflows,
meteorological data, and any models of the reservoir /river system;
• A work plan outlining additional data collection and field work required to have a
"complete" database for future modeling efforts;
• An analysis ofnon-physical factors which may influence temperature control, such as
constraints on reservoir operations or water delivery obligations; and
• An initial assessment of the prospects for obtaining warmer stream temperatures at
Delta and what methods are likely to be most effective (e. g., modification of reservoir
release hydrograph vs. use of selective withdrawal for releasing wanner water).
Phase II of this project, if approved, would involve development and application of
numerical models of the Gunnison system. Results from these model outputs in phase II
would answer several questions, including:
• Would a TCD at Blue Mesa result in warmer release temperatures at Crystal?
• If so, how much warmer would they be?
• Would these warmer release temperatures translate into warmer river temperatures in
the area around Delta?
• What are the benefits of a fixed versus variable height withdrawal structure?
• How would a TCD impact the thermal structure of the Aspinall reservoirs?
Hydrosphere Resource Consultants