WSP08430

• File Number: 8200.760
• Description: Yampa River General
• State: CO
• Basin: Yampa/White
• Water Division: 6
• Date: 1/1/3000
• Author: Unknown
• Title: Executive Summary - Task 4 Technical Memorandum on Hydrology Water Rights and Development of Basin Model - Yampa River Basin Alternatives Feasibility Study - Draft
• Water Supply Pro - Doc Type: Report/Study

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Description of Approach

Task 4 was divided into seven sub-tasks:

Sub-task 4a, Define Water Rights and Modeling Approach
Sub-task 4b, Review USFWS Hydrologic Model
Sub-task 4c Develop Site-specific Hydrology as Needed
Sub.task 4d, Develop Hydrologic Data Set
Sub.task 4e, Discuss Water Rights Transfer Issues
Sub-task 4[, Develop Basin Model
Sub-task 4g' Calibrate Basin Model

Sub-task 4a investigated the water rights structure of the Yampa River basin and compact
considerations. Information regarding the, water rigl:1ts structure of the basin was required in order to
evaluate the Juniper-Cross Mountain water rights, Certain aspects of the modeling approach also were
defined in this sub.task, including the handling of water right subordinations and the representation of
significant existing projects,

Sub-task 4b included a review of the USFWS HYDROSS model and the assumptions used in
development of the environmental baseline flow data. In order to adapt those baseline data for the
purposes of this investigation, it was necessary to understand the assumptions and modeling approach
used in their derivation. The treatment of-conditional water rights and existing projects which were
included in the USFWS environmental baseline were identified.

Sub-task 4c involved the development of site.specific hydrology, In order to carry out
operations studies of alternative reservoir development projects, it was necessary to estimate virgin or
baseline inflows at those sites as well as inflows and river gains elsewhere in the basin. These estimates
were based on regional analyses prepared specifically for the Yampa River basin.

The Yampa River Basin Model requires a baseline flow data set upon which operations of
proposed reservoirs and projects are overlain. In Sub. task 4d, the baseline hydrologic data set required
for modeling studies was developed using the results of Sub-tasks 4b and 4c.

The primary focus of Sub-task 4e was the analysis Juniper.Cross Mountain water rights with
emphasis on the potential for their transfer, subordination and use for instream flow purposes, potential
reservoir projects and prot'ection of junior absolute water rights. Existing subordinations of the Juniper-
Cross Mountain water rights were identifled along with the junior water rights which would be potential
beneficiaries.

In Sub-task 4f a basin hydrologic and water rights model was developed to assist in quantifying
the ability of existing supplies and reservoirs to meet projected water demands and to assess the effects
of reservoir operations on instream flows for endangered fishes. This model is capable of accepting files
of virgin or gaged inflows', simulating the allocation of these flows to various water rights and uses in the
basin, and predicting the resulting streamflow conditions in reaches of interest. in Sub-task 4g the basin
model was calibrated to insure proper performance in operations of reservoirs and maintenance of
hydrologic mass balance.

This Task 4 Technical Memorandum is a synthesis of our investigation of water rights issues in
the basin, compilation and development of complete hydrologic records and development and
calibration of the basin model.

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