WSP10841

• File Number: 8200.760
• Description: Yampa River General
• State: CO
• Basin: Yampa/White
• Water Division: 6
• Date: 1/1/1993
• Author: Hydroshpere
• Title: Yampa River Basin Alternatives Feasibility Study - Executive Summary - Draft - January 1993
• Water Supply Pro - Doc Type: Report/Study

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Executive Summary

Scenario III - Elkhead Enlargement . enlargement of Elkhead Reservoir
. Juniper rights converted to instream flow
. Juniper rights subordinated only to storage

Scenario IV - Stagecoach Enlargement . enlargement of Elkhead Reservoir
. enlargement of Stagecoach Reservoir
. Juniper rights converted to instream flow
. Juniper rights subordinated only to storage'

Scenario V - Williams Fork Project . enlargement of Elkhead Reservoir
. development of Williams Fork Project
. Juniper rights converted to instream flow
. Juniper rights subordinated only to storage

Potential reservoirs at the East Fork and Elk Creek sites were not explicitly modeled.
. Practically speaking, these two reservoirs are functionally equivalent to the Williams Fork and
Stagecoach Enlargement alternatives, which were modeled explicitly, in terms of water
deliveries and instream flow regimes in reaches of interest.

The "no action" scenario is functionally equivalent to simulation of the exercise of the
general subordination. This is true because the limits on the general subordination exceed the
estimated consumption under all existing and future junior demands represented in the basin
model. Thus, subordination of the Juniper rights in the model would make them the most
junior right represented, and unable to influence the operation of any other rights.

Results from model scenarios were used in two ways. First, the model was used to test
the sensitivity of predicted demands shortages, reservoir contents and instream flows to various
operational constraints, new storage facilities and instream flow requirements. Second, model
results for each scenario were compared against results of the baseline scenario in order to
evaluate which scenario could best meet basin wide water demands while maximizing
recreational opportunities and helping to protect historical flow regimes in reaches potentially
containing endangered fish habitat.

Evaluation Results

Scenario I - No Action (Baseline)

Scenario I of the Yampa River Basin Model represents physical conditions and water
rights as they currently exist and are administered in the basin. Three reservoirs were operated
in this scenario including Stagecoach Reservoir, Steamboat Lake and Elkhead Reservoir.
Operations of several other reservoirs presently existing in the basin, such as Lake Catamount,
Yamcolo Reservoir and numerous small reservoirs, were not explicitly modeled. Depletive
affects of these projects, however, were implicit in the gage based model hydrology or were
modeled as separate demands (this was the case with Lake Catamount).

Demands are met in the basin model according to assigned ranks; these ranks generally
correspond to the relative priorities of basin water rights. In all of the model scenarios, the
demand increment to reflect existing senior demands (potential 1989 conditions) were met prior
to allowing existing reservoirs to fill. While existing reservoir storage decrees are generally
junior rights, historically they have been allowed to fill without administrative call by senior
rights. Existing demands with rights junior to the Juniper rights were served after existing

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