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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000437

Executi"e Summary

modeled with a priority to fill ahead of the Juniper instream flow right. All basin demands had
access to water in the enlargement pool on a first-come, first-served basis.

Releases from the enlarged Elkhead Reservoir to satisfy demands were restricted by a
39,500 af minimum pool during the summer months, June, July and August. This feature of
the model was designed to reflect basin interests to maximize recreational potential of the
reservoir.

Scenario III model results revealed that shortages to existing senior demands were
unchanged in this scenario from the previous two scenarios. Shortages to existing junior
demand~ were substantially larger than in Scenario I but somewhat smaller than in Scenario II
because more storage water was available in Scenario III than in Scenario II. Existing junior
demands were shorted quite frequently, however.

Modeled shortages to the 2015 level demands were reiatively small but shortages at the
2040 demand level were large and frequent. Many of the shortages to future level demands
were located in the Craig area and were the result of deliveries out of Elkhead Reservoir being
limited by the 39,500 af summer re<;reation pool. Additional shortages continued to occur due
to constraints of the outlet works capacity at Elkhead and Stagecoach Reservoirs and due to
limitations on access by some demands to contract storage at Stagecoach Reservoir. .

Scenario IV - Enlargement of Elkhead and Stagecoach Reservoirs

Model runs in Scenario IV included both an enlarged Elkhead Reservoir and simulation
of an enlarged Stagecoach Reservoir. Elkhead reservoir was configured in exactly the same
way as in Scenario III. Stagecoach Reservoir was enlarged to a total capacity of 52,000 af.
This represented an increase in total storage of approximately 18,725 af over existing
conditions. The enlargement pool at Stagecoach was modeled in a manner similar to the
Elkhead enlargement in that the enlargement pool could be used by all demands on a first
come, first served basis.

Modeled shortages to existing senior demands remained unchanged from Scenario I, and
shortages to existing demands junior to 1954 were minor. Shortages to future level demands
were nearly eliminated by the .extra water supply available in the Stagecoach enlargement. The
fact that some shortages occurred to existing junior demands but not to future junior demands
in this scenario is a result of the inability of contract storage to serve certain future demands.

In Scenario IV ,all reservoirs remained nearly full throughout the study period, aside
from the seasonal operations of Stagecoach Reservoir and releases to supplement fish flows
from Steamboat Lake. The majority of the demands requiring storage releases were met out of
the Elkhead enlargement. There were no releases made to demands from contract storage in
Steamboat Lake. Augmentation releases from the enlargement pool in Stagecoach Reservoir
occurred only when the outlet capacity of Elkhead Reservoir constrained releases there.
Modeled shortages for Scenario IV are summarized in Table S-5.

Scenario V - Enlargement of Elkhead with Williams Fork Project

In Scenario V, a new storage project on the Williams Fork River was modeled along
with the Elkhead Reservoir enlargement. The Williams Fork Reservoir was modeled with a
70,000 aftotal capacity. Because the majority of basin demands are located above the
confluence of the Williams Fork with the Yampa River, Williams Fork Reservoir served
primarily as a source of exchange water. The exchange was used to satisfy downstream senior
water rights, I.e. the Maybell Canal and the proposed Juniper Canyon instream flow right, to

'.

S-16

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