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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000441

Executive Summary

saddle in the right abutment to an adjacent drainageway which joins Elkhead Creek one mile
downstream.

The Elkhead Dam raise would be accomplished on the downstream slope of the existing
dam. The upstream riprap slope would be extended to the new crest elevation at its current 3:1 .
. slope. Following preparation of the downstream slope, abutment and foundation, a 3: 1
downstream slope would be constructed. This would provide greater slope stability than the
existing 2.5:1 slope.

The recommended long-term project considers the enlargement of the existing
Stagecoach Dam and Reservoir. The recommended long-term project calls for the crest of the
dam to be raised 21.5 feet to elevation 7,231.5 feet by addition of roller-compacted concrete to . .
the downstream face. This elevation was judged to be the maximum reasonable height based
on topography, rock quality and preservation of existing dam features to the maximum extent
possible. The existing 800 KW powerplant would be unchanged by the enlargement.

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Based on more detailed facilities plans and quantity takeoffs, the total development costs
(including land and relocation and environmental mitigation) of the Elkhead Enlargement was
estimated to be $29.9 million. Construction costs alone were estimated to be $19.5 million.

Operating Procedures

General

For purposes of this Study it was assumed that existing reservoirs would continue to be
operated much as they have in the past. The primary exception would be the use of water in
enlargement pools at Elkhead and/or Stagecoach reservoirs. This study also assumed that
efforts will be made to establish and maintain fisheries in and downstream of the enlarged
reservoirs and that the enlarged reservoirs would be operated to maximize recreational usage
and minimize environmental impacts within the limits of water delivery requirements.

A primary function of the enlargement at Elkhead Reservoir would be to make
augmentation water releases to those juniors called out by the new Juniper-based instream flow
right at Juniper Canyon. These junior demands include those that would be served directly by
releases out of Elkhead and those that would be served through exchange. Municipal and
industrial (M&I) demands at Craig were assumed to have access to 1,668 af of existing storage
dedicated to M&1 use as well as to the enlargement. M&I demands at Hayden and Steamboat
were assumed to have access to contract storage in Stagecoach Reservoir but also to benefit
from the Elkhead Reservoir enlargement through exchange. All thermal-electric power
demands could be served, either indirectly or through exchange, by the Elkhead Reservoir
. enlargement pool after utilizing their existing contract storage supplies. Future Craig area
agricultural demands and the proposed coal gasification plant near Craig were assumed not to
have access to existing reservoir storage water but would be served from storage in the
enlargement pool at Elkhead Reservoir.

Reservoir operations in the long-term scenario were assumed to be identical to the near-
term. Water deliveries made out of the enlargement at Stagecoach would be similar to those
made from the Elkhead enlargement. All basin demands could be served by this water on a
first-come, first served basis.

Recreation pools were defined for both the Elkhead and Stagecoach enlargements. The
Elkhead Reservoir recreation pool was defined by a maximum drawdown of 10 feet during the
summer months. This corresponded to minimum storage of 35,000 af during June, July and

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