C153642 Feasibility Study - Laserfiche WebLink

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Executive Summary 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-tenn project considers the enlargement of the existing Stagecoach Dam and Reservoir. The recommended long-tenn 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 elltent possible. The existing 800 kW (kilowatt) powerplant would be unchanged by the enlargement. Based on more detailed facilities plans and quantity takeoffs and on updated unit costs, the total development cost (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 rhake augmentation water releases to those juniors who would otherwise benefit from the subordination of the 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 excbange. Municipal and industrial (M&I) demands at Craig were assumed to have access to 1,668 af of existing storage dedicated to M&I 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 Elkheadenlargement. 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 S-25