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<br />01)1091 <br /> <br />. <br /> <br />. <br /> <br />Proposed Elkhead Dam and Reservoir Enlargement <br /> <br />Physical Facilities <br /> <br />The proposed project calls for raising the crest of Elkhead Dam 45 feet to elevation <br />6,420 MSL. This elevation was judged to be the maximum reasonable height the existing site <br />topography permits. This produces a normal full pool reservoir elevation of 6,406 feet and a <br />storage volume of approximately 44,900 af. <br /> <br />The enlarged Elkhead Dam would be constructed in a manner similar to the construction <br />of the original dam. The enlarged dam would be an earthfill structure, with the original dam <br />left in place to act as a portion of the new structure. The dam raise would proceed from the <br />downstream face, thereby not requiring full evacuation of the reservoir during the construction <br />process. <br /> <br />The existing spillway would be removed and replaced by a similar service spillway <br />immediately to its left. The new spillway would have a 100-foot long crest at elevation 6,406 <br />and would be capable of passing the 100-year flood. More infrequent floods would pass <br />through both the service spillway and the higher emergency spillway. <br /> <br />The existing primary outlet would either be removed or extended to the new spillway <br />chute. A new 6-foot diameter primary outlet would be constructed immediately to the right of <br />the new service spillway. An optional 2 MW hydroelectric power generation facility would be <br />positioned near the toe of the dam adjacent to the new spillway chute stilling basin. <br /> <br />A raise of the dam crest to elevation 6,420 MSL would permit an emergency spillway to <br />be cut through a saddle in the right abutment to an adjacent drainageway which joins Elkhead <br />Creek one mile downstream. The new emergency spillway would have a crest elevation of <br />6,409 feet. Features of the enlarged dam and existing dam are shown Figures 2 and3. <br /> <br />Reservoir Operations <br />Contract Storage <br /> <br />Additional storage capacity created by enlarging Elkhead Reservoir would be used to <br />directly serve existing and future demands and to make late season releases to augment <br />numerous junior water rights that might be called out by administration of the new Juniper- <br />based instream flow right. The instream flow right would likely be based on the contemplated <br />draft of the Juniper Project. Augmentation would occur by either direct water deliveries from <br />the reservoir or through various exchanges on the Yampa River upstream of Elkhead Creek. <br />Assuming that the existing ownership of the reservoir by Tri-State and the City of Craig is <br />maintained in the future, the size of the augmentation pool available for these purp6ses would <br />be 31,200 af. <br /> <br />In order to maximize recreational opportunities, an enlarged Elkhead Reservoir would <br />likely be operated to maintain seasonal recreation pools. Reservoir operation investigations <br />constrained maximum reservoir drawdowns to 10 feet and 20 feet during the summer and <br />winter months, respectively. <br /> <br />Recreational Uses <br /> <br />Future recreational use of an enlarged Elkhead Reservoir is expected to increase over <br />current conditions. This increase would be due to both an increase in regional population and <br /> <br />4 <br /> <br />FiLo.~,A <br />