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I Introduction "Yampa Participants„ (a consortium of companies including Colorado-Ute Electric Association, Platte River Municipal Power Association, Salt River Agricultural Improvement and Power District, Tri-State Generation and Transmission Association, and Utah International). Ownership of all facilities and land, and operational responsibility was with the Colorado Division of Wildlife (CDOW). Basic physical characteristics of the dam/reservoir as originally constructed are presented in Table 1-1. The reservoir was developed with 8,310 acre-feet of standby cooling water storage for the Craig power plant and 5,390 acre-feet of recreation water storage of which approximately 3,000 acre-feet was below the outlet works as dead storage. Interim sedimentation has reduced this 13,700 acre-feet original storage volume to an estimated 13,000 acre-feet. In connection with the present study, the dam/reservoir dam plans and related reports were obtained from the CDOW and reviewed against the constructed conditions, as no official as-constructed plans are known to exist. The facilities appear to have been constructed essentially as designed and exist in a generally good physical condition less a normal amount of wear and tear. Construction records indicated only two events of notable significance which occurred during the original dam construction. The first was an instance of frozen soil in the embankment which was apparently resolved at the time it occurred. The second was excessive seepage at both the right and left abutment/embankment interfaces which required excavating, drilling and grouting. This seepage control program was judged successful. A minor, relatively stable clear flow is currently being experienced from the right abutment/embankment interface. Table 1-1 i i st cs Existing Elkhead Dam/Reservoir Character Inventory of Dams I.D. Number CO 00976 State of Colorado I.D. Number C-1 339A Elevations Crest 6,375 feet Service Spillway Crest/Normal Maximum W.S. 6,365 feet Primary Outlet, Intake Invert 6,333 feet Primary Outlet, Outlet Invert 6,316 feet Channel at Downstream End of Stilling Basin 6,295 feet Reservoir Capacity at Normal Maximum W.S. 13,700 acre-feet Spillway Capacity at Crest of Dam 16,000 cfs Primary Features/Dimensions 1,160-foot long homogeneous earthf ill embankment with chimney drain 315-foot long 36-inch RCP primary outlet pipe 135-foot arch shaped service spillway crest with a 40-foot wide spillway chute 40-foot wide USBR Type III Stilling Basin 20-foot wide county road on crest In addition to normal maintenance, repairs have been necessary over the years to the hydraulic lines, air vent and gate operators. There have been no major physical problems or any significant modifications to the facility with the exception of the addition of recreation features. Two items have been identified as needed modifications which should be accomplished when the dam is raised; the spillway sidewalls should be higher to avoid 1-5