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" r ~ .- t; (' QU ,\.. d. powerplant will be awarded in January 1973, and will run about three years. Subsequent contracts will be required for comple- tion of the power facilities. 2. Crystal features.--Crystal Dam will be a double-curvature, thin-arch structure approximately 216 feet above the streambed with a crest length of 730 feet. The reservoir behind the dam will hold approximately 24,580 acre-feet of water, will have a shoreline of 20 miles, and 287 acres of water surface. a. Diversion tunnel.--The first contract, which should be awarded in December 1971, will include excavating the diversion tunnel through the right abutment and construct- ing four 5' x 8' tunnels for grouting and draining the dam foundation. The contractor will also have to construct access roads to the portals of the tunnel and disposal areas, and a temporary bridge across the Gunnison River. The tunnel will be 976 feet long, 12 feet in diameter, horseshoe-shaped, and concrete-lined. The tunnel location will be under the right abutment of the dam with the inlet portal approximately 500 feet upstream and the outlet portal 500 feet downstream from the dam axis. The method of excavation is expected to be a conventional drilling and blasting operation. Areas immediately upstream from the dam in the proposed reservoir basin have been designated for disposal of tunnel spoil. It is expected approximately 9,000 cubic yards of tunnel excavation and 38,000 cubic yards from portal excavation will be wasted in the reser- voir area. Aggregate sources for concrete lining consist of five approved commercial sources and a free-use area on Bureau of Land Management land. The tunnel contractor will have an option as to where to obtain the material and locate the processing operation, except that he may not obtain gravel from the Gunnison River in the vicinity of the dam- site. This will minimize activity in the river channel under this initial contract. There are approximately 3,lOO .cubic yards of concrete required to be placed in the tun- nel lining and structures. Presently there is no electrical power available at the bottom of the canyon. The contractor will be required to provide his own power, probably through use of portable diesel generators. b. Dam and powerplant.--The prime contract for the Crystal Dam structure will include construction of two cofferdams; one upstream of the dam to divert the Gunnison River into the previously constructed diversion tunnel and one 7