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2.1.1 Description of Physical Facilities <br />The following discussion provides a brief description of the physical facilities pertinent to the <br />West Slope operations of the CBT Project. <br />Alva B. Adams Tunnel (WDID 514634). The Adams Tunnel extends approximately 13 miles <br />under the Continental Divide and conveys Proj ect water from the Upper Colorado River drainage <br />to the South Platte River drainage. The tunnel diverts directly out of Grand Lake, a natural lake <br />located at the junction of Tonahutu Creek, North Inlet Creek and East Inlet Creek. The tunnel has <br />a rated capacity of about 550 cfs. Transmountain diversions through the tunnel are measured and <br />recorded at the east portal of the tunnel. <br />Shadow Mountain Dam and Reservoir (WDID 513695). This dam and reservoir serves as a <br />diversion structure to intercept the natural flows of the North Fork (mainstem) of the Upper <br />Colorado River for diversion through the Adams Tunnel. The reservoir commands a drainage <br />area of about 187 square miles. Shadow Mountain Reservoir is physically connected to Grand <br />Lake by an open channel and the water surface of the former is maintained at the same elevation <br />of Grand Lake and therefore provides additional forebay storage for diversions into the tunnel. <br />The reservoir also receives water pumped from the downstream storage in Granby Reservoir and <br />serves as a transfer reservoir for routing water into the tunnel. <br />The specified operation of Shadow Mountain Reservoir limits the fluctuation of the water <br />surface to one foot between the elevations of 8366 ft and 8367 ft above mean sea level <br />(incremental capacity = 1,839 acre-feet). The storage elevation is regulated by releases through <br />the tunnel and pumping from Granby Reservoir. It is not operated to provide regulation or <br />carryover storage. The water surface area at an elevation of 8367 ft is about 1,852 acres. <br />The 30-inch outlet works for Shadow Mountain Dam has a rated capacity of 100 cfs. Through <br />agreements with the U. S. Forest Service and the Colorado Division of Wildlife, releases are <br />made to ensure a minimum streamflow below the dam. The minimum release is normally 20 cfs <br />(January 1 through May 31); 50 cfs (June 1 through July 31); 40 cfs (August 1 through August <br />31); 35 cfs (September 1 through October 31) and 45 cfs (November 1 through December 31). <br />This release may be reduced if the inflow to the reservoir is less than these amounts. <br />Granby Reservoir (WDID 514620). This reservoir provides the majority of the Western Slope <br />regulatory storage for the project and collects water from the intervening drainages downstream <br />of Shadow Mountain Reservoir, including Arapahoe Creek, Cascade Creek, Stillwater Creek and <br />Willow Creek. The reservoir commands an incremental drainage area of about 124 square miles <br />(downstream of Shadow Mountain Dam). Water in Granby Reservoir is pumped up to Shadow <br />Mountain Reservoir, where it is conveyed to the Adams Tunnel for delivery to the Eastern Slope. <br />Granby Reservoir has a total capacity of about 539,758 acre-feet of which 74,190 acre-feet is <br />dead storage and 465,568 acre-feet is active storage. At this time, all of the active storage is <br />reserved for the sole purpose of supporting the transmountain diversions through the Adams <br />Tunnel. At its normal high water line elevation (Elev. 8280), the reservoir has a surface area of <br />about 7,260 acres. <br />Upper Colorado River Basin Informarion 2-3 <br />