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<br />To facilitate the computations involved in hydrologic and water rights data management, and
<br />to perform the reservoir operation analyses, a monthly hydrologic simulation model was used, It
<br />incorporated the Colorado water rights priority system and other legal and institutional
<br />arrangements identified during the Study, The modeling area covered the Upper Colorado River
<br />Basin above the Cameo gage near Palisade, This chapter describes the physical, legal and
<br />operational considerations incorporated in the model. Reservoir yields are described in the
<br />following chapter and alternative yields and costs of the Green Mountain Exchange Project
<br />components are described in Chapter 13,
<br />
<br />3,1
<br />
<br />HYDROLOGIC CHARACTERISTICS
<br />
<br />The Upper Colorado River watershed, which is the subject of this Study, extends from the
<br />Continental Divide at an elevation in excess of 10,000 feet, to the Cameo gage near Palisade, 210
<br />miles downstream, at an elevation of about 4,800 feet (see Figure 1,1), The drainage area above the
<br />Cameo gage is approximately 8,000 square miles,
<br />
<br />The major tributaries to the Colorado River in the study area are: the Fraser, Williams Fork,
<br />Blue, Piney, Eagle, and Roaring Fork Rivers, Smaller streams which also contribute to the Colorado
<br />River include Willow, Troublesome, Muddy, Rock, Divide, Elk, Rifle, Parachute, Roan, and Plateau
<br />Creeks, Principal reservoirs located in the Upper Colorado River Watershed include: Grand Lake.
<br />Shadow Mountain Lake, Lake Granby, Willow Creek Reservoir, and Green Mountain Reservoir, all
<br />operated by the USBR as part of the CBT; Williams Fork and Dillon Reservoirs owned by the DWB;
<br />Homestake Reservoir, jointly owned by the cities of Colorado Springs and Aurora; and Ruedi
<br />Reservoir operated by the USBR as part of the Fryingpan-Arkansas Project.
<br />
<br />Precipitation varies dramatically within the study area. At the higher elevations. precipitation
<br />exceeds 30 inches per year, whereas in Garfield County, 30 miles east of Grand Junction, Colorado,
<br />annual precipitation is as low as 10 inches per year, Snowfall in the study area begins as early as
<br />October and ends as late as the end of April.
<br />
<br />Average annual virgin flow of the Colorado River (based on 1951-1983 historical flows
<br />adjusted for major diversions and reservoirs as described in Chapter 4) ranges from about 0.5
<br />million af at the headwaters near Hot Sulphur Springs to 3,1 million af at the Cameo gage. A wide
<br />variation in total annual virgin flow is characteristic of the river as illustrated by annual extremes at
<br />the Cameo gage of 1.7 million af in 1977 and 5.2 million af in 1983,
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<br />3-2
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