| OCR Text |
Show PART II DESCRIPTION 2,800,000 acre-feet in 1962. Commencing in 1963 there began a withholding of large amounts of water in the upstream reservoirs of the Colorado River Storage Project. The average annual virgin flow at Lee Ferry, as unaffected by the activities of man, is estimated at 14.872 million acre-feet over the 52-year period 1914-65. As shown on the preceding map, the virgin contribution would average about 2.5 inches in depth over the basin. Water is presently (1965) exported from the region through some 39 transmountain canals and tunnels, mostly located at the headwaters of small tributaries. Several of these diversions have operated for many years and in 1965 the diversion totaled 513,000 acre-feet. There is one small diversion into the region from the East Fork Sevier River in southern Utah averaging 2,600 acre-feet per year. Prior to 1960 there were 92 storage reservoirs in the region having usable capacities of greater than 1,000 acre-feet and total usable capacity of 1,635,000 acre-feet. The large reservoirs built by the U. S. Bureau of Reclamation since 1960 are parts of the Upper Colorado River Storage Project and are mainly intended to store water for satisfying allocations to the Lower Colorado River basin while allowing additional local use of water from some of the headwater streams. Development of hydroelectric power is an added and most valuable benefit, which will in large measure repay the costs of the project. Recreation is another important benefit. However, loss to evaporation from increased exposed water surfaces is a deterrent to the construction of additional large reservoirs at the lower altitudes. Summary records of streamflow at 13 selected gaging stations and 41 of the transmountain diversions in the Upper Colorado Region for the period 1914-65 are listed on tables 1 and 2. Subregions The Upper Colorado Region has been divided for purposes of this study into three major hydrologic subregions, namely, the Green River Subregion, the Upper Main Stem Subregion, and the San Juan-Colorado Subregion. The Green River Subregion The Green River subregion drains an area of about 48,660 square miles in southwestern Wyoming, northwestern Colorado, and northeastern and east-central Utah. In addition to 44,744 square miles in the natural drainage of the Green River Basin, the subregion includes 3,916 square miles in the Great Divide Closed Basin. The Green River, the largest tributary of the Colorado River, rises in the Wind River |
