WSP05634 - Laserfiche WebLink

Home Browse Search

. . . 0002;)0 CHAPTER V WATER RESOURCES development for any area would be desirable in order that all the water resources may be adequately considered. One objective of the investiga- tion should be to locate fracture zones in the bedrock where productive wells could be developed. A large-scale development of, the bedrock aquifers would involve a planned water-mining operation in which the life of the resource would be influenced by the extent of the annual withdrawal. The great depth of the more productive aquifers would affect the feasibility of mining since their dewatering would require a pump lift approaching 1,000 feet. Alluvial aquifers Deposits of alluvial and other unconsolidated materials occur as thin veneers in irregular patches throughout the San Juan Area. The more promising alluvial aquifers are found in outwash fans near the moun- tains and along stream flood plains. The only proven competent ground water reservoir in unconsolidated alluvium is in Spanish Valley. There is evidence that Castle Valley may also have deep, permeable valley fills. Spanish Valley is about 13 miles long and 1 to 2 miles wide. It is formed 'by the sandy-gravelly materials that fill the valley to depths of 80 to 300 feet. These materials were carried into Spanish Valley by flows of Pack and Mill Creeks. A detailed ground water investigation is being conducted in the valley by the Geological Survey which has pro- vided much of the information for this discussion. Approximately 212 wells have been developed in Spanish Valley, of which about 200 are in alluvium and 12 in bedrock aquifers. The annual withdrawal from both sources is about 4,800 acre-feet, of which 3,500 acre-feet is used for irrigation and 1,300 acre-feet for municipal purposes. Preliminary indications are that the recharge of ground water is about 20 second-feet or about 14,600 acre-feet annua~. The recharge consists of infiltration from Pack and Mill Creeks and from the irri- gation of valley land with water from these streams. Some recharge also results from precipitation on the valley floor. A significant water contribution to the valley fill from the underlying Navajo sandstone is also indicated by Geological Survey studies. Increased irrigation in Spanish Valley that would result from the potential Pack Creek Project described in Chapter IX would be expected to increase the ground water recharge. A large number of applications to appropriate ground water in Span- ish Valley have been filed with the Utah State Engineer who is withhold- ing action on them pending completion of the Geological Survey investiga- tion. These applications, together with some early filings already 51