Summary appraisals of the nation's ground-water resources – Upper Colorado region

The Upper Colorado Region covers about 113,500 square miles (293,965 km²) in parts of Arizona, Colorado, New Mexico, Utah, and Wyoming. Drainage from about 97 percent of the region is to the Colorado River. About 60 percent of the land is owned or administered by the Federal Government, and another 15 percent is in Indian trust. The predominantly arid to semiarid region is sparsely populated (averaging about three persons per square mile, or about two and one-half persons per km²) and is used chiefly for grazing, recreation, and mineral development.

The water supply for the region comes from precipitation within the region, which averages about 95 million acre-feet (117,182.5 hm³) per year. Development of the region's water supply has been limited almost entirely to surface water. Only about 2 percent of the total estimated volume of water withdrawn (about 5.7 million acre-ft, or 7,030.9 hm³) and consumed (about 3.6 million acre-ft, or 4,440.6 hm³) in the region in 1970 came directly from ground-water sources.

By the year 2020 consumptive use of water within the region and water exports to adjacent regions are expected to total more than 6.5 million acre-feet (8,017.8 hm³) per year. Use of the ground-water resources of the Upper Colorado Region in water-resources management can help to meet these water needs.

A tremendous amount of water is stored in the rocks (ground-water reservoirs) of the Upper Colorado Region. Recoverable water in just the upper 100 feet (30.5 m) of saturated rocks is estimated to be as much as 115 million acre-feet (141,852.5 hm³). That amount is nearly four times the total active storage capacity of all surface-water reservoirs in the region. The average annual replenishable supply of the ground-water reservoir is about 4 million acre-feet (4,934 hm³). This amount of water could irrigate about 1.3 million acres (526,1,10 ha) of crops having an annual water requirement of 3 feet per acre (0.9 m/ha), or it could provide about 3,600 million gallons (13,627,440 m³) per day for industrial use.

Most of the ground water is in consolidated rocks, which generally yield water to wells slowly. Much of the ground water is saline and, in some places, occurs at great depths. Nevertheless, the ground water is more uniformly distributed than is surface water, both areally and with time; therefore, it can be used advantageously in overall waterresources management. Recent advancements in the field of demineralization and in evaluation and development of ground water make this possible.

Options available for use of ground water in water-resources management·in the·region include conjunctive use with surface water or development of ground water as an independent supply. The latter option could be for & perennial supply or for a time-limited supply (mining ground water), depending on the need and the existing ground-water conditions. All options can be carried out so as to meet the requirements of the Colorado River Compact. The options could be implemented to optimally develop the Upper Colorado River Basin's allocation of Colorado River water while meeting the Compact commitments to the Lower Basin.