PROBLEMS FROM DEVELOPMENT 37 



view of the likelihood of continually increasing requirements 

 for water, that similar shortages may develop in the humid 

 regions, but few areas in the eastern half of the country can 

 yet be included in this group. 



In some areas, a continuation of present rates of pumping 

 will eventually empty the groundwater reservoir; in others, 

 unusable water will be drawn into the reservoir as the eood 

 water is pumped out. In many areas, corrective measures have 

 been undertaken to bring the draft and replenishment into 

 balance. 



PERENNIAL OVERDRAFT AND EMPTYING RESERVOIRS. Several 



ground-water reservoirs in the arid Southwest are being drawn 

 upon at rates far greater than the average annual replenish- 

 ment. Of these, there are some in which it is not likely that 

 unusable water will be drawn in. The Santa Cruz Valley in 

 Arizona, Antelope Valley in California, and Mimbres Valley 

 in New Mexico are typical of areas with appreciable ground- 

 water replenishment but where current pumping is so great 

 that emptying of the reservoir is proceeding apace. 



Santa Cruz Valley of the Gila River Basin, Ariz. 1 About 

 one-third of all the water pumped from wells in Arizona 

 is withdrawn in the Santa Cruz Valley, which extends from 

 the international border at Nogales northward past Tucson 

 and thence northwestward to the Gila River. Heavy pump- 

 ing for irrigation started in 1914 in some places and has been 

 more or less continuous since, but the rate of development 

 has been accelerated since 1942. 



Total pumpage from the basin is computed to have been 

 about 420,000 acre-feet 2 in 1941, 730,000 in 1945, and 



i Reference: Turner, S. F., et al., "Ground-water Resources of the Santa Cruz 



Basin, Ariz.," U.S. Geol. Survey, Mimeo. repts., May 1943, 84 



pp.; March 1947, 45 pp. 



2 The common unit of water measurement in the West, and for irrigation 



generally, is the "acre-foot," which is equal to 325,851 gallons. In the East, and 



for municipal and industrial supplies generally, the common unit is "millions 



of gallons per day." To convert annual use, in thousands of acre-feet, to average 



daily use, in millions of gallons, multiply by a factor of 0.9. 



