38 CONSERVATION OF GROUND WATER 



1,250,000 acre-feet in 1949. These quantities are far larger 

 than the computed average annual replenishment to the 

 ground-water reservoir, which is derived chiefly by percola- 

 tion from the river and tributary washes and from irrigated 

 lands; there is little or no recharge directly from precipita- 

 tion on the valley. The average annual flow of the Santa 

 Cruz River at Nogales in the past 20 years has been about 

 15,000 acre-feet. The average replenishment of the ground- 

 water reservoir from all sources, as computed in 1942, is of 

 the order of 215,000 acre-feet. 



The evidence of overdraft and of progressive depletion 

 of storage in the ground-water reservoir is contained in the 

 records of water levels in wells. Progressive declines have 

 been noted in wells distributed throughout the basin, and 

 the declines have been most pronounced in areas of con- 

 centrated draft, particularly where there is little recharge. 

 As an outstanding example, water levels in the Eloy area 

 have dropped 50 feet on the average in the period 1940 to 

 1949. 



Pumpage has increased from about 275,000 acre-feet in 

 1945 to about 500,000 in 1949, when it was estimated to have 

 been about 20 times the recharge. The Eloy area was de- 

 clared a "critical area" by the state land commissioner in 

 1948, shortly after Arizona's ground-water law was passed, 

 and since then increased withdrawals have not been per- 

 mitted, whether from existing wells or new wells. However, 

 this regulation does not extend to other parts of the Santa 

 Cruz Valley from which the ground water in the Eloy criti- 

 cal area must be replenished, nor does it provide any means 

 for bringing the present pumping draft down toward the 

 estimated rate of natural replenishment. 



The Santa Cruz is one of the tributaries of the Gila 

 River, and the overdraft in the Santa Cruz Valley is just one 

 of many pressing problems that must be solved in working 

 toward full development of the "Central Arizona" area. As 

 an example of the complexity of the problem of full basin 

 development, the Santa Cruz Valley is bordered on the 



