76 CONSERVATION OF GROUND WATER 



is discharged each year from ground-water reservoirs by 

 nonbeneficial vegetation, mostly salt cedar, along the Gila 

 River below Coolidge Reservoir, the Salt River below 

 Phoenix, the Verde below Bartlett Dam, and the San Pedro 

 River. In addition, there are large losses by evaporation 

 from surface reservoirs on the Verde, Salt, and Gila Rivers. 



The outflow from the Gila Basin has been reduced to a 

 trickle by the greatly increased utilization of water within 

 the basin. In recent years there has been no surface outflow 

 except for a few days following heavy storms in the lower 

 part of the basin, and the underflow down the Gila channel 

 is considered to be only a few hundred acre-feet a year. The 

 inevitable result of this cessation of outflow has been the 

 accumulation of salts in the lower part of the basin — an 

 accumulation which has become noticeable in ground 

 waters near the Gila River channel for more than 150 miles 

 from the mouth. The use and reuse of water for irrigation 

 has contributed much of this salt to the lower valley by 

 dissolving soluble materials in the soil zone. But much of 

 the salt originates in saline springs within the basin or from 

 rocks such as the "salt banks" alongr the Salt River near 

 Chrysotile. For instance, the Clifton Springs contribute 

 about 4 acre-feet of water and 60 tons of salt daily to the 

 San Francisco River. Diluted by the Gila River, that water 

 becomes entirely suitable for irrigation, and the salt spring 

 thus gives a small advantage in quantity of water available 

 in Safford Valley. As the salt reaches the lower part of the 

 basin, though, it is a great detriment: each day's increment 

 of 60 tons is enough to make 40 acre-feet of fresh water un- 

 usable for irrigation. 



The proposed Central Arizona Project involves the impor- 

 tation of 1,200,000 acre-feet annually from the Colorado 

 River, a quantity considered to be sufficient to replace the 

 current overdraft on the ground-water reservoirs and to 

 permit the flushing of excess salt from the basin. Until this 

 water is available, the Gila Basin faces prospects of increas- 

 ing difficulties, some of which may be alleviated, however, 



