PROBLEMS FROM DEVELOPMENT 75 



tions, released in July, 1950, shows the magnitude and com- 

 plexity of the hydrologic problems in the valley. 



Gila River Basin, Ariz. 23 The Gila River Basin includes 

 about half the area of Arizona and more than 90 per cent 

 of the population, industry, and irrigated land. The basin 

 includes several individual ground-water reservoirs, of 

 which Safford Valley, Santa Cruz Valley, and the Wellton- 

 Mohawk area are described separately. The problems of 

 these areas — evapotranspiration losses and surface-water- 

 ground-water relationships in Safford Valley, heavy pump- 

 ing and depletion of underground storage in Santa Cruz 

 Valley, and increasing salinity in the Wellton-Mohawk area 

 — are encountered also in other parts of the basin. In the 

 basin as a whole, more than 3 million acre-feet is pumped 

 annually from wells, and in several places water levels have 

 declined more than 30 feet in the past decade. Hydrologic 

 data are not complete enough to warrant estimates of the 

 average annual replenishment or even of the amount of 

 pumped water that returns to the ground-water reservoir. 



In some localities there has been a tremendous increase 

 in pumpage in the past decade. Deer Valley, north of Glen- 

 dale, is typical. Between 1940 and 1948, eighty large wells 

 were drilled to irrigate more than 21,000 acres, and annual 

 pumpage increased from 600 to 88,000 acre-feet. In the eight 

 years water levels declined an average of more than 70 feet 

 throughout the irrigated area and more than 20 feet in a 

 single year (1948). The average pumping lift in 1948 was 

 about 270 feet. 



Evapotranspiration losses are large in the hot deserts of 

 the Gila River Basin. Probably more than 500,000 acre-feet 



23 References: McDonald, H. R., H. N. Wolcott, and J. D. Hem, "Geology 

 and Ground-water Resources of the Salt River Valley Area, 

 Maricopa and Pinal Counties, Arizona," U.S. Geol. Survey, 

 Mimeo rept., February 1947, 45 pp. 

 Bluhm, F. I., and H. N. Wolcott, "Ground-water Resources of 

 Deer Valley, Maricopa County, Arizona," U.S. Geol. Survey, 

 Mimeo. rept., October 1949, 23 pp. 



