IRRIGATION INVESTIGATIONS 



G. E. P. Smith, \V. E. Code 



In November, 1918, this office was strengthened by the appoint- 

 ment of W. E. Code as Assistant Engineer. The position had been 

 vacant for eighteen months, owing to the Great War. In Jnnc. 

 1919, H. C. Schwalen was added to the staff in order to assist in 

 the extensive investigations in the San Simon \'alley and to carry 

 on extension service work relating to pumping for irrigation. 



THE CAS A GRANDE VALLEY 



Conditions have been favorable for continued study o; the 

 groundwater supply. Unusually heavy rainfall has aided in the 

 investigations of recharge and the large acreage under i)ump irri- 

 gation, 5200 acres, has made possible definite conclusions on the 

 effect of pumping on the groundwater table. The rapid develop- 

 ment of the valley agriculturally has added interest in the con- 

 clusions to be drawn from these studies. 



Surface runoff measurements have been made with more preci- 

 sion than in any previous year. The river discharges at Tucson 

 for the year 1919 were 42,200 acre-feet for the Rillito and 28,700 

 acre-feet for the Santa Cruz. The discharge at Sasco was 57,200 

 acre-feet, 10,500 acre-feet of which was from the Robles Wash. 

 The loss, therefore, by seepage between Tucson and Sasco was 

 24,200 acre-feet plus the flow from Canada del Oro and a few small 

 tributaries. Of this flow, 6,800 acre-feet reached the Southern 

 Pacific Railroad at Eloy and 7,900 acre-feet at Lirim and Mari- 

 copa, representing a loss of 42,500 acre-feet between Sasco and the 

 railroad. 



A large percentage of the water that passed Eloy did not reach 

 the Gila River. On two occasions when floods of considerable 

 magnitude passed Eloy the water did not reach to the main high- 

 way leading east from Casa Grande. 



The Santa Rosa Wash which drains a large area to the south, 

 debouches upon the Casa Grande Valley at a point 14 miles south- 

 west of Casa Grande. The waters of this wash spread over the 

 valley and the flow crosses the Southern Pacific Railroad near 

 Maricopa. The flows are intermittent and usually of short dura- 

 tion, bat it is thought that they have some value in replenishing 

 the ground w^aters on the western side of the valley. During dry 

 vears the run-off is practically negligible. 



