IRRIGATION INVESTIGATIONS 



CASA Grande; valIvEy 



The groundwater investigations outlined in the last Annual Report 

 have been prosecuted. A mass of data on the groundwater table has 

 been accumulated, but since movements of groundwater may be very 

 slow, it is possible even now to draw only tentative conclusions. The 

 gauging stations at Tucson have been maintained, and new stations 

 established on the bridges and culverts on the Arizona Southern Rail- 

 way between Red Rock and Sasco, and on the Southern Pacific Railway 

 between Picacho and Maricopa. The floods of the year were very fortu- 

 nate from an investigator's standpoint, inasmuch as they were unusually 

 large, yet not destruci've to the bridges on which the gauging stations 

 depend. Special efforts were made to obtain the highest possible ac- 

 curacy in the measurements at Sasco in order to obtain the true dis- 

 charge at that point, where the Santa Cruz debouches into the Casa 

 Grande Valley. Condensed records of the stream flows are given in 

 Table XXV. 



TABLE XXV. RUN-OFF RECORDS FOR SANTA CRUZ AND RILLITO RIVFRS IN 



1915 AND 1916 



*Flow at Nunez is to westward. Thi.s flow returns north at I^irini. 

 tSeptember flood was caused by local rainfall. r, ,, c, 



Note: For previous records of Santa Cruz and Rillito at Tucson see Bull. b4, 

 Ariz. Agr. Exp. Sta., 1910, and subsequent annual reports. 



