IRRIGATION INVESTIGATIONS 



G. E. P. Smith, W. E. Code, H. C. Schwalen 



The last annual report of this department covered the 

 progress of investigations up to the end of the calendar year, 

 as had been the custom in former years. This report, there- 

 fore, covers the period from January 1 to June 30, 1921. 



GROUNDWATER STUDIES 



A survey of the water table in the Casa Grande Valley 

 was made in midwinter and another survey in June to deter- 

 mine the recovery from the severe pumping draught of 1920 

 and the subsequent depression due to the much lighter draught 

 of 1921. The fact that in the main pumping district there was 

 a residual loss in the supply at the beginning of the 1921 sea- 

 son is evidence that the rate of pumping in 1920 exceeded the 

 normal recharge and that the total water supply pumped in 

 1920 represented quite closely the capacity of the ground- 

 water supply. However, it has been proved by the well rec- 

 ords that there is an important gain or recharge due to irriga- 

 tion from the Florence Canal, and the recent completion of the 

 concrete diversion dam at the head of that canal, to replace 

 the temporary brush and gravel wing dams used heretofore, 

 will undoubtedly augment the groundwater recharge from this 

 source. 



The extensive information concerning the groundwater 

 supply in the Casa Grande Valley that has been collected by 

 this department has been furnished the Land Classification 

 Board of the United States Geological Survey for its use. 



A possible groundwater irrigation project of modest pro- 

 portions in the San Simon Valley is being studied. A contract 

 for a well for exploratory purposes in the vicinity of the Cien- 

 ega has been let, the location being the southeast corner of 

 Section 34, Township 15 South, Range 32 East, on State land. 

 The well is within the terrace which delimits the Recent valley 

 fill, and, besides showing the pressure conditions at considerable 

 depth, will furnish data for estimating the probable yield of 

 individual wells and the possible groundwater development by 

 pumping in that district. 



The St. David-Benson artesian district has been studied 

 by means of a survey of the artesian wells, their locations, 

 pressures, and yields. Piezometric lines show conclusively that 



