52 



DIVISION OF WATER RESOURCES 



PLATE V 



MONTHLY USE OF WATER BY SALT GRASS IN TANKS HAVING VARIOUS 



DEPTHS TO WATER TABLE. 



Although the presence of salt grass is always an indicator of 

 ground water, these experiments have demonstrated that its consump- 

 tive use is not excessive when compared with water requirements of 

 many cultivated crops. In general, farming operations are conducted 

 on water-free soil of sufficient depth to allow ample root development. 

 The average depth to free water naturally varies with each locality, 

 but a minimum of 5 or 6 feet is considered a safe depth for many field 

 crops. For the 12-month period ending April 30, 1932, salt grass 

 grown in tanks having a depth of 5 feet to water table, used an average 

 of about 22 acre-inches of water, including rainfall. During this 

 period, conditions were the same as in natural salt-grass areas. This 

 consumptive use is no more than that used by various crops of low 

 water requirement, and is less than amounts required by alfalfa, citrus, 

 or walnuts. In tanks having a water-table depth of 2 feet, the 12-month 

 consumptive use for the same period was about 36 acre-inches per acre, 

 which is sufficient, with careful management, to produce a fair crop of 

 alfalfa. In most salt-grass areas in the Santa Ana basin the ground 

 water occurs at depths exceeding 4 feet and the average seasonal draft 

 is, therefore, Ioav. It is concluded, therefore, that the yearly water 

 requirement of salt grass in this area is generally less than that of 

 cropped lands. 



Data on the weekly use of water by salt grass at the Santa Ana 

 station from May 7, 1929, to November 3, 1931, are given in Tables 11 

 and 12. On the latter date, readings at the station were discontinued, 



