228 ALKALI WATER FOR IRRIGATION 



200 second-feet (n). The Gila River (18) was found to 

 contain 1200 parts per million of total salts on June 5. 

 By June 23 it had risen to 1546 parts per million and by 

 July 8 to 1921 parts per million. 



Water from torrential rains not having time to sink into 

 the ground, especially on rather impervious soils, dissolves 

 the surface salts and carries them into the streams below. 

 Where much alkali is concentrated in the upper soil and 

 surface of the catchment basin of the rivers, the high 

 flood waters may become somewhat saline. During 1899 

 and 1900, studies of the Salt and Gila Rivers of Arizona 

 showed them to contain more salts during flood periods, 

 caused by these sudden showers, than during the low 

 stages when the salt content might ordinarily be expected 

 to be highest (8). Similarly, observations of the Pecos 

 River showed the first flood waters to contain 5100 parts 

 per million of salts, whereas later it contained only 2430 

 parts per million. The Salinas River, California, affords 

 another example of this type of concentration of salts (48) . 

 It therefore cannot be safely stated that high waters are 

 best for irrigation purposes. 



Streams with their beds running through portions of an 

 alkali stratum of soil may become excessively alkali. 

 Salt Creek, Utah, passes over a part of the bed of old Salt 

 Lake which contains large deposits of common salt. After 

 doing so, its water was found to contain 2300 parts per 

 million of total salts, of which 1629 parts per million are 

 common salt. 



Observed Toxic Limits. The exact quantity of alkali 

 which renders water unsuitable for irrigation is uncertain; 

 it varies with the soil, the crop, the rainfall, the amount of 

 water used, the drainage conditions, and a number of other 

 factors. 



