DUTY AND DIVISION OF WATER 363 



lateral under this system carries 2 second-feet of water 

 continuously, and is, therefore, to be reserved for 200 

 acres. This means that the whole 200 acres could be 

 covered by this stream, to a depth of 4 inches, every six- 

 teen and two-thirds days. In other words, each farm 

 under this lateral would receive its allotment of water 

 every sixteen and two-third days. If the 200 acres under 

 this lateral consist of six farms of 5, 10, 20, 25, 40 and 

 100 acres respectively, it may easily be calculated that 

 they would receive water every sixteen and two-third 

 days as follows: 



Length of irrigation period (every 16% 

 Area of farm days, or 400 hours) 



5 acres 10 hours 



10 20 



20 40 



25 50 



40 80 



100 200 



200 " 400 " 



If the stream were larger, the time for each farm would 

 be correspondingly decreased. Such a system may be 

 followed easily by the water-master and is readily under- 

 stood by the farmer. 



Another application of the rotation method is to fill 

 the mam laterals in rotation. One or a few laterals are 

 given all the water of the canal for a certain number of 

 days; then another set of laterals, and so on, until the 

 rotation has been accomplished. This system is not so 

 satisfactory to the farmer as the preceding one, because 

 a whole district is for a time without water, when the 

 neighboring district has an abundance. Under the first 

 system all districts under the canal are at all times doing 

 some irrigating, and the presence of the water gives the 

 farmer a sense of security. 



