IRRIGATION 135 



or ten acres one inch deep. The principal advantage of this 

 unit lies in the fact that a direct comparison may be made 

 between the irrigation water applied and a similar amount 

 of rainfall. Where water is delivered from a canal, it is 

 necessary to use a unit which will indicate the rate of delivery. 

 The cubic foot per second is a unit in common use, and is 

 easily understood. The miner's inch, used in many states, 

 is a unit whose value varies very much. In Idaho, Nevada, 

 and Utah, laws have been enacted denning a miner's inch 

 as 1-50 of a cubic foot per second. In Arizona, it is 1-40 

 of a cubic foot per second, and in Montana a unit having 

 the same value is called a statute inch instead of a miner's 

 inch. In Colorado, a cubic foot per second is equal to 38.4 

 statute inches. Water is usually measured by weirs, which 

 are notches of a certain form through which the water is 

 allowed to flow. A form of weir in general use is known as 

 the Cippolletti. The amount of water flowing through such 

 a weir may be determined from the height, or "head," of the 

 flow. 



QUESTIONS 



1. What are some of the principles involved in applying irrigation 

 water? 



2. What are some of the essential features of preparing land for 

 irrigation? 



3. How does the cost of preparing land for irrigation vary with 

 methods of irrigation? 



4. Describe the flooding method of applying irrigation water. 



5. Explain the check method of applying water. 



6. Describe basin and border irrigation. 



7. How is irrigation water applied in furrows? 



8. Why is subirrigation not generally satisfactory? 



9. How is irrigation water applied by spraying? 



10. What are the units in general use for measuring irrigation 

 water? 



11. What is a weir? 



