CHAPTER X. 

 DUTY AND MEASUREMENT OF WATER. 



I 



N order to determine the amount of land which 

 can be served by the flowing water of an irri- 

 gating season and by the storage of water of 

 the non-irrigating season, it is necessary to 

 ascertain the quantity of water which should be used 

 in serving a definite area of land. This is called by 

 irrigation engineers the duty of water, which, by the 

 way, is aifecfled by the amount of rainfall, the artificially 

 supplied water being complementary to it. It is also 

 affedled by latitude, altitude and other climatic con- 

 ditions. It is further affe(5led by the character of the 

 soils, and finally depends largely upon the kind of crops 

 raised. 



In the storage of water, in order to determine the 

 amount which can a(5lually be conserved for useful pur- 

 poses, it is necessary to ascertain the extent and the 

 rate of evaporation under different conditions of lati- 

 tude, altitude and general climate. Local condition, 

 charac5ter of the soil, slope of the land, cultivation, 

 humidity, evaporation, precipitation, drainage and 

 capillary action are so widely at variance in different 

 localities that there is small hope of getting any formula 

 which will admit of extended application. Crops differ 

 with respedl to moisture requirements. For example, 

 oats and wheat will require more than rye and barley, 

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