30. IRRIGATION AND DRY FARMING. 



Irrigation. In the West, there are vast tracts of land 

 where but little rain falls. These are commonly known as 

 arid regions. There are other great areas where rain falls 

 only during the winter season. In order that crops may 

 be grown in these regions, it is absolutely necessary that 

 water be supplied by irrigation. 



FIG. 97. Dam of an irrigation reservoir. 



Methods of Irrigating. Water for this purpose is often 

 obtained from wells, and sewage from cities is sometimes 

 used on farms lying near, but most of the water used comes 



from streams. When there is any likelihood that the stream 



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