FARM IRRIGATION 243 



East, except, perhaps, in the special cases noted 

 above. 



SUPPLY OF WATER FOR IRRIGATION 



The most common source of water for the large 

 irrigation systems is a river or smaller stream. It 

 is extremely fortunate that most of the arid sections 

 of our country are traversed by streams which have 

 their origin in highlands, where the rainfall is much 

 greater than in the plains, and so the streams are 

 never-failing. Some western streams, notably in 

 southern California, do not appear on the surface 

 except in freshets. They exist below the sur- 

 face, however, in a very real sense, as a well 

 defined body of water, seeping through the soil 

 in a definite channel. Such streams may be 

 dammed below the surface and used for irrigation ; 

 or wells may be sunk in or near the dry river bed and 

 the water pumped up. Innumerable wells have 

 been sunk in southern California for this purpose, 

 especially during the recent series of years of 

 extremely scanty rainfall, ending in 1900. 



Occasionally lands are irrigated from a lake or 

 pond, but more frequently from a special storage 

 reservoir made by damming a stream. Some of 

 the most notable irrigation systems in the West are 

 supplied by masonry reservoirs built at a great 

 cost. It is a part of the Government's plan, under 

 the Reclamation Act, to build immense reservoirs 

 among the foothills for storing the water derived 

 from the rain and melting snow on the mountains. 

 Whether covering a few acres or many square 

 miles, these reservoirs are constructed at strategic 

 points, as in a natural depression, like a deep, 

 narrow valley or canon having only a narrow 



