258 



SOIL PHYSICS AND MANAGEMENT 



The area of land that may ultimately be brought under irriga- 

 tion is small in comparison with the total dry-land area, because 

 the total supply of water is not sufficient for more than one-tenth 

 of the dry land. At present only about one per cent of the land in 

 the western states is irrigated. The building of such reservoirs 

 as are given in the preceding table is extending the irrigated area 

 more than was supposed to be possible a few years ago. 



Area and Projects. In 1009, 13,739,499 acres of land were 

 irrigated in the arid states. This was an increase of 82 per cent in 

 ten years. In 1910 the projects, then started, will be capable of 

 irrigating 19,335,711 acres when fully under way. The total area 

 included in the projects is 31,112,110 acres. In addition to the 



FIG. 113. Fia. 114. 



Fio. 113. Conduit for conducting water to where it maybe used for irrigation. (U. S. 



Reclamation IService.) 



Fia. 114. Concrete-lined canal that permits no loss by seepage. (U. S. Reclamation 



Service.) 



above, 724,800 acres of land were irrigated in humid areas, nearly 

 all of which was for the growing of rice. 



The United States Reclamation Service, established in 1902, 

 was to use the money from the sale of public lands in the arid states 

 in the construction of irrigation systems. Under the direction of 

 Dr. F. H. Newell immense projects have been started, many of 

 which have been completed, and by which large areas have been 

 reclaimed and added to' the country as some of its most valuable 

 assets. 



Sources of Water. (a) Diversion of Streams. The com- 

 mon source of water for irrigation has been the diversion of parts 

 of streams at a height above where it is to be used and conducting 

 it by means of canals, tunnels, conduits and ditches to where 

 it is to be distributed over the land (Figs. 113 and 114). 



