144 HORTICULTURE FOR SCHOOLS 



judgment of its engineers are practicable and which on 

 account of the time and money involved would be out of the 

 question for private capital. Along these lines some notable 

 undertakings have been carried to completion. The immense 

 amounts of money and the engineering skill required were 

 not available to any individual or the ordinary corporation, 

 and the Reclamation Service performed a task which other- 

 wise would perforce have gone undone. How great have 

 been the benefits the following statistics will abundantly 

 show. At the beginning of the year 1920 a total area of 

 18,191,716 acres had been put under irrigation. The value 

 of products obtained from these farms in 1919 reached the 

 vast total of $801,005,326. 



236. Irrigation in humid regions. In one sense, and 

 especially in some localities, irrigation is a form of insurance. 

 Rainfall may be abundant, if the total annual precipitation 

 is taken into account. But it may be lacking at those times 

 when it is most critically needed; and an irrigation plant 

 would justify itself even though it might be used only at 

 long intervals. It is on this basis that provision for irriga- 

 tion has been made on many farms in the humid sections 

 of the United States. 



237. Sources of water. Water may be secured from 

 mountain streams by the simple process of diversion to 

 canals; or it may be stored in reservoirs during the rainy 

 season, and this supply may then be drawn on as needed; 

 or it may be obtained from the underground supply. 



238. Diversion of streams constitutes the most obvious 

 means of obtaining water. Immense quantities of water are 

 carried constantly in the rivers that flow to the seven seas 

 of the world, and if this could be utilized in the growing of 

 crops the gain to mankind would be very great indeed. 



There are many examples in the United States of diversion 

 of stream flow on a large scale. The Uncompahgre project 

 in Colorado is one of the largest in the history of irrigation 



