296 Irrigation and Drainage 



The dangers in this direction will be least in countries where 

 the natural drainage facilities are best ; where the streams, draws 

 and washes are sunk deepest below the surface of the fields; 

 and where the subsoil is the most open, thus providing an easy 

 escape of the seepage waters into the natural drainage channels. 

 Under such conditions as these, it would be only the most waste- " 

 ful, extravagant and inexcusable use of water, with no attention 

 to proper methods of tillage, which could lead to the evils 

 pointed out. 



But, on the other hand, in countries where the natural 

 drainage lines are shallow and few, and where the soil and 

 subsoil are close, it will require the greatest vigilance and the 

 rarest skill and judgment to avert the evils of swamping, the 

 development of a malarial atmosphere, and the formation of 

 alkalies. If, in addition to the conditions last pointed out, the 

 irrigation water is naturally heavily charged with undesirable 

 salts, then the situation becomes as serious as possible. 



When capital, therefore, is seeking permanent investment 

 in the development of an irrigation system, the difficulties 

 pointed out are matters for first and most serious consideration; 

 and when agriculturists propose to establish homes under such 

 surroundings, the same serious attention should be given the 

 probable permanency of the conditions of fruitfulness and health- 

 fulness. 



It sometimes happens that water for irrigation must be taken 

 from mountain canons and led out upon the mesas and over the 

 valleys under great difficulties, such as tax the highest engi- 

 neering skill to its utmost to accomplish. As an illustration of 

 this type of irrigation engineering, the case of one of the canals 

 supplying Eedlands, California, may be cited. In Fig. 57 the 

 dark line on the flank of the mountain on the right is an open 

 canal, with cement masonry lining, which winds up the valley 

 until it can draw its supply from the Santa Ana river. Lower 

 down the mountain valley it becomes necessary to cross the canon, 

 and this is accomplished by using the large redwood siphon rep- 

 resented in Figs. 58 and 59. This gigantic pipe has an inside 

 diameter of 4 feet, and in one portion of its course is obliged 



