1HE IRRIGATION AGE. 81 



put into a canal as mnch water as can be got from the river. A sim- 

 ple weir is required to keep the water in the river at a certain mini- 

 mum level above the bed of the canal, or at least to keep the river bed 

 from falling below the level of the canal bed; but bottom water as well 

 as top has to be taken in, and heavy silt deposits naturally result. 

 The weir is not constructed to hold up the water much above its nat- 

 ural level, for the cost of doing so would be prohibitive in the cases of 

 a small canal; if a considerable drop or fall were made in the river be- 

 low the weir, the foundations of the weir would have to be very deep 

 and massive and the flooring of great length, to withstand the pres- 

 sure and sc.ouring action of the water passing over and beneath in the 

 soil. 



In a river, where several such canal heads were fairly close to- 

 gether, it might promote efficiency and ultimate economy to amalga- 

 mate the heads into one, and let the canals branch off from a common 

 main channel. Then it might be practicable to build an efficient weir, 

 as the cost, distributed over air the canals, would not be a. financial 

 burden on any one. But every such case would have to be decided on 

 its own merits and possibilities, according to the physical configura- 

 tion of the ground. 



The practice of irrigation in America, is now showing the great 

 advantage derived from co-operation among the users of a Lateral, 

 and the efficiency and economy of having one main lateral for each 

 farm. It can readily be understood that the same principle will apply 

 to canals also; and that two or more canal heads may with advantage 

 be combined into one, if there are no special circumstances to hinder 

 such an arrangement. 



The methods of construction and of the working canals in 

 America, they resemble more nearly those of the inundation canals, 

 than those of the great perennial canals of North India. The latter 

 are really monuments of engineering skill, enterprise and manage- 

 ment; so much so, that professional pride in and love for them, on 

 the part of their designers and constructors, has usually tended to 

 obscure in their minds, the special merits and uses of the simpler 

 inundation canals, which requires for their design and construction, 

 usually no great engineering skill. As has all ready been explained 

 the chief advantage of an inundation canal, is that its proper use does 

 not tend to swamp land by raising the subsoil spring level so much as 

 perennial canal irrigation would do. In the bottom lands bordering 

 a river, where the water is not far down below the ground surface 

 and can economically be raised from wells for irrigation during the 

 Indian cold weather months. Inundation canals are best stilted to the 

 land. But in the higher lying lands more remote from the rivers, 

 perennial canals alone will satisfy all requirements, and are a neces- 



