322 THE IRRIGATION PROBLEM. 



It is plain, on the slightest consideration, that the cost of a canal 

 will be so dependent on local and special circumstances that it is 

 impossible to deduce a perfectly satisfactory conclusion from a 

 given or hypothetical case. 



The dam, the character of the soil, the quantity of land to be ir 

 rigated, the manner in which it is disposed, the relative remoteness, 

 and the resources and population along the line are all elements 

 which vary from case to case, and either of which may effect the 

 cost by a very considerable per centage. 



Still it seems essential to know within some limits the probable 

 cost. 



If a canal is to cost $100 per acre irrigated, the subject may be 

 dismissed without any further consideration. It is plain that we 

 cannot afford to pay that price. If, on the other hand, canals may 

 be built for five or twice five dollars per acre, it is equally plain that 

 now or before many years we shall be able to afford them, and shall 

 have a fair prospect of return from such investment. 



The value of the estimate which we proceed to give, will be un 

 derstood from what proceeds. 



Let us take the most favorable case that can happen, namely, 

 when the excavation equals the embankment. We assume a canal 

 to carry 315 cubic feet of water per second, having the dimensions 

 given in the figure. Deducting from this 15 per cent, for loss, the 

 water available for irrigation is 268 cubic feet, which will irrigate 

 53, GOO acres. If we suppose the irrigable land to lie 011 one side 

 of the canal, in a strip five miles wide, and that the ground permits 

 straight parallel primary ditches spaced one mile apart, it follows 

 that for each mile of canal there must be five miles of primary 

 ditches, and that the quantity of irrigable land for each mile of 

 canal will be 3,200 acres. Deducting one fourth for land not 

 actually watered, we shall have 2,400 acres of irrigable land for 

 each mile of canal. 



Let us take a primary ditch of capacity to carry 50 feet of water 

 per second. Allowing for loss, this size will be rather more than 

 sufficient to cover the 2,400 acres with three inches of water in seven 

 days and seven nights. The canal can fill at the same time six of 

 the primary ditches, so that in seven days 14,400 acres can be covered 

 with three inches of water, only six of the primary being full at 

 the time. And in twentj^-six days three inches of water may be put 

 over the whole amount of the land, namely, 53,600 acres. 



If the water is used only for fourteen hours each day, the time 

 necessary to go over all the land with three inches of water will be 

 forty-five days. 



Under our hypothesis, in order to irrigate 2,400 acres, we must 

 build one mile of main canal and five miles of primary ditches. 

 Placing the excavation at 30 cents per cubic yard, we find the 

 cost per acre to be about $5. 



The section of the main canal will diminish towards its lower end, 

 but to be on the safe side, so far as cost is concerned, we keep it of 

 uniform size. The price of excavation may be somewhat in excess 

 of its actual cost in some places; but inasmuch as in it are included 

 all incidental and contingent expenses, we believe it is not far from 



