178 IRRIGATION. 



and distributing apparatus, is much higher than would 

 be necessary here, being made with scrupulous care for 

 economy in both water and land ; and the cost of super- 

 vision is much higher than would be likely to occur here. 

 Unless costly dams, expensive bridges, and aqueducts, 

 built with a view to the utmost permanency, should be 

 required, there would probably never be any approach 

 made here, to the high cost of water that is experienced 

 in European countries. Some of the European works, 

 now in operation, have been in existence for more than 

 1,500 years. Others abandoned, but still in serviceable 

 condition, are over 2,000 years old. 



The quantity of water needed for irrigation, as has 

 been already explained, varies greatly, and in making 

 estimates of the amount required, for any stated territory, 

 the engineer or irrigator must necessarily study both soil 

 and climate. Where exhaustive circumstances belonging 

 to either are found, reasonable allowances must be made. 

 A maximum consumption, as indicated by experience in 

 Colorado, as well as by comparative estimates in foreign 

 countries with arid climates, may be considered to be, 

 one square inch per acre continually flowing ; and an 

 average consumption to be 72 square inches per 100 acres 

 continually flowing at the rate of four miles per hour, or 

 half a cubic foot per second. This estimate, however, 

 does not include the loss by evaporation, or soakage 

 through the bed of the canal ; losses which, in one of the 

 Californian canals, amounts to more than 40 per cent of 

 the quantity entering the mouth of the canal, and is 

 therefore seen to be a very serious item of consideration 

 by the hydraulic engineer. Some further remark upon 

 this important point will be found in the chapter on 

 Canals further on, to which attention is directed. 



The art of irrigation, however, is in its infancy with us 

 as yet ; and although we enjoy some special advantages, 

 there are some things to be learned before the full benefit 



