. WATER-SUPPLY. 51 



lands or watersheds of the area to be irrigated with the 

 shortest possible diversion line, or that portion of the 

 canal's course which is necessary to bring the line to 

 the neighborhood of the irrigable lands. This is 

 usually expensive and unproducftive of immediate 

 benefit, as it does not diredtly irrigate any land. The 

 disadvantages of locating the canal headworks high up 

 on the streams are serious. The country having an 

 excessive fall requires rough hillside cuttings, per- 

 haps in rock, and the line is, moreover, interse(5fed by 

 hillside drainage, the crossing of which entails serious 

 difficulties. But along the great Rocky Mountain 

 foothills this objedlion has been entirely disregarded, 

 and the English or High-line canal flows through the 

 rock-ribbed South Platte canon a distance of over 

 thirty miles before it reaches the open country, where 

 the first water is delivered to patrons. When taking 

 out a ditch in a flat country, as is often the case, the 

 work is much more simple and not nearly so expensive. 

 These conditions are often observed in the prairie 

 districts at great distances from the mountains. 



The other classification of surface waters is that of 

 the catchment area or reservoir order, and is a source 

 of supply that maybe termed artificial. Holdings of 

 water by this plan may be obtained without resorting 

 to the streams, by providing dams at suitable places 

 for catching the storm or run-off freshets coming from 

 rainfall on a vast watershed lying back of and at an 

 elevation above the reservoir site itself. In seledling 

 such sites, however, two or three cautions must be 

 observed. In no case should the water be stored in 

 main channels. Suppose there is a ravine running 



