FLOATING. 361 



a rich water-collecting basin, its springs and brooks running 

 through the forests ; if here, not only the less important springs, 

 but also the brooks of adjacent valleys are united to the floating 

 stream by canals, and its tributaries provided with sluices, the 

 best possible measures will have been taken to gain a sufficient 

 water-supply. 



Lines of levels should be run for these projected feeders, 

 which must often be conducted round spurs and precipices so as 

 to secure, if possible, a uniform fall, which should rarely exceed 

 ■^ to oV 01' serious damage may ensue. Sluices are required 

 where the feeder leaves the brook, the water of which is to be 

 utilized, and also where it joins the floating-channel, so that 

 swollen torrents maybe avoided, and water admitted to the latter 

 only when it is required. It must not be supposed that it is 

 always a difliculi, matter to lead water from one basin into 

 another, for in the upper parts of a mountain-range several 

 streams may be quite adjacent which diverge widely lower down ; 

 the feeding-canals also are not difficult to construct, being usually 

 mere trenches like those used in irrigating meadows, and it 

 is usual to utilize only tributaries of the same stream which 

 eventually join it lower down. 



The direct line of floatage is not often supplied by feeders, but 

 they are frequently used to fill reservoirs. 



iii. Dams and Reservoirs. 



AVhenever lakes and ponds are not available, the water of the 

 floating-stream itself may be dammed-up, and thus a stronger 

 head of water obtained. This is secured by means of a dam 

 furnished with a sluice-gate, which is erected transversely across 

 the valley in which the stream runs so as to maintain the level 

 of the water behind it. A reservoir is thus formed, the water 

 in which may be made available for floatage when required, by 

 opening the sluice-gates. 



There is much variety in the mode of construction of dams, 

 and according to the material used for them, they are made of 

 earth, wood or masonry. 



The chief point is to make the dams and sluices watertight ; 

 cemented masonry-dams are best in this respect, but earth-dams 

 are superior to wooden sluices. 



