FLOATING. 357 



lie along the line of floatage, and by means of a simple sluice 

 at the outlet of a watercourse from a lake, the level of the 

 latter may be maintained high enough to furnish a good head 

 of water for floating wood down the stream. Many lakes are 

 thus utilized. 



A small lake from which a side-stream passes into the line 

 of floatage, or which may be connected with it by a canal, 

 may also be utilized similarly, and in both these cases the 

 dams to be constructed are similar to those that will be 

 described further on. 



ii. Feeding-canals. 



Instead of lakes and ponds, watercourses near the floating- 

 channel may be utilized to raise the water-level of the latter 

 by leading their water into it. A mountain-range, through 

 the principal valley of which the floating-channel passes, is 

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

 running through the forests ; if here, not only the less impor- 

 tant 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 often must be conducted round spurs and precipices so 

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

 exceed 3 or 4 %, or 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 may be avoided, and water admitted 

 to the latter only when it is required. It must not be sup- 

 posed that it is always a difficult 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 that eventually join it lower down. 



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

 but frequently they are used to fill reservoirs. 



