FLOATING. 



375 



therefore, where such damage is to be feared, weirs should be 

 furnished with sluice-gates, which may be opened when there 

 is danger of a flood. 



Fig. 247 shows a section through the middle of a weir in 

 which a sluice-gate is supplied, m o n being the section of the 

 weir, and o m the sluice-gate with a sloping base (s m), 

 enclosed by wooden horizontal walls ; this gate is closed when 

 the water-level is at its ordinary height, but can be opened in 

 floods. 



More frequently, however, a ground-weir is erected with a 

 number of sluice-gates arranged side by side, by opening 



L'I7. \\Vir with sluice-gates. 



which all the water may pass in high floods or the timber be 

 allowed to float through. 



It has been remarked already that certain works may be 

 necessary to keep silt, gravel or boulders out of reservoirs ; 

 these works are merely weirs made of wattle-work or stone, 

 across the small brooks which feed the reservoir, and thus the 

 results of denudation of the hill-sides are kept from descending 

 the watercourse. In addition to these weirs, the ordinary 

 measures should be adopted for fixing the slopes on either 

 side of a mountain-torrent, and keeping it stocked with forest 

 growth. 



(b) Works for regulating the Course of a Natural 

 Stream. 



There is not a single watercourse, which is naturally so suit- 

 able for floating timber, but that it may be improved by some 



