398 



WATKK-TRANSPOllT. 



fore, the fall of the stream is considerable, it is usually 

 sufficient to place the boom out of the main current by allowing 

 surplus water to pass off by a side-channel ; or, when the boom 



Fio. 238. 



is in a side-channel, a deep and steeply inclined cut, termed a 

 sand-canal, is made in the latter to carry the sand and boulders 

 into the main stream. Fig. 239 shows the floating-channel (s, s), 

 which bifurcates from the main stream, H ; (m, m) form so many 

 cuts between strong, solid masonry walls, which may be closed 

 by lateral booms and sluice-gates ; ((/) is the sand-canal, which at 

 (^0 is only half a meter deeper than the rest of the floating 

 channel, but deepens gradually towards (]>). The boulders which 

 accumulate in {d, ]>) are passed through a temporary opening (jj) 



