396 



WATER-TRANSPORT. 



across the river IIz near Passaii, built as iu fig. 230 ami a plan 

 of which is given in fig. 230, collects over ten thousand saw-mill 

 butts, and allows for their being continually removed by the 

 underground channel {a). 



ii. Lateral Booms. 

 These booms are intended to divert floating timber into a side 

 channel, and are long and oblique. 



In powerful floating-channels, a terminal boom cannot usually 



be laid across the main 

 stream without danger of 

 being broken. In such 

 cases, therefore, a side 

 channel is diverted from 

 the main stream and the 

 sweep of timber conducted 

 into it, the main stream 

 being barred by a boom. 

 Fig. 237 is a long lateral 

 boom, only closed in the 

 middle by floating logs. 

 II is the main stream ; 

 s, the side-channel, lower 

 down in which the ter- 

 minal boom is placed ; h 

 is a weir diverting water 

 into s. As in this case 

 the pressure of the sweep 

 of wood and of the stream 

 is divided between two 

 booms, neither of them 

 need be very strongly 

 constructed. This is the chief advantage of leading the floating 

 wood into a side-channel. AVhere a natural bifurcation of 

 a river does not exist, an artificial side-channel is frequently 

 constructed with advantage ; if, then, the lateral boom is sup- 

 plied^with a strong weir, or, if possible, with a sluice-weir, the 

 supply of water to the side-channel may be regulated at will. 

 On this general principle are founded all the better kinds of 



