FLOATING. 



399 



and the corresponding sluice-gate in the lateral boom, and pass 

 along )ii into the main stream //. 



Simple sand-canals can only be opened for the passage of silt, 

 &c. whilst floating is not in progress. In order to free a float- 

 ing-channel from these accumulations during the floating, they 



Fig. 239. 



may, as at (q) (fig. 239), be covered with a wooden lattice-work 

 (fig. 258) constructed at the bottom of the floating-channel (s). 

 Besides this method, double booms may be used, which are erected 

 the one close behind the other, and the silt and boulders are 

 admitted into the interval between them by opening the first 

 boom and then passed through the second boom, so that always 

 one of the booms is ready to stop the floating wood. In order 

 also to expose the bed of the stream in front of a boom and then 



