386 



WOOD TEANSPORT BY WATER, 



rest without any support -on the bed of the stream. In front 

 of them, floating spruce stems are placed to take the shock 

 of the floating wood from the grating. Where the stream is 

 broad and the grating long, supports are also necessary, their 

 simplest mode of construction being shown in Fig. 257. 



The supports of large booms require, above all, a solid 

 foundation : in the case of wooden supports, piles are driven 



Fig. 259. Boom with removable grating. 



sufficiently deep into the firm (rocky) bed of the stream ; wlu>n 

 there are masonry-supports, a firm foundation of piles is sup- 

 plied, in case a rocky base cannot be reached. Fig. 258 repre- 

 sents a large boom over the river Kegen, at Regensburg ; in 

 this and other large booms the supports are similar to those 

 used for large bridges, they are arranged with their longest 

 sides parallel to the stream so as to offer as little resistance to 

 it as possible. Of a similar construction is the large boom at 



