388 



WATHI^TKANSPOKT 



floating spruce stems arc pliiceJ to take the shock of the floating 

 wood from the grating. Where the stream is broad and the 

 grating long, supports are also uecessar}', their simplest mode of 

 construction being shown in lig. 2'20. 



Fio. 229. 



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

 tion ; in the case of wooden supports, piles are driven sufticiently 

 deep into the Arm (rocky) bed of the stream, niid when there are 



Fig. 230. 



masonry-supports, by a lirm foundation of piles, in case a rocky 

 base cannot be reached. Fig. 230 represents a large boom over 

 the river Regeu, at Regensburg ; in this and other large 

 booms the supports are similar to those used for large bridges, 



