FLOATING. 391 



Galicia, in which three twisted wire ropes are stretched as 

 tightly as possible one above the other and supported by 

 trestles at distances of 30 feet apart. 



Another kind of boom is formed of gabions (Fig. 264), as 

 used in Venezianisch and other places. Here, instead of 

 wooden or stone pillars, gabions of basket-work filled with 

 stones are used, which support the horizontal bars and the 

 grating-rails. The gabions are placed in a line across the 

 stream at distances of 5 to 15 meters (16 to 48 feet) apart, 

 according to the strength of the stream, and are tall enough 

 to be above the highest water-level ; their height varies, 

 therefore, with the depth of the water in which they are 

 placed. Planks are then placed from gabion to gabion, form- 

 ing a footway, and stout poles (a a a) are bound to the 

 gabions by means of withes. The grating-rails (b b) are then 

 bound to c outside the water and let down into it from the 

 footway, till each rail rests on the bottom of the river. The 

 several rails are bound by withes to a a a, and along the 

 grating floating logs are placed. 



These gabions have the advantage of costing little, of being 

 erected in a short time by the floating-gang and of being 

 repaired easily. At the same time, they are not durable, and 

 are often overthrown by heavy floods, to which they offer a 

 large, exposed surface. They are adapted specially for small 

 temporary sweeps of floating timber, chiefly on unimproved 

 mountain-torrents. 



Finally, floating booms must be mentioned. They consist 

 for the most part of spruce-logs which are united at their 

 ends by iron rings and fastened together in sufficiently long 

 chains. These chains of logs are fastened at one or both 

 ends, and float on the surface of slowly flowing streams, on 

 which floating is done only occasionally. In order to give 

 them a greater power of resistance, some of the logs are 

 anchored to the bottom of the river. In spite of this, how- 

 ever, they cannot resist a sudden flood, as has been often 

 experienced, in the breaking of such booms, especially if the 

 stream is fairly strong (the river Inn). 



[In the river Jumna, at Daghpathar, a boom is placed at a 

 point where the river is 120 yards broad, it consists of two 



