REMOVAL OF BARS AND OTHER OBSTRUCTIONS. 49 



The advocates of the method of dynamite, among whom are experienced engineers, 

 claim that the explosion loosens the material for a wide distance, and thus enables the 

 current to remove it. Experiments with eggs buried in the sand showed that one was 

 broken at a distance of no feet, while others, from 115 feet to 315 feet away, were 

 unharmed, the charges being, it is believed, about 100 pounds.* 



Snagging. In order to make navigation safe it is frequently necessary to remove 

 such obstructions as snags, rocks, wrecks, etc., and to cut such overhanging trees as 

 may interfere with craft. This work is known as "snagging." Nearly all navigable 

 rivers of importance in this country have steam snag-boats, provided with suitable 

 grappling and lifting appliances, explosives, tools, diving apparatus, etc., and go over 

 the rivers at the most favorable times to remove obstructions. The snags are some- 

 times cut or sawed into short lengths and placed upon the banks, where they will dry 

 out and float off when a rise appears; sometimes they are boated to deep pools and 

 dropped, sinking to the bottom; and sometimes they are split up by dynamite, dried 

 out, and burned. On rivers of small draught where steam snag-boats could not move 

 about during the low-water season, the work is done with tools and explosives carried 

 on push-boats or bateaux. These boats are usually 10 to 15 feet in width, and 75 to 

 100 feet in length, and draw but a few inches of water. They are propelled by the 

 crew by the use of poles. As they can move on a small depth of water, the low-water 

 season is selected for the work, and it can then be done very effectively and econom- 

 ically, the snags all being in sight. 



On some rivers, as, for example, the Ohio, wrecks of barges are a frequent cause 

 of obstruction. The large tows occasionally become unmanageable and strike bridge 

 piers or other obstacles, and some of the coal boats and barges are sunk. Their speedy 

 removal is frequently necessary, particularly in the upper part of the river where the 

 coal rises pass off quickly. Dynamite is used for this purpose as far as practicable, 

 and sometimes dredging is resorted to. We have seen coal boats removed thus within 

 a few hours after sinking, so that tows could pass without delay or danger. 



One of the worst things to be contended with in many American streams is the 

 driftwood, which sometimes accumulates in piles and forms serious obstructions. 

 Tributary streams, where flowing through districts being cleared up or in which logging 

 operations are going on, put out great quantities of tree-tops, logs, trees, and drift of 

 every variety. In addition to the debris which thus finds its way into a river from 

 tributaries, the river itself when in flood undermines its banks, and brings in further 

 debris of similar character. Where these lodge in the bed they become partially 

 covered up and form obstructions to navigation. A bar which in itself is not a danger- 

 ous obstruction may thus assist in holding things which are dangerous. In fact one 

 snag rightly lodged may, and frequently does, change the course of the channel very 

 considerably. 



* Engineering News. 



