408 WOOD TRANSPORT BY WATER. 



1. Rafting -channels. 



In order that rafting may be possible, generally it is necessary 

 that the water in a stream should flow uniformly and gently, 

 with only a slight fall. In well-regulated rafting-channels a 

 smaller head of water is required than in mere floating-channels, 

 but the depth must not be less than 2 or 2J feet. Although 

 rafting may be done more favourably on the lower courses of 

 streams and large placid rivers,* yet sometimes higher moun- 

 tain-torrents are thus utilised. In such cases, however, where 

 the channel is full of rocks and boulders and has a consider- 

 able fall, a larger head of water is required than for floating, 

 for unless the rafts are carried over all obstacles in the water, 

 they will be stranded and broken-up. 



In the latter case, therefore, artificial supplies of water are 

 requisite, and both reservoirs and weirs placed along the stream 

 are employed to increase the head of water. The latter are 

 either sunken weirs with a long wooden wall in the middle of 

 which there is a passage which may be closed, or stone 

 overflow - weirs. Keservoirs are not so valuable for 

 rafting as for floating, as they do not concentrate the 

 water in a certain part of the rafting-channel. On the other 

 hand, this may be done effectively by placing weirs at 

 short distances apart along the channel, when the water can 

 accumulate between any two weirs to the height required by 

 a raft. 



Wherever the sections and rafts are made-up in powerful 

 streams, a side-channel or basin is required wide enough for 

 the logs to be turned and placed alongside one another. In 

 smaller streams this is best secured by constructing weirs at 

 places with shelving banks. In the upper portion of rafting- 

 channels the rafts may be made-up in the bed of the stream 

 at any suitable place with shallow water. It has been already 

 remarked that tanks are used to supply water to rafting- 

 channels ; they are preferable to any other mode of strengthen- 

 ing the head of water, as they permit rafting to be carried-on 

 without interruption. 



* In 1883, a raft consisting of eleven sections, each containing 500 logs, and 

 800 ft. long, was towed GOO miles from St. John in New Brunswick to New 

 York in ten days by two powerful steam-tugs. 



