FLOATING AND RAFTING 35 1 



row of mud-sills into which they are notched so as to rest 

 firmly. Logs with two hewed faces are then placed on top of 

 the cross-skids to which they are drift-bolted. These lie parallel 

 to the mud-sills. All timbers on the upstream side of the dam 

 are hewed down and fitted to each other so that a tight face is 

 made. 



A cribwork is built up until it reaches the level of the stream 

 bed, when it is necessary to provide a "sluiceway" through 

 which logs may pass and also gates through which surplus water 

 may be wasted. Sluiceways are generally from 9 to 15 feet 

 wide and are placed in the center of the natural stream bed. 

 A sufficient number of waste gates are placed on either side to 

 care for the surplus flood water. The slides of the sluiceway 

 and of the waste ways, both of which carry headworks for gates, 

 are made stronger and of larger logs than the rest of the structure 

 and are often reinforced with piers. In building waste gates 

 and sluices the transverse sills are cut off where the opening 

 begins and the cross-skids which form the side walls of the sluice 

 have smooth hewed faces that fit closely together. The cribwork 

 of the dam is then continued to the desired height. When 

 finished the upstream face of the dam is calked with tow or 

 boarded up with 3 -inch plank to make it tight. The cribs are 

 often roughly floored with puncheons and filled with rock to 

 weight them down. The cover of boards on the face is sometimes 

 replaced with a bed of gravel although both boards and gravel 

 are frequently used. 



Piers are often constructed on each side of the sluiceway above 

 the dam to confine the water, strengthen the dam, and prevent 

 the structure from being undermined. 



An apron also extends out from the sluice on the lower side 

 of the dam to carry the water and logs away from its base 

 and prevent the wearing away of the earth around the foun- 

 dations. 



A crib dam of hewed timber which was built in Wisconsin a 

 few years ago was 12 feet high, 20 feet wide and 400 feet long. 

 The cribs were filled with stone and a roadway was built on top 

 of the dam. The cost of construction was approximately $4000 



