FLOATING AND RAFTING 391 
a tight face is made or else planks must be spiked to the timbers 
in order to make the dam tight. 
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 is placed on either side to 
care for the surplus flood water. The sides 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 m.ake it tight. The cribs are 
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 and to protect the 
base of the structure. 
Where the stream bed is unstable a row of piles is sometimes 
driven across the dam site near the center of the sluiceway. 
These are cut off at the stream bed level and prevent the bottom 
from washing out. 
Rafter or Self-loading Dam. — This type is cheaper to build 
than a crib dam and is used where a large head of water is not 
required. 
Rafter dam foundations are constructed in the same manner 
as crib dams with pockets 6 by 6, or 8 by 8 feet in size. The mud- 
sills are drift bolted to bedrock when possible. As the framework 
is built up, the face of the dam is drawn in from the level of the 
stream bed so that the upstream face has an angle of 3 horizontal 
