352 LOGGING 



for labor and materials, exclusive of the value of the timber 

 used. 



Where the stream bed is sandy and rather unstable a row of 

 piling 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. A dam of this 

 character which was lo feet high was constructed at the follow- 

 ing cost : 



Cutting and skidding 170 piles $ 45 



Driving 170 piles 210 



Cutting and skidding crib timbers (5500 board feet) 15 



Crib building 90 



Dam gate construction 10 



Building embankment and clearing up reservoir in rear 250 



Total $620 



Four men were occupied twenty-one days in driving piles and 

 ten days in building the structure. In addition one team and a 

 driver were required for three days to skid the timber. Other 

 workmen cut the piles and crib material. The embankment was 

 made largely by hand labor and w^as not included in the thirty- 

 one days. 



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 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 

 to I vertical. The dam should be at least 8 feet wide on top. 

 Two thicknesses of 3-inch plank or hewed poles are spiked on the 

 sloping face, the joints being alternated and the whole covered 

 with a bed of gravel. The rear mud-sill is protected by toe- 

 spiling driven down to hard clay or bedrock, and the cribs are 

 weighted down with stone. A dam of this character, 200 feet 

 long and 10 feet high was built in the Adirondacks at a cost of 

 $1600. A similar dam 60 feet long and 10 feet high was built 

 in Canada for $700. 



