FLUMES AND LOG SLUICES 401 



Sluice boxes are sometimes made with two thicknesses of 2-inch 

 plank, the inner set being surfaced and tongued and grooved to 

 insure a tight joint, while the outer set of plank break joints with 

 the inner and make a tight box. The dimensions of a sluice 

 of this character built in the Lake States for white pine were 

 36 inches in width at the base, 108 inches wide across the top, 

 and 60 inches high. The water in the sluice was controlled by 

 half-moon gates (Fig. 102), located at the mouth of storage 

 reservoirs. 



TRESTLES 



Trestles may be built of round timber or of 2- by 6-inch or 

 4- by 8-inch sawed material. Flumes used for transporting sawed 

 material usually have a trestle made from square-edged material, 

 because it can be secured at the mill and transported to the place 

 of construction in the completed portion of the flume. Where 

 logs, pulp wood, acid wood, and other rough material are trans- 

 ported from the forest to the manufacturing plant, round timber 

 from 8 to 1 2 inches in diameter is often used for trestle construc- 

 tion for it can usually be secured in the vicinity, although some 

 prefer to erect a portable sawmill at the head of the flume and 

 manufacture lumber for its construction. 



Caps for round timber trestles are either made from small 

 timber hewed on opposite faces to the desired thickness or from 

 sawed material. Stringers are usually made from sawed timber. 

 The braces for round timber trestles are made from small 

 poles. 



For square-edged timber trestles caps are made from 2- by 6-, 

 4- by 4-, or 4- by 6-inch material, and stringers from 4- by 4-, 4- 

 by 6-, or 6- by 6-inch timbers, the choice depending on the size 

 of the box, the distance between trestle bents and the amount of 

 water carried. 



Braces for the box are placed along the stringers at 2-, 4-, or 

 8-foot intervals, depending on the length of the span, the form of 

 the box,^ and the strength required at special points, such as 



^ A V-box with a backbone for fluming lumber requires bracing only at 8-foot 

 intervals, while a box flume should have braces everj' 4 feet on a 24-foot span. 

 Loading points on log flumes are often braced at 2-foot intervals. 



