FLUMES AND THEIR STRUCTURE. 99 



nst simply on mudsills. Suitable drains and wings 

 must be provided at both ends of the flume. Where 

 Um-h flumes are constructed it is best to make the bench 

 twice as wide as the flume in order that there may be a 

 footway alongside. In such flumes the foundation is 

 simply mudsills and crossbeams. 



In sheathing a wooden flume it is best to use large 

 \viro nails or cut spikes for the floor, but the sides should 

 be fastened with bolts through inside cleats at the joints. 

 If nails are used in the side planking they will rot out 

 and it will be found impossible to keep the planks on. 



The weak spot in every flume is at either end where 

 the woodwork joins upon the earth or terreplein, as the 

 case may be. There the earth should be carefully pud- 

 dled at the apron and the whole surface from side to 

 side of the ditch, and the sides as well, should be tamped 

 and retamped. Retaining walls or riprap at the sides 

 and embracing the flaring wings may be employed, but 

 in any event the tamping must be thoroughly done and 

 the work gone over time and again if needs be in order 

 to prevent the possibility of washing out. This tamping 

 will be necessary if either the drop box or the inclined 

 apron be used. 



The bracing of a flume is an important matter, es- 

 pecially with deep flumes. A good system of side brac- 

 ing is depicted in the bridge flume across a stream, and 

 shown in Figure 30. 



Cross-section braces are often made with iron rods 

 running through the side posts and tightened with nuts 

 and washers. Any builder can arrange the matter of 

 the bracing to suit himself. 



In very high flumes a lofty trestle work may be re- 

 quired. If this is the case it is better to build the bents 

 in sections on the ground and then raise them into posi- 

 tion by means of tackle blocks and a windlass, or by using 

 a steam hoisting drum if the same may be readily ot>- 



