FLUMES AND FLUMIZSTG. 15 



TRESTLING. 



In maintaining the steady or even grade of a flume it is nearly 

 always necessary to do more or less "trestling," in order to avoid 

 mievenness in the line, reduce distance and abrupt curvature, and 

 hold the general grade of the flume at the desired height. (PL I.) 

 Here, again, the necessity of a careful survey becomes apparent, for 

 without a knowledge of just what the height of the trestling needs 

 to be in each successive 12 to 16 foot distance, it would be impossible 

 to know just what length the bents and braces of the trestling should 

 be cut, or just what "pitch" should be given to the bracing legs of the 

 trestle, or just where the foundation "stepping" should be placed 

 in order to hold the top of the flume firmly in the desired position. 



I can not make the question of the necessity of a careful survey 

 too important, especially for a mountainous or rough and rugged 

 country, which is the type of locality in which considerable trestling 

 is most likely to be used. In this connection, it is sometimes very 

 advisable in the interest of economy, and necessary from the view- 

 point of successful operation, to grade out the earth along the sides 

 of ridges, where this can be done cheaper than trestling can be con- 

 structed in other localities along the line, for its effect in maintaining 

 the desired grade. Also, grading out is in some cases desirable in 

 order that the top of the flume, when completed, may be practically 

 on a level or a little below the earth's surface, at least on one side, 

 so that logs or heavy timber to be shipped may be "loaded" into the 

 flume without having to use a needless amount of energy to get them 

 there. 



In many cases the amount of money spent in loading he?~ 

 terial into a flume set up unnecessarily high above the earth's sur- 

 face has eventually cost the operator much more than it would to havp* 

 lowered his flume by grading or slightly changing its course in the 

 first place. This is a feature that should not be overlooked. 



In the location of a flume line it is advisable to avoid abrupt curva- 

 ture as much as possible. Where the contour of the country makes 

 curves or bends in a flume necessary, they should, whenever possible, 

 be on long, even lines. (See PI. II.) A sharp curve in a flume 

 throws the weight of the material and the water by centrifugal force 

 to the outside of the curve, and the abrupt bend in the flume has a 

 tendency to dam up or hold back the water. The material is thus 

 much more liable to jam or block on an abrupt curve than on a grad- 

 ual one. When a jam occurs in the flume the blocked material acts 

 as a dam, and after several sticks or pieces of lumber have stopped, 

 the front end of the block or jam rests solidly on the sides and bot- 



