FLUMES AND FLUMING. 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 
unevenness 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 hes — 
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. 
CURVES. 
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- 
