of heavy snow, and can be reduced somewhat in milder localities.
The
width of the flume regulates the length of the sills and caps, and the
length of the posts is determined by the depth of the flume, three
inches or less being allowed between the top of the planks and the cap.
In larger flumes these different sizes are slightly increased.
The
posts should be set into the caps and sills with a gain of one and
one-fourth inch, and not mortised. The sills generally extend from
twelve to twenty inches beyond the post (according to the size of the
structure), and to them side braces are nailed to strengthen the
structure, although these side braces are generally unnecessary in
properly constructed flumes. In the mountain regions snow and ice
frequently attach themselves to the braces and sills, breaking them off
and occasionally destroying the flume. On top of the caps there is
placed a foot plank eight to ten inches in width.
Flumes
should be placed on a solid bed on the required grade. To avoid damage
from slides, or snow and wind storms, the bed should be excavated in
the bank of the side hills and the flume placed close to the bank.
Stringers running the entire length of the flume are placed beneath the
sills immediately outside of the posts. They are not absolutely
necessary, but are desirable, as they preserve the sill timbers from
decay.
Curves.—When
curves are necessary they should be laid with great care, so as to
insure the maximum flow of water. The boxes must be cut in two, three,
or four parts, as the case may demand. This necessitates an increase
in the number of sills, posts, and caps. To secure the better curving
of the side planks they are sawed partially through in different
places, so that they bend easily, the sawed portions closing thoroughly
by the curving of the plank.
To distribute the water equally over the entire flume and prevent slack water, irregular currents, and splash-
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