porous
and shattered material. Likewise where water is scarce and the
evaporation and absorption are great, flumes must necessarily be
preferred. In such cases as these either flumes or pipes may be
advantageously used.
Grades. —
Flumes are set, where practicable, on grades of twenty-five to
thirty-five feet per mile, and are consequently of proportionately
smaller area than ditches.
The annexed sketch shows the general stvle of constructing flumes.
Planking.—The planking
used ordinarily is of heart sugar pine (seasoned) one and one-half to
two inches thick, twelve to twenty-four inches wide, according to the
requirements, and twelve to sixteen feet long, the twelve-foot length
being the most desirable.
Sills and Posts. —Where
the boards join, pine battens three to four inches wide, one-half inch
thick, cover the seams Sills, posts, and caps strengthen the structure
every four feet. The dimensions of the timbers depend on the size of
the flume. A flume two and one-half feet square requires 3X4 inch
scantling for posts, caps, and sills, and 4X6 inch for the stringers ;
while a flume 4X3 feet in the clear should use 4X5 inch stuff for the
caps and posts, sills 4X6 inches, with stringers 10X8 inches in size.
These sizes are used in regions
