14 BULLETIN 87, U. S. DEPARTMENT OF AGRICULTURE. 
reliable survey, however, is absolutely necessary, and a carefully 
constructed profile map highly desirable before construction begins. 
The cost of the completed survey would be comparable to that of a 
branch railway location. 
The blasting out of rocks and bowlders or projecting points of 
bluffs is sometimes advisable and necessary in order to reduce curva- 
ture and allow the flume to run in as direct a line as possible. This 
reduces the danger of " jamming " and makes it possible to handle 
longer material without its "binding" as a result of the ends "press- 
ing" against the lining of the flume on the outside of the curve 
while the middle of the stick presses against the lining on the inside. 
Just what is necessary to be done in this respect can best be calculated 
by using a carefully prepared profile map made from an actual sur- 
vey of the proposed flume line. 
The matter of grade in flume construction is one of great impor- 
tance. It is not always possible to vary the location so as to maintain 
an equable or steady, even grade in all portions of a flume line, but 
wherever it can be accomplished without incurring too great an 
expense it should always be done. Flume operators have found 
the question of satisfactory grade to be one of the most important 
features of successfully fluming material, since where there is a 
stretch of comparatively flat grade the supply of water may be 
ample to nearly fill the flume, but upon arrival at a point in the 
flume line where the descent is very abrupt, the accelerated speed 
of the water reduces its volume to a small amount in the bottom 
of the flume and, consequently, results in the flumed material "rub- 
bing" or "sliding" down the descent for a long distance on the sides 
of the V. Such action wears out the hning very rapidly, necessitates 
its being frequently renewed, and produces a dangerous condition 
through the liability of the material to jam and pile up, and either 
be thrown out of the flume or break it down as a result of the in- 
creased weight. t 
In general, the lowest grade that is considered satisfactory for 
successful operation is approximately 1 per cent, or 1 foot in 100 
feet, but it is better to maintain a grade of from 2 to 5 per cent 
when possible. The maximum grade that can be used runs up 
to a very high pitch; some flumes have been successfully operated 
for a short distance at a grade of 30°, but such a steep grade is 
very undesirable, as it is usually impossible to maintian a sufficient 
volume of water in the flume. The most satisfactory results in flum- 
ing will be obtained at from 2 to 10 per cent grade, and it should be 
held below 15 per cent whenever possible. 
