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 fine 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 lining 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. 



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. 



