50 BULLETIN 194, U. S. DEPARTMENT OF AGRICULTURE. 
proofing material that hardens in tapering drops, is also liable to 
come in this type. For type I except that unsurfaced lumber is used. 
IV. 71 = 0.015 for flumes of unplaned lumber, but otherwise as of 
type II. In the opinion of the writer this is about the value to use 
for the usual grade of construction in a mountain canyon where the 
flume will get about the usual grade of maintenance with repairs 
made with irregular-shaped scraps of boards. 
V. 7i = 0.016 for flumes of type IV where sharp bends rather than 
curves are installed. For flumes lined with rough roofing material 
and for the ordinary grade of construction on a flume that is built 
and generally left to care for itself. The kind of an organization that 
is to operate the flume will determine this factor. 
For values of n higher than 0.016 the inside of a flume has changed 
so that its character as a wooden flume is practically lost. Debris 
accumulations, warped and loose battens, excessive sagging, with 
consequent accumulation of debris, all contribute to make values 
above 0.016 rather indeterminate, except by actual test. 
VALUES OF n FOR METAL FLUMES. 
As noted in a bulletin of the Colorado Agricultural Experiment 
Station, 1 metal flumes are divided into three clean-cut groups. 
Group 1. Those having countersunk joints between the various 
sheets of metal so that there is practically no added roughness pre- 
sented to the water. 
Group 2. Those having joints that project into the water section 
presenting a shoulder every few feet that effectually retards the 
velocity. This type is not installed to any great extent at present, 
but there is a great deal of it in actual use, as it was the pioneer in 
steel fluming. * 
Group 3. Those having regular corrugations at right angles to the 
axis of the flume. This makes a stiff flume, not so liable to sag, but 
with a rather high value of n. 
I. 71 = 0.011 for flumes of group 1, in favorable alignment and clean. 
II. 7i = 0.015 for flumes of group 2, in favorable alignment and 
clean. 
III. 7i = 0.022 for flumes of group 3, in favorable alignment and 
clean. 
This value is based on but one observation, by Mr. Cone. 
Where flumes are short, they are liable to accumulate the same class 
of detritus in the bottom as the section above them. Where the 
possibility of debris accumulations exists it should be considered in 
design. 
i Colorado Sta. Bui. 194. 
