50 BULLETIN 194, U. S. DEPARTMENT OF AGEICULTURE. 



proofing material that iiardens in tapering drops, is also liable to 

 come in this type. For type I except that unsurfaced lumber is used, 



lY. 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. 



y, 71 = 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 wiU 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,^ 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. 71 = 0.015 for flumes of group 2, in favorable alignment and 

 clean. 



III. 71 = 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 

 possibiUty of debris accumulations exists it should be considered in 

 design. 



1 Colorado Sta. Bui. 194. 



