2 BULLETIN 832, U. S. DEPARTMENT OE AGRICULTURE. 



The term n in Kutter's formula is a measure of all the conditions 

 in a channel that tend to retard the Sow. It is quite often regarded 

 as simply a measure of the friction between the flowing water and the 

 material forming the perimeter, all other conditions in the channel 

 being disregarded. Some of the conditions that influence the value 

 of n for earth channels are irregularities in the wetted perimeter, 

 nonuniformity of cross section in size and shape, the growth of vege- 

 tation in the channel, such as grass, weeds, roots, vines, bushes and 

 trees, and the presence of other obstructions to flow, such as logs, 

 stumps, drift, and debris of all kinds. Various combinations of these 

 conditions that may exist in a channel make it difficult to choose the 

 proper value of n in computing the flow of an open channel or the 

 probable flow for proposed artificial channels. The engineer who 

 has had a wide personal observation of conditions in channels for 

 which values of n have been determined is generally well qualified to 

 choose the proper values of n in the design of channels. On the other 

 hand, the engineer who has not had similar experience must depend 

 for his choice of n upon views and descriptions of channels for which 

 values of n have been determined by experiment. In this paper 

 views and careful descriptions of the channels for which values of re 

 were determined are presented as being the best method of making 

 the results of practical application. 



The experiments described were conducted in six different locali- 

 ties, namely. Lee County, Miss.; Bolivar County, Miss.; western 

 Tennessee; western Iowa; southern North Carolina; and eastern 

 Florida. The first four sets of experiments were made by the author. 

 The experiments conducted in North Carolina and Florida were made 

 by A. D. Morehouse and F. E. Staebner, respectively, both drainage 

 engineers of the Bureau of Public Roads. All of these experiments 

 were conducted under the direction of S. H. McCrory, chief of drainage 



investigations. 



FIELD MEASUREMENTS. 



Q13CHA 



Particular care was taken to secure accurate discharge measure- 

 ments. With few exceptions the gauging stations were located on single 

 span bridges, so that there was no interference with the natural flow 

 of the water. Where suitable existing bridges at desirable sections 

 could not be found, suspension footbridges were constructed, one of 

 which is shown in Plate I, figure 1. A cable gauging station was built 

 on the Bogue Phalia channel in Bolivar County, Miss. (See Plate I, 

 fig. 2.) Where the cable stations and suspension bridges were built 

 ideal gauging sections were obtained. 



Velocity measurements were made witn a small Price current meter. 

 These measurements were made at intervals of 2\ feet across the 

 streams for the smallest channels, 5 feet for the medium-sized chan- 

 nels, and 10 feet for the largest channels. At the measuring points 



