2 BULLETIN 832, U. S. DEPARTMENT OF AGRICULTURE. 
The term 7 in Kutter’s formula is a measure of all the conditions 
in a channel that tend to retard the flow. 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 débris 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 m 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 n 
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. eis 
FIELD MEASUREMENTS. 
DISCHARGE. 
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. Acable 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 with a small Price current meter. 
These measurements were made at intervals of 24 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 
