4 BULLETIN 194, TJ. S. DEPARTMENT OF AGRICULTURE. 
NECESSARY FIELD DATA FOR VALUES OF n. 
The labors of Kutter and his colleague were devoted to the develop- 
ment of a formula from the field experience of other engineers. 
Taking his formula as a basis, the later authors have made deductions 
from the tests of their predecessors and such experiments as they 
themselves conducted. 1 
The tests of any one experimenter have for the most part been 
confined to one part of the country, and each one has secured the 
necessary field data by methods differing more or less from those 
pursued by the others. The hydraulic elements to be determined in 
the field are, however, essentially the same. 
As previously stated, n is the one factor not easily and assuredly 
determined in office estimates of canal design. Therefore the field 
data must be secured with a view to solving the equation in Kutter's 
formula, with the value of n as the desired answer. 
For the sake of brevity in computation, in formula 3, on page 3, 
let B = k + m , where k is 41 .66 and m is 0.00281 , and let e = 1 .81 1 , while 
s ' 7 
V 
C is the Chezy coefficient, equal to /-p— . 
Then in formula 3, page 3. 
None of the variables entering the solution of this equation are 
directly obtained in the field, although computed from field measure- 
ments. The mean area, A, and the mean wetted perimeter, P, are 
matters of office computation. The hydraulic radius, R, equals p- 
In the field the length of reach chosen is divided into several equal 
parts, the more the better. At the ends of the reach and at the 
dividing planes of the various parts sufficient soundings are made at 
measured distances apart, so that the cross-sectional area may be 
found. 
Beginning at one bank of the canal, assume the soundings to be 
made the same distance apart, x, and calling the soundings d , d„ d 2 , 
i P. J. Flynn. Irrigation Canals and Other Irrigation Works. San Francisco, 1892. 
Samuel Fortier. Conveyance of Water in Irrigation Canals, Flumes, and Pipes. TJ. S. Geol. Survey, 
Water-Supply and Irrig. Paper 43 (1901). 
C C. Williams. Notes on the Flow of Water in Irrigation Ditches. Univ. Colo. Studies, 7 (1910), No. 4, 
p. 237. 
TJ. S. Reclamation Service, Reclamation Rec, 4 (1913), No. 7. 
V. M. Cone, R. E. Trimble, and P. S. Jones. Frictional Resistance in Artificial Waterways. Colorado 
Sta. Bui. 194 (1914). 
J. B. Lippincott. Observations to Determine the Value of C and n as Used in the Kutter Formula. 
Engin. News, 57 (1907), No. 23, p. 612. 
