4 BULLETIN 194^ U. S. DEPARTMENT OF AGEICULTURE. 



NECESSARY FIELD DATA FOR VALUES OF n. 



The labors of Kuttej and his colleague were devoced 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.^ 



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 hydrauhc 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, 



in 

 let B = k + , where k is 41 .66 and mis 0.00281 , and let e = 1 .811 , while 



V 



C is the Chezy coefiicient, equal to /^— • 



Then in formula 3, page 3. 



n- 



WUW^^IC^)^ 



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 



A 



matters of office computation. The hydrauhc 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 do, dj, dj, 



1 p. J. Flynn. Irrigation Canals and Other Irrigation Works. San Francisco, 1892. 



Samuel Fortier. Conveyance of Water in Irrigation Canals, Flumes, and Pipes. U. 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. 



U. 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. 



