UNITED STATES DEPARTMENT OF AGRICULTURE 
Contribution from the Bureau of Public Roads 
THOS. H. MACDONALD, Chief 
Washington, D. C. PROFESSIONAL PAPER June 7, 1920 
THE FLOW OF WATER IN DREDGED DRAINAGE 
DITCHES. 
THE RESULTS OF EXPERIMENTS TO DETERMINE THE ROUGHNESS 
COEFFICIENT, n, IN KUTTER’S FORMULA. 
By C. E. Ramser, Senior Drainage Engineer. 
CONTENTS. 
Page. Page. 
InfroducHonmereeyaseceen Sees ees se 1 | Description of experiments—Continued. 
Fiel@timeasu@ementses:2 02-0222. Jot Sselse2k: a2 Experiments in western Tennessee... -. 24 
Computations. se. c6 Sse 2 eet ae sas 4 Experiments in western lowa.........-- 36 
Talbubatesdscesultsme: ase a cee ee 6 Experiments in North Carolina.......... 45 
Deseripiionof chanmelsias* 2-5-2 =- oe we a Experiments in Florida................- 51 
AeCUnae yeCIteS Ulises ae ye eae See 9 Variation of n with stage..............-. 58 
Descriptron Of experiments .25-2--65 2250. = =: 9 Applicationsolmesultse..-.. 2252... seek 58 
Experiments in Lee County, Miss ....... DeleeConelusions A242 Sh oA Soe Le ea seeks = 59 
Experiments in Bolivar County, Miss... 17 
INTRODUCTION. 
Kutter’s formula is generally accepted by engineers as being the 
most satisfactory formula in use for computing the flow of water in 
open channels. After a thorough and unbiased study of all known 
formulas for computing the flow in open channels, engineers of the 
Miami Conservancy District conclude that “‘Although the Kutter 
formula is not ideal it is the best equation available at the present 
time.’ 1 The results obtained by the use of this formula are, how- 
ever, alfected to such a degree by the coefficient of roughness, n, that 
the selection of the correct value for this factor is a matter of the 
highest importance. The series of experiments described and sum- 
marized in the following pages were made for the purpose of deter- 
mining just what values of n properly apply to the various conditions 
of channel, and the endeavor has been made to present this informa- 
tion in the form that will be of the most practical value to engineers 
charged with the design of drainage channels or the computation of 
the discharge capacity of existing channels. 
1 The Maimi Conservancy District, Technical Reports, Part IV. ‘Calculation of Flow in Open 
Channels,” by Ivan E. Houk, Assoc. M. Am. Soc. C. E. 
146908°—20—Bull. 832 1 
