TECHNICAL NOTE / MANNING’S ROUGHNESS COEFFICIENT IN A TRAPEZOIDAL-SHAPED CHANNEL

B. ACHOUR, L. AMARA

Abstract


The study proposes to establish the relation which governs the Manning’s n roughness coefficient in a trapezoidal-shaped channel. It appears that n depends on the depth of the flow, the bottom width of the channel, the slope of the channel, the absolute roughness characterizing the state of the internal wall of the channel, the side slope, the acceleration due to gravity, and the kinematic viscosity of the flowing liquid. The coefficient n is therefore not constant for a given trapezoidal canal, the bottom width of which as well as the side slope are known. It does not depend solely on the material constituting the channel as suggested in the literature. Considering the cases of the smooth and rougher trapezoidal canal, with a given side slope, the curves of variation of n have been drawn. The defined shear Reynolds number as a function of the bottom width, the slope of the channel and the kinematic viscosity plays an important role in the variation of n up to a lower limit value of the relative roughness beyond which it has no longer influence. The rough turbulent flow regime is then achieved. For shallow depths, the coefficient n takes on large values, which is in mathematical accordance with Manning's equation.


Keywords


Manning’s coefficient, relative depth, trapezoidal-shaped channel, free surface flow, open channel flow.

Full Text:

PDF

References


ACHOUR B. (2014). Canal rectangulaire en charge et à surface libre, Chapitre II, Cours et exercices d’application, Pressurized and free surface flow rectangular channel, Chapter II, Application courses and exercises, Editions Al-Djazair, Algiers, In French, 63p.

ACHOUR B., AMARA L. (2020). Proper relationship of Manning’s Coefficient in a Partially Filled Circular Pipe, Larhyss Journal, No 42, pp.107-119.

ACHOUR B., BEDJAOUI A. (2006). Discussion to “Exact solution for normal depth problem, by SWAMME P.K. and RATHIE P.N., Journal of Hydraulic Research, Vol.44, Issue 5, pp.715-717.

ACPA (The American Concrete Pipe Association). (2000). Concrete Pipe Design Manual, 561p.

ACPA (The American Concrete Pipe Association). (2012). Manning’s n Values-History of Research, USA, 12p.

BARFUSS S., TULLIS J.P. (1989). Friction Factor Test on High Density Polyethylene Pipe, Hydraulic Report, No 208, Utah Water Research Hydraulic Report, Utah State University, Logan, Utah, USA.

CAMP T.R. (1946). Design of Sewers to Facilitate Flow, Sewage Works Journal, Vol.18, Issue 1, pp.3-16.

CHOW V.T. (1959). Open-channel Hydraulics, McGraw-Hill, New York, USA, 680p.

HENDERSON F. M. (1966). Open channel flow, MacMillan Publishing Co. Inc., New-York.

STREETER V.L. (1971). Fluid Mechanics, McGraw-Hill, USA, 751p.

U.S. Department of Transportation (2012). Hydraulic Design of Highway Culverts, Federal Highway Administration’s FHWA, 3rd Edition, Publication No FHWA-HIF-12-026, Hydraulic Design Series No 5, USA, 323p.

University of Minnesota (1950). Hydraulic Tests on Concrete Culvert Pipes, St. Anthony Falls Hydraulic Laboratory, Technical paper No 4, Series B, USA.


Refbacks

  • There are currently no refbacks.


Creative Commons License
This work is licensed under a Creative Commons Attribution 3.0 License.