Effect of Roughness on Discharge

  • T.W. Lau
  • N.R. Afshar


These Water resource projects and hydraulic engineering works have been developing rapidly throughout the world, thus prediction of water roughness coefficient is becoming an importance criteria for the designs of hydraulic related structure like open channel, and dam structure. The purposes of this research are to determine the effect of roughness on discharge and study on the factors that affect roughness coefficient. The roughness coefficient for this study is expressed in terms of Manning’s n. Experimental works were carried out to study the effect of roughness by using flumes (8m x 0.3m x 0.4m) with different types of roughened bed such as 2mm grain size plate and 5mm grain size plate. The experiments were being tested with various flow rates for slope equal to 1:300, 1:600 and 1:900 to determine the effect of slope on roughness coefficient. The results of the experimental study were presented and shown that the effect of surface roughness, material grain size, channel slope, and Manning’s roughness coefficient on flow rate. For the range of conditions tested, the discharge was found to be decreased as roughness coefficient increase. From the experiments, it shows smoother surface is having lower roughness coefficient and less retarding effect on the water flow, higher flow rate is produced. As conclusion, flow rate and roughness coefficient were influenced by bed roughness and slope.


H.R. French, "Hydraulic of Open Channel Flow", Washington: McGraw-Hill, 176-178,1966.

F. Huthoff, and D. Augustijin, "Channel roughness in 1D steady uniform flow: Manning or Chezy", Research for Managing Rivers: Present and Future Issues, 98-100, 2005.

V.T. Chow, "Open Channel Flow," London: McGRAW-HILL, 11,95,99,136-140,1959.

L.D. Donker, P. Troch, R. Verhoeven, K. Bal, P. Meire, and J. Quintelier, "Determination of the Manning Roughness Coefficient Influenced by Vegetation in the River", Environ Fluid Mech (2009) 9:549-567, 2009.


B.C. Yen, "Open Channel Flow Resistance", Journal of Hydraulic Engineering 128 (1): 20 - 39, 2002.


How to Cite
Lau, T., & Afshar, N. (2013). Effect of Roughness on Discharge. Journal of Civil Engineering, Science and Technology, 4(3), 29-33. https://doi.org/10.33736/jcest.124.2013