www.iaset.us editor@iaset.us SURFACE FRICTION IN OPEN CHANNEL BIRENDRA KUMAR SINGH & ANAND KUMAR SINHA Department of Civil Engineering, Birla Institute of Technology, Mesra, Ranchi, Jharkhand, India ABSTRACT Roughness depends upon size of the roughness material. Since D 50 are more for 2.5 inch roughness bed as compared to 2.0 inch roughness bed hence lesser value of 50 D d and 84 D d indicate more roughness. There is less size of 2.0 inch roughness bed which is not submerged as compared to 2.5 inch roughness bed and function of effective roughness concentration depends upon wetted frontal cross sectional area i.e. wetted frontal cross sectional area is more for 2.0 inch roughness bed hence function of effective roughness concentration is more for 2.0 inch roughness bed as compared to 2.5 inch roughness. Subject Headings: Boulders, Channels, Drag, Flow resistance, Flumes KEYWORDS: Friction Factor, Hydraulic Geometry, Roughness INTRODUCTION For large scale roughness 50 D d <2 and 84 D d <1.2 where d is the mean depth of flow and D 50 = the size of the median axis which is bigger than or equal to 50% of median axis. Similarly D 84 = The size of the median axis which is bigger than or equal to 84% of median axis. Similarly for Intermediate Scale roughness 2< 50 D d <7.5 and 1.2 < 84 D d <4. Hence both the roughness bed provide large scale roughness. Experimental Set up and Procedures: Data were obtained for 2.0 inch and 2.5 inch roughness bed. Flume: The flume is open and 1.168m wide and 9.54 m long. Each roughness bed was constructed by smearing masonite boards with fiberglass resin. The boards were then screwed to the bed of the flume. Experimental Procedure: For each bed, five to seven flows were measured for three different slopes (2,5 and 8%). At each flow, depth was gaged at a single cross section, so that mean flow and channel properties could be calculated. In flow with large- scale roughness, the cross- sectional area of flow is significantly affected by the projections of the elements into the flow. Table 1: Flume Data for 2.0 Inch Roughness Bed Sl. No. (1) Channel Slope (2) Discharge in Cubic Meters per Second (3) Mean Velocity in Meters per Second (4) Mean Depth d in Meters (5) 1 0.02 0.00329 0.100 0.0282 2 0.02 0.00837 0.189 0.0378 3 0.02 0.01158 0.227 0.0436 International Journal of Civil Engineering (IJCE) ISSN(P): 2278-9987; ISSN(E): 2278-9995 Vol. 3, Issue 3, May 2014, 39-54 © IASET