On equivalent roughness of mobile bed at high shear stress

0328720 - ÚH 2010 RIV SK eng J - Journal Article
Matoušek, Václav - Krupička, Jan
On equivalent roughness of mobile bed at high shear stress.
Journal of Hydrology and Hydromechanics. Roč. 57, č. 3 (2009), s. 191-199. ISSN 0042-790X. E-ISSN 1338-4333
R&D Projects: GA ČR GA103/06/0428
Institutional research plan: CEZ:AV0Z20600510
Keywords : bed shear * experiment * hydraulic transport * sediment transport
Subject RIV: BK - Fluid Dynamics
Impact factor: 1.000, year: 2009

The friction conditions at the top of a mobile bed are discussed for flows in the upper-plane-bed regime, i.e. for the flows with values of the bed Shields parameter larger than approximately 0.6. A special attention is devoted to flows of the bed Shields parameter bigger than 2. Experimental data for flows at high bed shear are collected from literature and new data are added from own measurements of flows of a 1.36-mm sand slurry in the 100-mm pipe loop of the Institute of Hydrodynamics. The paper analyses the data in order to evaluate a relationship among the equivalent roughness of the top of the bed and other relevant parameters. A semi-empirical formula is proposed that relates the equivalent roughness to the bed Shields parameter, the ratio of flow velocity and particle settling velocity, and the ratio of flow hydraulic radius and particle diameter. The formula is applicable primarily to flows of combined load (contact- and suspended loads together).
Permanent Link: http://hdl.handle.net/11104/0005431