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The effect of sediment concentration on bedload roughness
Author(s) -
Bergeron Normand E.,
Carbonneau Patrice
Publication year - 1999
Publication title -
hydrological processes
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.222
H-Index - 161
eISSN - 1099-1085
pISSN - 0885-6087
DOI - 10.1002/(sici)1099-1085(199911)13:16<2583::aid-hyp939>3.0.co;2-s
Subject(s) - bed load , flume , hyperconcentrated flow , hydraulic roughness , sediment , geology , flow velocity , surface finish , geotechnical engineering , bedform , sediment transport , shear velocity , flow (mathematics) , flow conditions , hydrology (agriculture) , surface roughness , geomorphology , mechanics , materials science , turbulence , composite material , physics
Bedload roughness is the roughness produced by sediment transported near the bed. While it is well established that the magnitude of this roughness is proportional to the thickness of the moving sediment layer, the effect of sediment concentration remains largely unknown. This paper presents the results of a flume experiment that was designed to investigate the effect of sediment concentration on bedload roughness. The experiment consisted of creating flow conditions where bedload transport is supply‐limited and injecting gravel size particles (D 50 =7·4 mm) at the upstream end of the flume in order to produce bedload transport. While keeping flow conditions constant, sediment concentration was varied by successively increasing the injection rate of gravel in the flow. For each injection rate, flow velocity profiles were measured in order to evaluate changes of mean flow velocity U , shear velocity u * , roughness length z o and resistance to flow f . The results indicate that low sediment concentration affects mainly the near bed portion of the flow where it causes a reduction of mean flow velocity and an increase of shear velocity and roughness length. For larger sediment concentration, the whole flow velocity profile becomes affected by bedload roughness but the importance of this effect always remain larger near the bed. As sediment concentration is augmented, mean flow velocity is consistently reduced but shear velocity and roughness length increase until a plateau is reached where these two variables become constant. Copyright © 1999 John Wiley & Sons, Ltd.