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Effect of bed surface roughness on longitudinal dispersion in artificial open channels
Author(s) -
Schulz Marcus,
Priegnitz Jan,
Klasmeier Jörg,
Heller Stefan,
Meinecke Stefan,
Feibicke Michael
Publication year - 2011
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/hyp.8229
Subject(s) - dispersion (optics) , surface roughness , surface finish , open channel flow , hydraulic roughness , mechanics , hydraulics , materials science , geology , flow (mathematics) , flow velocity , geotechnical engineering , hydrology (agriculture) , optics , composite material , thermodynamics , physics
In several empirical and modelling studies on river hydraulics, dispersion was negatively correlated to surface roughness. In this study, it was aimed to investigate the influence of surface roughness on longitudinal dispersion under controlled conditions. In artificial flow channels with a length of 104 m, tracer experiments with variations in channel bed material were performed. By use of measured tracer breakthrough curves, average flow velocity, mean longitudinal dispersion, and mean longitudinal dispersivity were calculated. Longitudinal dispersion coefficients ranged from 0·018 m 2 s −1 in channels with smooth bed surface up to 0·209 m 2 s −1 in channels with coarse gravel as bed material. Longitudinal dispersion was linearly related to mean flow velocity. Accordingly, longitudinal dispersivities ranged between 0·152 ± 0·017 m in channels with smooth bed surface and 0·584 ± 0·015 m in identical channels with a coarse gravel substrate. Grain size and surface roughness of the channel bed were found to correlate positively to longitudinal dispersion. This finding contradicts several existing relations between surface roughness and dispersion. Future studies should include further variation in surface roughness to derive a better‐founded empirical equation forecasting longitudinal dispersion from surface roughness. Copyright © 2011 John Wiley & Sons, Ltd.