The Influence of Bed Roughness on Turbulence: Cabras Lagoon, Sardinia, Italy

Journal of Marine Science and Engineering

Clémentine Chirol⁴  Carl L. Amos⁴  Hachem Kassem⁴  Alice Lefebvre¹  Georg Umgiesser²  Andrea Cucco³ 

[1]MARUM Centre for Marine Environmental Sciences, University of Bremen, Bremen D-28334, Germany

[2] E-Mail:

[3]Institute of Marine Science ISMAR, National Research Council, Lanusei (OG) 08045, Italy

[4] E-Mail:

[5]Institute for coastal marine environment (IAMC), National Research Council, Oristano (IT) 09170, Italy

[6] E-Mail:

[7]Ocean and Earth Sciences Department, National Oceanography Centre Southampton, Southampton SO14 3ZH, UK

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关键词: turbulence;    bed roughness;    small-scale topography;    roughness length;    Law of the Wall;   

DOI  :  10.3390/jmse3030935

来源: mdpi

【 摘 要 】

Estimates of bed roughness used for predictions of sediment transport are usually derived either from simple scalars of the physical roughness (i.e., ripple height or grain size) or from the hydrodynamic roughness length (Zo) based upon velocity gradient estimates in the benthic boundary layer. Neither parameter accounts for irregular bed features. This study re-evaluates the relation between hydrodynamic roughness and physical bed roughness using high-resolution seabed scanning in the inlet of a shallow lagoon. The statistically-robust relationship, based on a 1D statistical analysis of the seabed elevation at different locations of the Cabras lagoon. Sardinia, has been obtained between Zo and the topographical bed roughness Ks by defining Ks = 2*STD + skin friction, with STD the standard deviation of the seabed elevation variations. This correlation between Ks and Zo demonstrates that the roughness length is directly influenced by irregular bed features, and that the Reynolds number accounts for the total drag of the bed: the data points collapse on the Law of the Wall curves with a fitting factor x = 0.5. Further testing must be done in other locations and in the fully-rough domain in order to test how widely those new parameters can be applied.

【 授权许可】

CC BY   
© 2015 by the authors; licensee MDPI, Basel, Switzerland.