Parameterisation of clastic sediments including benthic structures

Bobertz, B., Harff, J. and Bohling, Bjoern (2009) Parameterisation of clastic sediments including benthic structures Journal of Marine Systems, 75 (3-4). pp. 371-381. DOI 10.1016/j.jmarsys.2007.06.010.

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The sediment transport processes in the south-western Baltic Sea are predicted by means of a numerical model in the project DYNAS. There are two sediment parameters that influence the results of modelling remarkably: critical shear stress velocity and bottom roughness. This paper presents the way how to parameterise these factors and extrapolate them into the investigation area. The critical shear stress velocity is parameterised basing on grain size data, combining approximations after Hjulstrom [Hjulstrom, F., 1935: Studies in the morphological activity of rivers as illustrated by the river Fyris. Geological Institution of University of Uppsala: Bulletin (25): 221-528.], Shields [Shields, A., 1936: Anwendung der Ahnlichkeits-Mechanik and der Turbulenzforschung auf die Geschiebebewegung. Mitteilungen der Preussischen Versuchsanstalt fur Wasserbau and Schiffahrt (26): 26 pp.] and Bohling [Bohling, B., 2003: Untersuchungen zur Mobilitat naturlicher and anthropogener Sedimente in der Mecklenburger Bucht. unpublished doctoral thesis, Mathematisch-Naturwissenschaftliche Fakultat, Ernst-Moritz-Amdt-Universitat Greifswald/Germany,156 pp.]. The roughness length, in the case of absence of macro zoo-benthos and their structures, is parameterised basing on grain size too employing Soulsby [Soulsby, R.L, 1997: Dynamics of Marine Sands: a Manual for Practical Applications. London, Thomas Telford Publications. 249 pp.], Nielsen [Nielsen, P.,1983: Analytical determination of nearshore wave height variation due to refraction shoaling and friction. Coastal Engineering 7, 233-251.] and Yalin [Yalin, M.S.,1977: Mechanics of Sediment Transport. Pergamon Press, New York. 298 pp.]. No equivalent simple parameterisations for biologically caused bed roughness exist. Here, findings of Friedrichs [Friedrichs, M., 2004: Flow-induced effects of macro zoo-benthic structures on the near-bed sediment transport. Dissertation, Universitat Rostock, 80 S.] and estimations by the DYNAS biologists group were combined in order to derive roughness lengths from abundance measurements of four previously selected key species which represent the originators of the dominating benthic structures at the sea floor in the south-western Baltic Sea. Critical shear stress velocity and bed roughness are known at few sample sites only. They were extrapolated into the larger investigation area using a proxy-target concept. The mean near bottom milieu (bathymetry, median grain size, salinity, oxygen) which was derived using results from numerical modelling serves as the proxy. Since the milieu parameters are measured at the sampling sites for which the target parameters have been determined, a combined hierarchical and supervised classification was employed to transfer the local knowledge into the unknown investigation area. (C) 2008 Elsevier B.V. All rights reserved.

Document Type: Article
Keywords: Sediment dynamics Mathematical models Parameterisation Benthos Bed roughness Critical shear stress Europe Baltic Sea Mecklenburg Bight 10 degrees E/53 degrees N-15 degrees E/56 degrees N western baltic sea incipient motion tidal currents threshold classification erosion flows transport movement waters
Research affiliation: Kiel University
DOI etc.: 10.1016/j.jmarsys.2007.06.010
ISSN: 0924-7963
Date Deposited: 22 Dec 2011 05:04
Last Modified: 08 Oct 2012 10:09

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