Author(s): Leszek M. Kaczmarek; Malgorzata Robakiewicz; Lukasz Sobczak; Jaroslaw Biegowski
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Keywords: Graded sediment; Sorting; Concentration; Sheet flow; Modelling; Field measurements
Abstract: The present study is focused on the problem of vertical structure of sand concentration, vertical mixing and sorting both for river flow conditions and coastal zones. The problem is studied both theoretically and experimentally. The collected in situ data cover the Vistula river reach of about 6 km, while the coastal field data were obtained at the IBW PAN Coastal Research Station in Lubiatowo (Poland). In both experiments, the registrations of concentrations and grain size distributions of suspended sediment were carried out using the Particle Size Analyser LISST-100. The mathematical method for the continuous description of processes from the immobile bed to the formation of sheet-flow and suspended load is presented. The way of modelling of sediment–flow interactions is proposed, in which the near-bed flow is divided into three layers: the bedload layer, the contact load layer and outer flow region. In the present study the three-layer sediment transport system derived previously for non-graded situations is extended to graded sediments. In the domain of vertical sorting of grains in the coastal zone, the comparisons between the experimental data and the modelled concentrations yield satisfactory agreements. It can be concluded that nearly all sorting takes place during the pick-up process close to the bed, inside the contact load layer. In the outer layer, the grain size distribution remains fairly constant.
Year: 2004