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SUSPENDED SEDIMENT CONCENTRATIONS AND FLUXES OF A MEANDERING SYSTEM, THE ST. GEORGE DISTRIBUTARY,DANUBE DELTA

Laura Tiron Duţu, Florin Duțu, Gabriela Vlad, Iulian Pojar, Naliana Lupașcu

Abstract

Most of the suspension matter transported by rivers derives from the riverbed erosion. Complementary, the anthropogenic factor is responsible for the introduction of significant amounts of sedimentary material, especially suspended, but also dissolved material. In most cases, the distinction between naturally occurring materials and anthropic ones is almost impossible to achieve due to the complexity of the erosion processes. The suspended sediments concentration (SSC) and discharges were analyzed in the Danube Delta, along the St. George branch, which is highly sinuous and still morphologically dynamic. Along the St. George distributary, the cutoff of the natural channel by navigational canals between 1984 and 1988 caused dramatic changes in the local distribution of river ?ow velocities, discharge, and sediment ?uxes. The local variation of the concentration values of the SSC on the St George branch is related to the liquid flow, but also to other local factors, such as lithology, precipitation regime and periodically high flow debits due to the snow melting in the Danube drainage basin, as well as the discharge of rich-in-suspensions wastewater and other-like anthropogenic factors. In this study, attention will be focused on the evaluation of the suspended sediments and suspended sediment flows. Intensively affected by the anthropic pressures (e.g. embankment, meanders rectification), the SSC distribution along the St. George branch is disturbed by the presence of the artificial canals of the natural meander courses. Suspended sediment concentrations measured on the water samples on the the investigated sections (in a field campaign in September 2020) had mean SSC values per section between 7 and 36 mg·l-1. The distribution of SSC varies with every investigated section, depending on the local morphology. The St. George branch loses alluvial material load along its course by progressive sedimentation of the cutoff meanders and laterally through channels, canals, and over?ow.

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DOI resolver: doi.org/10.5593/sgem2021/3.1/s12.42

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