Sedimentary processes on an intertidal mudflat in the upper macrotidal Seine estuary, France |
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| Authors: | J Deloffre R Lafite P Lesueur S Lesourd R Verney L Guzennec |
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| Institution: | aUMR CNRS 6143, Morphodynamique continentale et côtière, Université de Rouen, 76821 Mont-Saint-Aignan Cedex, France;bUMR CNRS 6143, Morphodynamique continentale et côtière, Université de Caen, 14000 Caen Cedex, France;cUMR CNRS 8013 ELICO, Laboratoire de Biogéochimie et Environnement du Littoral, Université du Littoral-Côte d'Opale, 62930 Wimereux, France;dAgence de l'Eau Seine-Normandie, 76100 Rouen, France |
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| Abstract: | In order to understand the hydrodynamic parameters that control the fluvial sediment dynamics on an intertidal mudflat located in a sheltered zone in the upper part (fluvial part) of the macrotidal Seine estuary (France), a two-year field study of high-frequency field measurements was carried out. The bed-level evolution of the mudflat surface was measured from the semi-diurnal period to annual time scales using a high-resolution altimeter. The data showed that the sedimentary patterns on the mudflat were mainly controlled by river flows and tides. During high river flows in winter, sedimentation dominated; suspended particulate matter concentrations were higher, submersion was constant and at semi-diurnal scale, sedimentation duration was more important than erosion due to an asymmetrical tide. By contrast during low river flows in summer, erosion dominated mainly as a result of immersion/emersion of tidal flats during semi-diurnal cycle. From this annual sedimentation–erosion cycle we identify a temporary storage of 10–30% of the fine-grained (<63 μm) river-borne particles on mudflats in the upper section of the fluvial Seine estuary during high river flows.River-related sediment fluxes were estimated from the measurement of fine-grained sedimentation zones in the fluvial part of the estuary. The erosion/sedimentation processes were perennial, and the amounts of contributing sediments were directly related to the solid river load. Our results indicate that mudflats in the fluvial part of the Seine estuary play an important role in the downstream transfer of fine-grained suspended particulate matter (SPM) towards the turbidity maximum and the Rouen docks particularly during low river flows, when roughly 30–50% of the SPM originates from the eroded intertidal flats. |
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| Keywords: | fluvial estuary river flows intertidal mudflat morphology sediment transport erosion and deposition suspended particulate matter (SPM) Seine estuary |
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