Sediment exchanges between the Seine estuary and its adjacent shelf

Abstract

The study of sediment dynamics within the Seine estuary and its adjacent shelf permits some conclusions regarding sediment exchanges in this coastal zone. On the shelf, sediment transport is directed toward the Seine estuary and contributes to the infilling of the estuary by marine sands and muds; these were originally derived from land carried to the shelf at times of lower sea level, and subsequently transported shoreward by dominant tidal and wave-induced currents. In the estuarine section, tidal processes form a turbidity maximum both by inducing strong bed resuspension and by trapping fluvial and marine sediments due to flood current predominance. Occasionally this turbid zone extends seaward during periods of river floods, and sediment is redispersed onto the shelf. This phenomenon has been amplified by man-made modifications of the estuarine morphology. However, currents patterns tend to retard the natural seaward escape of fluvial material, mainly due to dredging operations at the present time. Thus, man has changed the natural role of the estuary from a sink to a source of fluvial sediments for the shelf. A tentative sedimentary budget is proposed, taking into account the various sources of material and the complexity of sediment dynamics.

3D-numerical modelling of cohesive suspended sediment in the Western Scheldt estuary (The Netherlands)

“…However, these average values present more than 100% deviation from maximum and minimum values. According to the total average mud balance the estuary imports sediments from the sea, contrasting with other European estuary studies where the opposite occurs (AVOINE, 1986;DYER, 1986;VALE, 1990;RUCH et aL, 1993). Grain size distributions determined at 8 stations in the Western Scheldt (VINCX et aL, 1993), located at Waarde, Bath (Fig.l), Zandvliet and Lillo (located approximately 6 and 10 km, respectively, upstream of Bath), shows that in each cross section subtidal stations always have coarser sediments than intertidal stations.…”

Holocene and modern sediments in the Seine estuary (France): a synthesis

“…Upstream from Tancarville, data about the distribution of superficial sediments was provided by a small number of samples (Germaneau, 1971). Sedimentological relationships and interactions between the estuary and the Bay of the Seine were finally updated during the 1980s (Avoine, 1987;Avoine and Larsonneur, 1987). From 1993 to 1999, during the Seine-Aval Programme, the present-day sedimentary cover was identified or revised in relation to the entire system, including the upper estuary, 120 km upfrom the estuary mouth.…”

“…Instantaneous daily flows have a large range, from 150 m 3 s −1 during low river flows in summer, to 2300 m 3 s −1 during extreme river flows (unpublished data, Service de Navigation du Port de Rouen). The River Seine supplies a large amount of suspended silt and clay to its estuary and to the shelf (about 0.5 10 6 t yr −1 , Avoine, 1987).…”

“…5). Temporary mud sheets that occur at the bottom of the navigation channel are a recent feature, as the sediments were clean fine sands during the early 1980s (Avoine, 1987).…”

“…4). Here, siltation of heterogeneous medium sands is a result of the effects of the estuarine turbid plume: fine-grained supplies occur during the seaward escape of SPM from the estuary, mainly during high river flows and spring ebb tides (Avoine, 1987). This area is also under the control of tidal currents that winnow and disperse a part of the dredged spoils of Le Havre harbour (Fig.…”