Caractérisation des forçages contrôlant les flux sédimentaires longitudinaux et transversaux dans la zone de surf en domaine macrotidal

International audienc

Variation in longshore sediment transport under low to moderate energy conditions on barred macrotidal beaches.

The aim of this study was to estimate longshore sediment transport on three sandy barred macrotidal beaches of Northern France using sediment traps. Measurements of longshore sediment transport were carried out at several locations across the intertidal zone during rising and falling tides in order to obtain estimates of longshore sediment flux from the lower to the upper beach and coupled with high-frequency (2 Hz) hydrodynamic data using a series of hydrodynamic instruments. Results showed that longshore sediment transport increased with both wave height and mean flow, but no relation was found with wave angle which is probably due to the influence of tidal currents that interact with wave-induced longshore currents. Although, limited variation of longshore sediment transport was observed, cross-shore variation showed that sediment fluxes were higher on the middle to lower beach, which can be explained by a decrease in tidal flow velocity towards the upper beach as well as wave-energy dissipation over the beach and intertidal bars. Longshore sediment transport direction appeared to be controlled by both incoming wave and tidal current direction, depending on the hydrodynamic zones, sediment transport being tidally-dominated in the shoaling zone and mostly wave-induced in the inner surf zon

Estimation of longshore and cross shore sediment transport on sandy macrotidal beaches of northern France. Coastal Sediments '11, 7th Int. Symp

International audienceIn this paper, data on longshore and cross-shore sediment transport were obtained during six field experiments, on three sandy macrotidal barred beaches of northern France. This study is based on sediment trap experiments, following the method of Kraus (1987), and completed by wave and current measurements using a series of hydrodynamic instruments deployed across the intertidal zone. Results showed that longshore sediment transport increased with both wave height and mean flow, but no relation was found with wave angle which is probably due to the influence of tidal currents that interact with wave-induced longshore currents. Cross-shore sediment flux was generally higher than longshore flux, suggesting that shore-perpendicular sediment transport associated with wave oscillatory currents probably represents a major factor controlling the cross-shore migration of intertidal bar

Chronostratigraphy and spatial distribution of magnetic sediments in the Chukchi and Beaufort seas since the last deglaciation

Palaeomagnetic investigation of three sediment cores from the Chukchi and Beaufort Sea margins was performed to better constrain the regional chronostratigraphy and to gain insights into sediment magnetic properties at the North American Arctic margin during the Holocene and the preceding deglaciation. Palaeomagnetic analyses reveal that the sediments under study are characterized by low‐coercivity ferrimagnetic minerals (magnetite), mostly in the pseudo‐single domain grain‐size range, and by a strong, stable, well‐defined remanent magnetization (MAD <5°). Age models for these sediment cores were constrained by comparing their palaeomagnetic secular variations (inclination, declination and relative palaeointensity) with previously published and independently dated sedimentary marine records from the study area. The magnetostratigraphical age models were verified by AMS radiocarbon dating tie points, tephrochronology and 210Pb‐based sedimentation rate estimate. The analysed cores 01JPC, 03PC and 02PC span c. 6000, 10 500 and 13 500 cal. a BP, respectively. The estimated sedimentation rates were stable and relatively high since the deglaciation in cores 01JPC (60 cm ka−1) and 03PC (40–70 cm ka−1). Core 02PC shows much lower Holocene sedimentation rates with a strong decrease after the deglaciation from ~60 to 10–20 cm ka−1. Overall, this study illustrates the usefulness of palaeomagnetism to improve the dating of late Quaternary sedimentary records in the Arctic Ocean

Modélisation de l’impact du changement climatique sur l’érosion des dunes. Application à la Camargue

Three climatic changes scenariis were investigated by an increase of energy and by the duration of an extreme storm. The wave caracteristics properties and the sea level time series of the referenced storm were increased of about 5, 10 and 20 % in order to define the dune erosion. We evidenced that the wave height displays more influence on the dune erosion than the sea level. Moreover, the storm duration, over 4 days, does not play an important role on the dune erosion. However, there is no proportional relationships between a weak storm energy increase and/or duration, and dune erosion. A small increase of storm will have a large impact on dune erosion in the future.