Syracuse

Archive ouverte | Oceanolica Acta (0399-1784) (Gauthier-Villars), 1997 , Vol. 20 , N. 6 , P. 811-822

Levoy, F | Monfort, O | Larsonneur, C

Edité par Gauthier-Villars

Fluorescent tracers, often used to study longshore transports induced in the breaking zone, are here adapted to the multidirectional movements observed on macrotidal beaches, where sediment transports are dominated by wave or tide action or by the simultaneous action of both. The relative influences of these agents vary in space and time. Different techniques of quantifying fluorescent grain concentrations, by surficial or volumetric counting of samples are tested and compared. The automatic counting of fluorescent grains present in the mobile layer is also tested and validated. Comparisons, made during a preliminary experiment, between concentrations evaluated in this manner and values inferred from visual inventories are satisfactory. The different methods make it possible to take the granulometric heterogeneity of the sediment stock into account. The technique is then applied to the western coast of Cotentin. The relative influence of waves and tidal currents on sediment mobility is studied for two contrasted hydrometeorological climates at different points on a macrotidal beach. Wave action on sediment movement intensity and direction is predominant on the middle foreshore, where transport rates can reach 25 kg.m(-1)min(-1) during stormy conditions. On the lower foreshore, the action of waves, tidal currents or estuary dynamics depends on hydrodynamic conditions. The transport rates induced by mean current action do not exceed 0.2 kg.m(-1)min(-1). Values ten times larger can be observed under wind-wave action.

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