Tidal pumping, baroclinic circulation, and vertical mixing are known to be the main mechanisms responsible for the estuarine turbidity maximum (ETM) formation. However, the influence of hydro‐meteorological conditions on ETM dynamics is still not properly grasped and requires further investigation to be quantified. Based on a realistic three‐dimensional numerical model of the macrotidal Seine Estuary (France) that accounts for mud and sand transport processes, the objective of this study is to quantify the influence of the main forcing (river flow, tides, and waves) on the ETM location and mass changes. As expected, the ETM location is strongly modulated by semidiurnal tidal cycles and fortnightly time scales with a high sensitivity to river flow variations. The ETM mass is clearly driven by the tidal range, characteristic of the tidal pumping mechanism. However, it is not significantly affected by the river flow. Energetic wave conditions substantially influence the ETM mass by contributing up to 44% of the maximum mass observed during spring tides and by increasing the mass by a factor of 3 during mean tides compared to calm wave conditions. This means that neglecting wave forcing can result in significantly underestimating the ETM mass in estuarine environments. In addition, neap‐to‐spring phasing has a strong influence on ETM location and mass through a hysteresis response associated with the delay for tidal pumping and stratification to fully develop. Finally, simulations show that the uppermost limit of the Seine ETM location did not change notably during the last 35 years; however, the seaward limit migrated few kilometers upstream.

The modeling of tsunami generation is an essential phase in understanding tsunamis. For tsunamis generated by underwater earthquakes, it involves the modeling of the sea bottom motion as well as the resulting motion of the water above it. A comparison between various models for three-dimensional water motion, ranging from linear theory to fully nonlinear theory, is performed. It is found that for most events the linear theory is sufficient. However, in some cases, more sophisticated theories are needed. Moreover, it is shown that the passive approach in which the seafloor deformation is simply translated to the ocean surface is not always equivalent to the active approach in which the bottom motion is taken into account, even if the deformation is supposed to be instantaneous.

The computation of long wave propagation through the ocean obviously depends on the initial condition. When the waves are generated by a moving bottom, a traditional approach consists in translating the 'frozen' sea bed deformation to the free surface and propagating it. The present study shows the differences between the classical approach (passive generation) and the active generation where the bottom motion is included. The analytical solutions presented here exhibit some of the drawbacks of passive generation. The linearized solutions seem to be sufficient to consider the generation of water waves by a moving bottom. To cite this article: D. Dutykh et al., C. R. Acad. Sci. Paris, Ser. I 343 (2006). RésuméThéorie linéaire de génération de vagues par mouvement du fond. Les calculs de propagation d'ondes longues à travers l'océan doivent naturellement être alimentés par la condition initiale. Le but de cette note est de montrer l'insuffisance de l'approche classique qui consiste à translater la déformation « gelée » du fond vers la surface libre et à la laisser se propager. Un calcul analytique qui met en évidence les inconvénients de l'approche classique de génération passive est présenté ici. Les solutions linéa-risées semblent être bien adaptées pour traiter la génération de vagues par mouvement du fond. Pour citer cet article : D. Dutykh et al., C. R. Acad. Sci. Paris, Ser. I 343 (2006).Le problème de la génération des tsunamis est un sujet relativement récent. L'un des pionniers dans ce domaine fut Hammack [3]. Le but de cette Note est d'apporter une contribution à ce problème. La condition initiale utilisée dans les codes de propagation des tsunamis est souvent obtenue en translatant à la surface libre la déformation du fond suite à un tremblement de terre. Cette approche présente plusieurs inconvénients. Tout d'abord la dynamique du processus de génération est négligée. Il est évident qu'un glissement lent ne produit pas des vagues de même amplitude qu'un 500 D. Dutykh et al. / C. R. Acad. Sci. Paris, Ser. I 343 (2006) [499][500][501][502][503][504] glissement rapide. Ensuite le champ des vitesses initiales est également négligé. Nous présentons dans cette note un simple modèle de génération de tsunamis (voir [1] pour plus de détails).Le problème des ondes de surface est tout d'abord linéarisé (1)-(3) pour un fond qui a un mouvement prescrit (génération active). Il est résolu par la méthode des transformées de Laplace en temps et de Fourier en espace. En supposant que le mouvement du fond est instantané, on obtient pour la déformation de la surface libre η i (x, y, t) l'expression (10). Les vitesses peuvent également être calculées. Le problème des ondes de surface est ensuite linéarisé dans le cas où la déformation du fond est simplement translatée jusqu'à la surface libre (génération passive). Ce problème est différent du précédent. En effet, puisque le fond reste immobile en tout temps, la condition cinématique au fond devient (11). Par ailleurs, la condition initiale sur la surface libre devient η(x...

International audienceOyster farming structures are artificial obstacles which disturb tidal flow and wave propagation. These effects can induce modifications of erosion and sedimentation patterns, turbidity changes, local silting up and can be threatening for the shellfish farming itself. The understanding of the impact of these structures in terms of hydrodynamics and sediment dynamics in the far-field, i.e. at the scale of a bay, is a very challenging task. In order to investigate the far-field impact, it is very important to understand in the first place all the changes which occur at a smaller scale, i.e. at the scale of a single table for a farm consisting of oyster tables made of metallic wire structures on which porous bags of oysters are laid. This work is carried out through the idealized representation of the in-situ flow in a free surface flume tank. The flow characteristics around the overall structure are determined from velocity measurements obtained by laser velocimetry. The results highlight an asymmetric development of the boundary layers which suggest the existence of preferential areas for silting up and suspended matter fragmentation under the table

International audienceShellfish farming, particularly oyster farms, suffers from strong siltation phenomena which are harmful to the production of shellfish. The lack of knowledge about the impact of an oyster farm on the wave propagation and on the flow remains a significant difficulty for the comprehension of sediment transport processes in coastal zones. These effects are one of the possible sources of sedimentation. The study presented here focuses on describing finely hydrodynamical phenomena (velocity fields, turbulence parameters) around oyster tables. The analysis is based on experimental trials carried out in a flume tank on reduced models of oyster tables. Experiments highlight the flow perturbations in the near field and constitute a database for validation of numerical models developed at the same time. The model based on Navier–Stokes equations offers the possibility to study the impact of more realistic table lengths on the flow and to simulate the perturbation produced by a group of oyster tables. Both experimental and numerical results are presented in this paper