17 research outputs found
Characterisation of the Water Renewal in a Macro-Tidal Marina Using Several Transport Timescales
International audienceIn this paper, we investigate the water renewal of a highly populated marina, located in the southwest of France, and subjected to a macro-tidal regime. With the use of a 3D-numerical model (TELEMAC-3D), three water transport timescales were studied and compared to provide a fully detailed description of the physical processes occurring in the marina. Integrated Flushing times (IFT) were computed through a Eulerian way while a Lagrangian method allowed to estimate Residence Times (RT) and Exposure Times (ET). From these timescales, the return-flow (the fraction of water that re-enters the marina at flood after leaving the domain at ebb) was quantified via the Return-flow Factor (RFF) and the Return Coefficient (RC) parameters. The intrinsic information contained in these parameters is thoroughly analysed, and their relevance is discussed. A wide range of weather-marine conditions was tested to provide the most exhaustive information about the processes occurring in the marina. The results highlight the significant influence of the tide and the wind as well as the smaller influence of the Floating Structures (FS) on the renewal. Besides, this study provides the first investigation of the water exchange processes of La Rochelle marina. It offers some content that interest researchers and environmental managers in the monitoring of pollutants as well as biological/ecological applications
Erosions, dépots et transits sédimentaires associés dans le bassin de Marennes-Oléron
La gestion des sĂ©diments dans le bassin de Marennes-OlĂ©ron nĂ©cessite une connaissance des flux particulaires et des bilans sĂ©dimentaires Ă lâĂ©chelle du bassin, et une description des conditions dominantes dans lesquelles les transits se produisent. Un modĂšle de dynamique sĂ©dimentaire prenant en compte le transport simultanĂ© des sables et des vases sous lâeffet des vagues et des courants a Ă©tĂ© appliquĂ© au secteur cĂŽtier des Pertuis Charentais. La consolidation des vases et des mĂ©langes de sable et de vase est simulĂ©e. La validation est rĂ©alisĂ©e Ă lâaide de mesures de courant, de suivis altimĂ©triques en 8 points pendant un an, dâenregistrements de pression pour les vagues sur estran et de mesures de turbiditĂ©.
Une dissymĂ©trie entre lâest et lâouest du bassin pour la turbiditĂ© est constatĂ©e, en accord avec une circulation rĂ©siduelle nord/sud. Cette circulation moyenne gĂ©nĂ©rĂ©e par la marĂ©e entraĂźne un transit rĂ©siduel de matĂ©riel fin vers le sud, qui est partiellement piĂ©gĂ© dans le bassin. Le modĂšle identifie la zone Ă lâest du pertuis dâAntioche comme principale source de cette dĂ©rive, ce qui reste Ă valider. Les tempĂȘtes sont susceptibles dâinverser ces flux, mais sur des pĂ©riodes courtes. Pourtant, ce sont elles et les agitations locales qui gĂ©nĂšrent les fortes turbiditĂ©s. Le modĂšle met en Ă©vidence la variabilitĂ© de la nature du sĂ©diment superficiel, Ă lâĂ©chelle de la marĂ©e ou Ă la suite de tempĂȘtes
Dynamics and management of siltation in a macro-tidal marina: The case of La rochelle marina, France
International audienc
Temporal (1948-2012) and dynamic evolution of the Wouri estuary coastline within the gulf of Guinea
International audienceThe Wouri estuary is located in the Gulf of Guinea on the Atlantic coast of Cameroonâs coastline plain (3°49âČ and 4°04âČ north latitude and 9°20âČ to 9°40âČ east longitude), and is strongly influenced by coastal dynamics that have remained unquantified over a long period of time. This study analyzed the historical evolution of the Wouri estuarine coastline between 1948 and 2012. Variations in the estuarine evolution of the Wouri were studied from (i) minute topographic extracts from 1948, (ii) 1996â1999 nautical charts, and (iii) 2012 spatial map vectors. The net temporal spatial variation rates were calculated using the statistical methods of the Digital Shoreline Analysis System (DSAS). These change rates were also calculated over two time intervals (1948â1996 and 1996â2012) and over a 64-year period (1948â2012). The study reveals highly disparate results. Indeed, kinematics show that the Wouri estuary was dominated by erosion in its downstream section, with 262.83 ha for â3.2 m/year and 110.56 ha for â5.8 m/year between 1948â1996 and 1996â2012 respectively, and by accretion on the other hand in its upstream section, with 239.17 ha for 4.3 m/year in zone 5 between 1948â1996 and 150.82 ha for 12.6 m/year in zone 4 between 1996â2012. Thus, over the 64-year period (1948â2012), we have a dominance of variation by erosion downstream and conversely by accretion upstream, marked by the presence of amplifying factors (anthropogenic pressure and climate change) of the rate of variation of morphological evolution at the beginning of the 21st century, as compared to the middle-20th century. The observed development of sediment loss and accumulation, both influences and will influence, the sediment regime along the Wouri estuarine coastline. There is a need to develop a systematic sub-regional coastal surveillance activity to effectively manage Cameroonâs coastline syste
Ărosions, dĂ©pĂŽts et transits sĂ©dimentaires associĂ©s dans le bassin de Marennes - OlĂ©ron
Erosion and deposition patterns and associated sediment transport in the Marennes-Oléron bay (France)
Managing sediments in the baie de Marennes-OlĂ©ron (Atlantic coast of France) can be achieved providing particulate fluxes at the scale of the basin are available, as well as tidal and meteorological conditions during which major transports occur. A sediment dynamics model accounting for tide-and wave-induced sand and mud transport has been applied to the Pertuis Charentais area. Consolidation of pure mud and mixtures of sand and mud is accounted for. The model validation is achieved by current and turbidity measurements, local altimetric surveys during one year and pressure measurements for waves on the tidal flat. An asymmetry between eastern and western halves of the bay is observed on turbidity signals, in agreement with a residual circulation from north to south. This flow generates a net fine sediment transport towards the south. A part of it is deposited within the bay. According to the model, the eroded area east of Antioche inlet would be the main source of this southward flux : this feature has to be validated. The flux can be inversed during storms, but for a short duration. However, waves are dominant in the resuspension process. Last, the variability of sediment nature is demonstrated with the model, at different time scales in relation with tidal phases and storm.La gestion des sĂ©diments dans le bassin de Marennes-OlĂ©ron nĂ©cessite une connaissance des flux particulaires et des bilans sĂ©dimentaires Ă lâĂ©chelle du bassin, et une description des conditions dominantes dans lesquelles les transits se produisent. Un modĂšle de dynamique sĂ©dimentaire prenant en compte le transport simultanĂ© des sables et des vases sous lâeffet des vagues et des courants a Ă©tĂ© appliquĂ© au secteur cĂŽtier des Pertuis Charentais. La consolidation des vases et des mĂ©langes de sable et de vase est simulĂ©e. La validation est rĂ©alisĂ©e Ă lâaide de mesures de courant, de suivis altimĂ©triques en 8 points pendant un an, dâenregistrements de pression pour les vagues sur estran et de mesures de turbiditĂ©. Une dissymĂ©trie entre lâest et lâouest du bassin pour la turbiditĂ© est constatĂ©e, en accord avec une circulation rĂ©siduelle nord/ sud. Cette circulation moyenne gĂ©nĂ©rĂ©e par la marĂ©e entraĂźne un transit rĂ©siduel de matĂ©riel fin vers le sud, qui est partiellement piĂ©gĂ© dans le bassin. Le modĂšle identifie la zone Ă lâest du pertuis dâAntioche comme principale source de cette dĂ©rive, ce qui reste Ă valider. Les tempĂȘtes sont susceptibles dâinverser ces flux, mais sur des pĂ©riodes courtes. Pourtant, ce sont elles et les agitations locales qui gĂ©nĂšrent les fortes turbiditĂ©s. Le modĂšle met en Ă©vidence la variabilitĂ© de la nature du sĂ©diment superficiel, Ă lâĂ©chelle de la marĂ©e ou Ă la suite de tempĂȘtes.Le Hir Pierre, Kervella StĂ©phane, Walker Patrice, Brenon Isabelle. Ărosions, dĂ©pĂŽts et transits sĂ©dimentaires associĂ©s dans le bassin de Marennes - OlĂ©ron. In: 31Ăšmes JournĂ©es de lâHydraulique de la SociĂ©tĂ© Hydrotechnique de France. Morphodynamique et gestion des sĂ©diments dans les estuaires, les baies et les deltas. 22 et 23 SEPTEMBRE 2009. 2009
Fortnightly tidal asymmetry inversions and perspectives on sediment dynamics in a macrotidal estuary (Charente, France)
Tidal asymmetry is a phenomenon that characterises estuarine hydrodynamics and has a strong impact on sediment dynamics. Extensive research has been dedicated to studying tidal dynamics in semidiurnal macrotidal estuaries, highlighting several general principles. The ratio of flood to ebb peak velocities and differences in ebb and flood durations are often used to characterise the asymmetry encountered in estuaries. In the Charente estuary (French Atlantic coast), water surface elevation data obtained using an ADCP (Acoustic Doppler Current Profiler) and a tide gauge show that the duration asymmetry undergoes inversions during the spring-neap tidal cycle. A two-dimensional hydrodynamics model is used to investigate the connection between spring-neap inversions of the tidal asymmetry and the harmonic composition of the tide. Different constituents (M2, S2, M4 and MS4) are considered at the open boundary. The results show that M4 and MS4 play a key role in the occurrence of these inversions. The influence of the morphology is also discussed and modifications of the bathymetry are performed to evaluate its impact. In the Charente estuary, the existence of both externally and internally generated overtides thus results in a spatially and fortnightly variable tidal asymmetry. The modelled barotropic tidal currents are used to estimate the possible impact on sediment dynamics. The results suggest that asymmetry inversions tend to create sediment accumulation in an intermediate zone between the river mouth and Rochefort, located approximately 20 km upstream
PAMELi, un drone marin de surface au service de lâinterdisciplinaritĂ©
International audienc