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UMR 6143 "Morphodynamique Continentale et Côtière"
Le laboratoire Morphodynamique Continentale et Côtière (M2C) est une Unité Mixte de Recherche (UMR 6143) créée en 1996. Il est rattaché au CNRS (INSU en principal et INEE en secondaire), à l’Université de Caen Normandie (UNICAEN) et à l’Université de Rouen Normandie (URN).
Les recherches du laboratoire M2C s’intéressent à la caractérisation et à la modélisation de la dynamique des processus naturels et des différents compartiments, le long du continuum TERRE-MER, à différentes échelles de temps et d’espace. Les recherches s’organisent en 3 thèmes :
Les recherches du laboratoire M2C s’intéressent à la caractérisation et à la modélisation de la dynamique des processus naturels et des différents compartiments, le long du continuum TERRE-MER, à différentes échelles de temps et d’espace. Les recherches s’organisent en 3 thèmes :
- Bassins versants
- Estuaire
- Côtier
Ces recherches sont réalisées avec une approche interdisciplinaire intégrant des chercheurs spécialisés en mécanique, géosciences, océanographie et hydrologie, microbiologie et biologie des organismes.
En raison de la réponse qu’elles constituent aux attentes des gestionnaires, collectivités et industriels, les activités que nous menons en matière de valorisation s’inscrivent dans le cadre de différentes recherches appliquées.
Nos recherches couplent la mesure in situ grâce à de nombreux équipements dédiés (voir rubrique plateaux techniques), des approches expérimentales et de modélisations numériques.
Dépôts
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Evolution des dépôts
Dernières publications
Coastal boulder deposits, observed worldwide, provide geomorphological evidence of extreme wave events such as storms, hurricanes and tsunamis. Theoretical formulations have been developed for determining hydrodynamic conditions responsible for boulder emplacement on the shore, which increasingly make use of boulder geometry and associated site geomorphology. Nevertheless, information on extreme events responsible for the emplacement of coastal boulders is rarely available, meaning there has been limited opportunity to test existing formulations in the light of real hydrodynamic and geomorphic data. In this study, we take advantage of the important record of coastal boulder deposits on Cuba Island to compare the hydrodynamic parameters (minimum flow velocity) deduced from the boulders' morphology and emplacement characteristics, with hydrodynamic conditions (maximum wave height and orbital velocity) that occurred during the tropical cyclones responsible for the boulders' actual emplacement. We selected four sites where three hurricanes have emplaced five boulders on low-lying coral reef terraces over the last 50 years. Using terrestrial Structure-from-Motion photogrammetry, we determined with precision the boulders' shape and volume, which in combination with density, mode of emplacement and distance from the shore, were used to calculate the minimum flow velocity responsible for dislocation of the coral reef terrace and inland transport. To serve as comparisons, available modelled data of wave height and period were used to estimate the maximum orbital velocity that possibly occurred during the weather event using linear wave theory. Our results show that for all boulders studied except one, there is a good agreement between the values of minimum flow and maximal orbital velocities, with minimum flow velocities for boulder emplacement consistently smaller than the maximum wave orbital velocity during the weather event. The difference observed for one boulder is attributed to specific site effects, highlighting in this case the limitation of using distant hydrometeorological data for characterizing wave processes responsible for coastal boulder deposits. Helped by detailed data collected on boulders with large differences in morphology including size, and mode of emplacement, this study confirms the pertinence of using formulations relating boulder morphology and site characteristics to the minimum flow velocity that detached and transported the boulder. It further emphasizes the importance of obtaining adequate boulder and geomorphic setting characterizations to link geomorphological proxies and extreme wave events. © 2024 The Authors
The architecture and chronology of Late Pleistocene to Holocene alluvial deposits in the lower Garonne have been studied in details based on data (boreholes, trenches, ground-penetrating radar profiles, numerical dating) collected in quarries and during archaeological surveys. The preserved alluvial bodies, dated between ca. 38 ka and present, show that the river retained a meandering or anabranching pattern throughout this period, associated with the formation of lateral accretion packages and scroll bars in the convexity of meanders. Valley incision in connection to the LGM low sea level reached up to 19 m in the study area, and occurred between ca. 26 and 18 ka. Since ca. 18 ka, the lateral migration of meanders widened the plain without any significant incision of the Oligocene marl bedrock. The Early-Middle Holocene was characterized by the development of highly sinuous meanders, while sinuosity decreased in a late phase including the Little Ice Age. Comparison with other lowland European rivers shows that the persistence of a meandering or anabranching pattern during MIS 2 is not an isolated case. The documented examples are associated with rivers typified by low valley slope, or situated in southern regions unaffected by permafrost and characterized by dense vegetation. The latter conditions would not have led to a drastic change in river discharge and bedload transport during the Last Glacial, as was the case for more northerly rivers where braiding seems to have been common.
Simulating sediment dynamics in a large and energetic estuary system remains challenging, primarily due to the spatial and temporal complexities of the interaction between flow and sediment transport, especially for sand-mud mixtures. This study uses a three-dimensional (3D) numerical model, based on the open TELEMAC system, to investigate the dynamics of suspended sediment concentration (SSC) in the Gironde Estuary, a complex estuarine environment characterized by an estuarine turbidity maximum (ETM) and significant variations in river discharge. The main contributions of this study include addressing the challenges of coupling bed friction with sediment transport of the sand-mud mixture for feedback on bed roughness and bottom depth changes and the ability of the model to capture the migration of ETM from high to low flow. Additionally, the current study analyzes the ability of the model to capture the migration of ETM from high to low flow, and it utilizes a calibration strategy that minimizes parameters by using in situ data and encompassing hydroemorpho-sedimentary interactions. A sensitivity analysis was done using different settling velocity approaches and sediment classes to establish an optimal model configuration and the uncertainty associated with the reduced model parameterization is discussed. The model satisfactorily reproduces the hydrodynamic features, particularly when the hydro-sedimentary feedbacks are taken into account, the seasonal trend of SSC, springneap variations, and the development of a well-defined ETM. The selection of a specific formulation for the settling velocity influences the location and magnitude of ETM. The van Leussen formula not only predicts a broad movement of ETM from high to low river flow, but also predicts high turbidity for extended periods during low river flow. Conversely, two empirical formulas from Le Hir and Defontaine predicted the highest turbidity during neap tides but sediment losses during prolonged simulations. The results of this study contribute to a deeper understanding of sediment dynamics in the Gironde Estuary, providing valuable information for future estuarine modeling and management.
Sedimentary infilling of estuaries and embayment is the result of complex interactions between tide asymmetry and circulation patterns, wave climate and autocyclic channel dynamics. Their morphological evolution is dependent on a sensitive balance between sediment fluxes and available space, which can be altered by climate change and subsequent rising sea level. Predicting the future evolution of such environments is crucial to anticipate the modification of ecosystems at the land-sea interface, and to evaluate the potential impacts on human activities (navigation, exploitation of marine resources, tourism and recreation, etc.). In this context, sediment transport in a hypertidal sandy bay (bay of Somme, NW France) is studied using numerical modeling in combination with in-situ data at the bay scale and for a 2-week period in order to understand the processes involved in filling the bay. A 3D fully coupled hydrodynamics-wave-sediment model, combining a hydrodynamic model (CROCO) to a spectral wave model (WAVEWATCH-III), both feeding a sediment transport model developed by USGS, is implemented. After a validation step involving the realistic simulations of nearshore hydrodynamics under tide, wave and wind forcings, based on in-situ data from two field campaigns, the coupled model is considered reliable for sediment transport assessment. Then, bay-scale simulations are carried out for a broad range of metocean conditions, from calm to storm seas and for spring and neap tide events. Our main conclusions are as follows: i) with a maximum tidal range of 10 m, semi-diurnal tide is unsurprisingly the main driver of the bay hydrodynamics, ii) the bay fills with seawater during the flood and empties during the ebb, iii) the wave-induced circulation appears to have a significant impact on the bay sand filling during the storm and iv) ocean waves generate a longshore current at the bay entrance, which is intense and unstable during the storm, showing significant cross-shore velocities that influence sediment transport. Next step is to evaluate the consequences in terms of morphodynamics.
This paper presents the results of the 2022 Groundwater Time Series Modelling Challenge, where 15 teams from different institutes applied various data-driven models to simulate hydraulic-head time series at four monitoring wells. Three of the wells were located in Europe and one was located in the USA in different hydrogeological settings in temperate, continental, or subarctic climates. Participants were provided with approximately 15 years of measured heads at (almost) regular time intervals and daily measurements of weather data starting some 10 years prior to the first head measurements and extending around 5 years after the last head measurement. The participants were asked to simulate the measured heads (the calibration period), to provide a prediction for around 5 years after the last measurement (the validation period for which weather data were provided but not head measurements), and to include an uncertainty estimate. Three different groups of models were identified among the submissions: lumped-parameter models (three teams), machine learning models (four teams), and deep learning models (eight teams). Lumped-parameter models apply relatively simple response functions with few parameters, while the artificial intelligence models used models of varying complexity, generally with more parameters and more input, including input engineered from the provided data (e.g. multi-day averages). The models were evaluated on their performance in simulating the heads in the calibration period and in predicting the heads in the validation period. Different metrics were used to assess performance, including metrics for average relative fit, average absolute fit, fit of extreme (high or low) heads, and the coverage of the uncertainty interval. For all wells, reasonable performance was obtained by at least one team from each of the three groups. However, the performance was not consistent across submissions within each group, which implies that the application of each method to individual sites requires significant effort and experience. In particular, estimates of the uncertainty interval varied widely between teams, although some teams submitted confidence intervals rather than prediction intervals. There was not one team, let alone one method, that performed best for all wells and all performance metrics. Four of the main takeaways from the model comparison are as follows: (1) lumped-parameter models generally performed as well as artificial intelligence models, which means they capture the fundamental behaviour of the system with only a few parameters. (2) Artificial intelligence models were able to simulate extremes beyond the observed conditions, which is contrary to some persistent beliefs about these methods. (3) No overfitting was observed in any of the models, including in the models with many parameters, as performance in the validation period was generally only a bit lower than in the calibration period, which is evidence of appropriate application of the different models. (4) The presented simulations are the combined results of the applied method and the choices made by the modeller(s), which was especially visible in the performance range of the deep learning methods; underperformance does not necessarily reflect deficiencies of any of the models. In conclusion, the challenge was a successful initiative to compare different models and learn from each other. Future challenges are needed to investigate, for example, the performance of models in more variable climatic settings to simulate head series with significant gaps or to estimate the effect of drought periods.
Environmental imprint of inorganic fertilizer uses was assessed over the last hundred years at the downstream part of large French rivers (Loire, Moselle, Rhine, Rhone, Meuse and Seine rivers) based on Potassium-40 (40K) activity concentration data sets acquired from soil monitoring (1980–2022) and from sediment coes collected from 2020 to 2022 to reconstruct the temporal trajectories of 40K activity concentrations since the beginning of the last century. Cultivated soils were significantly enriched in 40K compared to non-cultivated ones in the 1980s and 1990s when they turned back to the contents of non-cultivated soils during the following decades. In riverine sediments, all the rivers displayed close 40K temporal trajectories with peaking 40K contents in fine grain size sediments in the 1980s. Maximum 40K enrichment factors from this period were related to the proportion of agricultural areas in the river catchment. In the Loire and Moselle rivers, some high 40K contents were associated with sandy sedimentary strata deposited by flood events before the end of the 1950s due to the presence of potassium enriched minerals. The comparison of 40K activity concentration in sediments with potassic fertilizer delivery in France highlighted very similar temporal trajectories giving evidence that the uses of potassic fertilizers imprint the riverine sediments of most French large rivers. Finally, the environmental resilience face to this anthropic pressure was fast as 40K levels decreased immediately after the decreases of the delivery in most of cases.
Carbon-14 (14C) has a natural origin but is also anthropogenically released from civil nuclear facilities. Due to its long decay period (half-life: 5700 ± 30 years), it is a persistent radionuclide in the environment. In rivers, the complex speciation of carbon makes the fate of industrial 14C difficult to track. This study reports a first overview of artificial 14C cycling in a nuclearized river. A one-year sampling campaign was conducted on the French nuclearized Rhône River and two of its non-nuclearized tributaries (Durance and Ardèche rivers). Isotopic (δ13C, Δ14C) and carbon concentrations analyses were performed on the particulate organic carbon (POC), dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC). Chlorophyll-a (Chl-a) and tritium analyses were performed to assess the dynamic of aquatic organic matter and the nuclear industry contribution, respectively. Comparisons of Δ14C data obtained from the Rhône River with those from the tributaries highlight significant industrial radiocarbon labelling in all carbon forms, with medians of 142, 130 and 42 ‰ for POC, DOC and DIC, that are 2–3 times higher than those of the tributaries. The high values of Chl-a/POC ratios with Δ14C-enriched POC suggest a biological uptake of artificial Δ14C in DIC by aquatic photosynthesis. The relationship of Δ14C-DIC with tritium activity indicates a response to recent releases and enables the contribution of nuclear power plants to be estimated at a median of 26 %. Sampling at the Rhône's mouth would reinforce our understanding of the fate of riverine 14C when entering the marine environment.
Mots-Clés
Modelling
Normandie
Inverse problem
Autocorrelation
Neogene
Introduced species
Morocco
Niger
Modélisation
Seine
NAO
Sediment
Alderney Race
Inversion
Eastern English Channel
Paris Basin
GIS
Sediment transport
ACL
Bay of Seine
Géomorphologie
Offshore wind farms
Normandy
Erosion
Non-indigenous species
Géochimie
Mediterranean Sea
Marine Renewable Energy
Sediment core
Hydraulic tomography
Wastewater
Turbulence
Deep learning
SEDIMENT
Hyperspectral imaging
English channel
Hydrodynamics
Washover
Non-native species
Biodiversity
Pleistocene
Benthic macrofauna
Algeria
Manche
Groundwater
Ground-penetrating radar
Tomography
Holocene
Antibiotic resistance
Geochemistry
France
Organic matter
Marine terrace
Modeling
Marine renewable energy
Ecological Network Analysis
Sediments
English Channel
Numerical modeling
Tectonics
Bassin versant
Hydrogeophysics
Sahel
Coastal barrier
Bacteria
Morphodynamique
Stratigraphy
Morphodynamics
Sedimentology
Quaternary
Climate change
Hydrology
Littoral
Baie de Seine
Géoradar
Watershed
Climate
Rock-Eval pyrolysis
Anthropogenic impact
Estuary
Seine estuary
Topography
Karst
Offshore wind farm
Aquaculture
Physical modelling
Sédimentologie
Geomorphology
Granulométrie
Benthos
Ecosystem functioning
Sampling strategy
Numerical modelling
Mediterranean
Diversity
Sédiments
Biomass
Stratigraphie
Hypertidal
Chemometrics
Collaborations internationales
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