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.

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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.

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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.

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The southern coast of Argentina is known for its high tidal ranges and large coarse-grained coastal barriers that have emerged over time as a result of the regional uplift. Well-preserved barriers can provide critical information about the morphological evolution of the coastal areas, and the relative evolution of the mean sea level, as long as their morphodynamics are well understood. In order to better understand the influence of tides in wave-built sedimentary bodies, an in-depth analysis of the architecture of a barrier system has been realized at the mouth of the Santa Cruz - Chico river estuary (50°S). Maximum tidal range in this estuary is 12 m. A great variety of morphologies compose both sides of the estuary inlet, from simple ridges and barrier spits to beach ridge plains. Barrier spits and beach ridge plains characterize the southern side, whereas elongated simple ridges and barrier spits isolating large tidal flats are more developed on the northern side. The site was investigated using ground-penetrating radar combined with digital elevation model analysis, and some sedimentological observations. Cross-shore profiles, with a penetration depth up to 5 m, show a large range of radar facies attributed to erosional surfaces, beach face progradation, and washover deposits. The slope of the beach face appears to be an effective parameter for differentiating between beach ridges plains and barrier spits, as the latter are characterized by steeper values. The combined analysis of the radar architecture and barrier morphology allows to identify five barrier sets, which have been associated with five different development stages along the late Quaternary: 1) Last Interglacial Maximum (MIS 5e), 2) Last Interglacial (MIS 5e/5c/5a), 3) Mid Holocene transgressive maximum, 4) Mid Holocene highstand reworking, and 5) Holocene regressive stage. Although the morphological model is in line with the observations made by other authors, it would be appropriate to consolidate the model by establishing an absolute chronology.

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Coastal zones face increasing vulnerability due to climate change, leading to hazards like coastal flooding or beach erosion, exacerbated by anthropogenic activities and global warming. Effective coastal management and adaptation strategies are crucial. Advanced numerical models and monitoring of extreme storms are essential for accurate risk assessment and early warning systems. The DYNSEEC project aims to enhance understanding of storm dynamics, focusing on coastal flooding to improve risk assessment and mitigation efforts. This dissertation examines extreme waves and storm surges along the English Channel, integrating global climate oscillations and local hydrodynamic factors. Normandy’s beaches, with diverse morphologies, are studied using numerical modelling and monitoring systems to understand hydrodynamics and coastal risks.The stochastic drivers of maritime hydrodynamics are explored, focusing on wave height and sea level variations, analyzed through statistical and spectral methods. The research identifies significant variability in surges driven by long-term sea level trends and tide-surge interactions, with wave heights influenced by ocean-atmosphere interactions, and revealing dependencies on sea surface temperature, sea level pressure, and climate indexes. A classification of typical extreme events on the English Channel is lastly performed.A simulation of 40 years of data, with validation against buoy and tide gauge measurements in England and France has been carried out. The study classifies storms, assessing their impact on Normandy’s coast, showing significant wave height variations, dependent mostly on their origin and direction of propagation, primarily the Atlantic Ocean. Detailed simulations emphasize coastal morphology’s role in energy dissipation and wave behavior.The numerical modeling to simulate storm wave dynamics at three Norman coastal sites is detailed, validated by comparing simulations with buoy measurements, theoretical formulations, and wave run-up data measured by Video Monitoring Systems. Results show that run-up height is influenced by water levels and wave height, with site-specific variations due to beach characteristics, mainly the porosity of gravels and pebbles.The stochastic and the numerical methodologies and databases from previous studies are finally applied to link hydrodynamics with beach morphodynamics under extreme conditions, studying compound flooding on the Seine Bay and the impact of coastal structures and beach permeability on beach erosion.

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The Surface Water and Ocean Topography (SWOT) altimeter will perform a continuous global water survey with unprecedented resolution and accuracy across its 3-year mission. After being launched on December 16th 2022 with a SpaceX Falcon 9 rocket from Vandenberg in California, it was successfully commissioned followed by a Calibration and Validation (Cal/Val) phase that lasted approximately between April and July 2023. During this period, numerous in-situ measurements were performed across the globe to assess the altimeter's performance. Airborne Light Detection And Ranging (LiDAR) campaigns were conducted off the coasts of Normandy, France as part of other measurements in this region. We carried out 4 different missions, 2 in May and 2 in June, using a Leica ALS 60 airborne sensor aboard 2 different planes, a Piper Navajo and a Swearingen Fairchild Merlin. The flight plans were designed below the SWOT Ka-band Radar Interferometer (KaRIn) along and across the 1-day fast sampling ground track. Ground Control Points (GCP) were acquired under the LiDAR coverage, close to the city of Cherbourg. The plane's trajectory was processed using CNES GINS software, using the integer Precise Point Positioning (iPPP) mode, resulting in centimetric antenna phase positioning. LiDAR data were calibrated using the GCPs with a millimetric average accuracy. First results between SWOT data and airborne LiDAR indicate very good consistency. Indeed, the differences between the SWOT LR 2 km pre-cal product and LiDAR data, averaged over a similar 2 km grid, gives centimetric standard deviation.

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