Interactions entre le comportement mécanique des ouvrages de défense pour la protection du littoral et les processus hydro-sédimentaires contrôlant la dynamique du trait de côte : approche expérimentale couplée numérique
Dans un contexte d’augmentation des risques de submersion et d’érosion des littoraux, les gestionnaires disposent de plusieurs méthodes pour mieux prévenir les risques associés. L’une d’elles consiste à travailler avec les défenses dites « dures » existantes en les étendant ou en les renforçant. L’objectif général de ce travail est de mieux comprendre les interactions entre l’hydrodynamique et ce type d’ouvrages de défense déployés en haut de plage et, plus particulièrement, les enrochements. Pour cela, différents processus hydrodynamiques en jeu sur le haut de plage, tels que les ondes longues ou infragravitaires et l’aquifère côtier, sont étudiés en parallèle avec le comportement des enrochements. Dans un premier temps, différentes méthodes de décomposition du signal de la surface libre, en composantes dirigées vers le large et vers la côte, ont été explorées afin d’analyser ensuite les transformations des ondes infragravitaires en condition de tempête sur une plage sableuse protégée par un enrochement. Dans un second temps, des données expérimentales ont été utilisées pour calibrer des simulations numériques réalisées avec le modèle XBeach en 2D (mode SurfBeat). L’analyse de ces simulations a mis en évidence l’importance de la bathymétrie et du modèle de déferlement choisi pour configurer le modèle numérique. Une génération significative d’ondes infragravitaires ainsi que la formation d’ondes stationnaires ont été observées. En condition de houle modérée, les données montrent une corrélation entre le R2% (proxy couramment utilisé pour prédire le runup) et les variations bathymétriques parallèles à la côte au niveau de la barre externe. Aucun impact notable de l’enrochement sur la réflexion des ondes infragravitaires n’a été observé dans ces conditions. Des données expérimentales collectées sur la plage de Lacanau ont également été analysées pour étudier la dynamique de l’aquifère côtier sous une plage sableuse avec enrochement, soumise aux marées et aux vagues. Une cellule de recirculation a été identifiée, sans toutefois détecter d’effet immédiat notable de l’enrochement. Enfin, un modèle numérique, basé sur la méthode des éléments discrets a été développé avec le logiciel LMGC90. Cette première approche fournit une base et des éléments de recherche sur la réponse géomécanique des ouvrages tels que les enrochements, sous l’effet des phénomènes de runup et de vagues.
(10/12/2024)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Influence of Rocky Obstacle Sand Bypassing on Embayed Beach Dynamics Using a Reduced-Complexity Shoreline Model
Headland and groyne sand bypassing greatly influences embayment dynamics at medium to long timescales, but is often disregarded or partially included in reduced-complexity shoreline models. This study explores how accounting for subaqueous sediment bypassing in a shoreline model affects mean embayed beach planshape and spatial variability. We implement a generic parametrization of sand bypassing in the LX-Shore model, with simulations on a synthetic embayment in two configurations: "full bypassing" (FB) where the sediments bypass the obstacle in the surfzone and beyond, and "shoreline bypassing" (SB) where bypassing occurs only when the shoreline extends beyond the obstacle. Time-invariant wave simulations show significant differences in updrift shoreline position between FB and SB. Simulations with time-varying wave angles and fixed wave height and period reveal that FB significantly impacts the embayment mean planform and spatial variability: FB reduces beach rotation by about 1/3, particularly under slightly oblique and slightly asymmetrical wave climates, and decreases shoreline curvature, especially under highly oblique wave climates. Downdrift shoreline erosion may be overestimated by up to 20% under SB. Our simulations provide new insight into the influence of subaqueous sand bypassing on embayed beach dynamics and emphasize the importance of including this process when modelling shoreline evolution in coastal embayments.
(Journal of Marine Science and Engineering. vol. 12, n° 2077-1312, pp. 2266, 10/12/2024)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, BRGM, BW-CGC
Fate of per- and polyfluoroalkyl substances (PFAS) in estuaries : focus on interactions with suspended sediments.
To understand the fate of legacy and emerging PFAS at the land-sea interface, this work focused on the interactions with estuarine sediments. More precisely, we mainly studied the influence of co-existing PFAS, salinity (S) and suspended particulate matter (SPM) on the sediment-water partitioning of PFAS. First, to investigate the effect of coexisting PFAS on their adsorption and desorption, competitive adsorption and desorption experiments were conducted using single and mixed PFAS solutions at low concentrations, using kaolinite as model sorbent. Selected PFAS include eight perfluoroalkyl carboxylates (PFCAs), two perfluoroalkyl sulfonic acids (PFSAs) and one zwitterionic PFAS (8:2 fluorotelomer sulfonamide alkylbetaine (8:2 FTAB)), which were studied in three single-solute solutions and two mixture solutions. A pseudo-second-order kinetic model was used to fit in the adsorption and desorption kinetics data correctly. Their sorption and desorption on kaolinite were quite fast, with equilibrium reached within 2h. Sorption processes appeared to be influenced by the PFAS molecular structure: sorption increased and desorption decreased with increasing fluoroalkyl chain length, characterized by the increase of log Kd. Besides, PFSAs (i.e, PFHxS and PFOS) had greater sorption and weaker desorption than PFCAs (i.e, PFHpA and PFNA) with similar fluoroalkyl chain. The zwitterionic 8:2 FTAB showed stronger sorption and smaller desorption than anions (i.e., PFOS or PFNA) with a similar fluoroalkyl chain. Sorption and desorption data obtained for single and multi-solute experiments indicated that there was no significant statistical difference between such conditions. Thus, the influence of competitive adsorption and desorption was negligible at low concentrations. To study the influence of salinity and SPM on the sorption of PFAS, we used a sediment sample collected in the fluvial sector of the Garonne-Gironde system. We performed sorption kinetics and sorption isotherms tests for the same PFAS, under 35 combination of salinity and turbidity. Based on response surface methodology (RSM) modelling approach, results indicated the sorption kinetics of PFAS onto sediment can be described by pseudo-second-order model and 24h is the equilibrium time for targeted PFAS. Besides, PFAS sorption can be well fitted by linear model and Freundlich model, the linear sorption range for PFAS studied was in the range of 0.12 to 1.31 nM (equilibrium concentration). Moreover, based on RSM modelling approach, we found that Kd varied between 0.62 and 55271 L/kg and that both S and SPM were significant factors, i.e. the Kd of PFAS was positively related to S due to salting-out effect while it was negatively related to SPM concentration. Moreover, SPM had a stronger effect than salinity (S) for PFHxA and PFHpA, whereas S was the more dominant factor for most other compounds. For PFUnDA and 8:2 FTAB, S and SPM displayed nearly equivalent weights as drivers of Kd. In addition, a negative interaction between both factors was observed, i.e. if SPM increases, the effect of S on Kd is weaker. Overall, this work provides original results to model the sorption of legacy and emerging PFAS on estuarine sediments based on RSM modelling approach. It provides a new perspective to investigate the fate of PFAS at the land-sea interface.
(10/12/2024)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Circulation in a tropical embayment with two inlets and complex geometry: The Itamaracá-Itapessoca system, Brazil
Along the northeast coast of Brazil, numerous estuaries with intricate morphologies, characterized by multiple channels, islands, and intertidal areas, are found. These estuaries undergo significant seasonal variations, experiencing pronounced wet and dry periods. While some of these systems have small drainage basins with minimal freshwater inflow and sediment production, they boast extensive intertidal mangrove areas. This study focuses on assessing the hydrodynamics and residual circulation of the Itamaracá-Itapessoca Estuarine System (IIES) to elucidate the impact of residual circulation on estuary-shelf exchange dynamics. The IIES comprises two main islands and two inlets surrounded by extensive intertidal areas. Field observations collected during the wet season were used to calibrate and validate a numerical model. Two model scenarios were examined: a 'dry' scenario, considering hydrodynamics driven solely by interactions between morphology and tides, and a 'wet' scenario, incorporating freshwater inflow. Key findings include: (a) the inclusion of freshwater inflow minimally alters system dynamics; (b) tidal dynamics are amplified within the system, resulting in a null zone between the inlets; and (c) residual circulation circulates around the islands, with net importation through the larger inlet and net exportation through the smaller one. The intensity of exchange is heightened under wet conditions.
(Regional Studies in Marine Science. vol. 77, n° 2352-4855, pp. 103671, 01/12/2024)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Dynamics of Cu and Pb during sediment remobilization and associated risk for coastal water quality
Laboratory resuspension experiments were performed using three sediments and seawater, contrasted in terms of metals concentration/contents, metals partitioning in sediments as well as physical-chemical characteristics of both sediment and seawater. The aim of the study was to examine if the variability in metals content and metals distribution onto carrier phases are influencing the dynamics of metal transfers from and to sediment. Since Cu and Pb are classical contaminants found in coastal areas, their dissolved concentrations were monitored (up to 360 h) to assess their release or removal by particles, with a particle concentration of 2.5 g L−1 (wet weight). The dynamics of Cu and Pb transfers were similar between experiments while the amplitude of transfers was specific to each sediment. The results of the study clearly demonstrated that while Cu first undergoes an adsorption onto particles (after few minutes of mixing), Pb first undergoes a desorption from particles (after few hours of mixing). Then Cu was desorbed from particles (from 48 to 360 h), while Pb remained adsorbed onto particles (from few 24 to 360 h). The impact of the quantity of resuspended particles was evaluated after 24 h (Pb) and 360 h (Cu) of mixing with different sediment:water ratio. The increase of resuspended particles leads to a non-linear release of dissolved Cu with Cu concentration overpassing the trigger values to protect 80 % (La Spezia), 90 % (Toulon) and 95 % (Olbia) marine species as defined by the ANZECC (Australian and New Zealand Environment and Conservation Council). On the contrary, the increase of resuspended particles leads to a bell-shaped curve for dissolved Pb pointing out Pb affinity for particles.
(Science of the Total Environment. vol. 957, n° 0048-9697, pp. 177476, 01/12/2024)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Anthropogenic legacy of potassium-40 in French large rivers reconstructed from sediment cores
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.
(Science of the Total Environment. vol. 954, n° 0048-9697, pp. 176479, 01/12/2024)
IRSN/PSE-ENV/STAAR/LRTA, IRSN/PSE-ENV/STAAR, IRSN, METIS, EPHE, PSL, INSU - CNRS, SU, CNRS, IRSN/PSE-ENV/SPDR/LT2S, IRSN/PSE-ENV/SPDR, IRSN, IRSN/PSE-ENV/SAME/LMRE, IRSN/PSE-ENV/SAME, IRSN, LIEC, INSU - CNRS, UL, CNRS, ITES, ENGEES, UNISTRA, INSU - CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, M2C, UNICAEN, NU, INSU - CNRS, UNIROUEN, NU, CNRS, GéHCO, UT
Decadal Prediction Centers Prepare for a Major Volcanic Eruption
The World Meteorological Organization’s Lead Centre for Annual-to-Decadal Climate Prediction issues operational forecasts annually as guidance for regional climate centers, climate outlook forums, and national meteorological and hydrological services. The occurrence of a large volcanic eruption such as that of Mount Pinatubo in 1991, however, would invalidate these forecasts and prompt producers to modify their predictions. To assist and prepare decadal prediction centers for this eventuality, the Volcanic Response activities under the World Climate Research Programme’s Atmospheric Processes and Their Role in Climate (APARC) and the Decadal Climate Prediction Project (DCPP) organized a community exercise to respond to a hypothetical large eruption occurring in April 2022. As part of this exercise, the Easy Volcanic Aerosol forcing generator was used to provide stratospheric sulfate aerosol optical properties customized to the configurations of individual decadal prediction models. Participating centers then reran forecasts for 2022–26 from their original initialization dates and, in most cases, also from just before the eruption at the beginning of April 2022, according to two candidate response protocols. This article describes various aspects of this APARC/DCPP Volcanic Response Readiness Exercise (VolRes-RE), including the hypothesized volcanic event, the modified forecasts under the two protocols from the eight contributing centers, the lessons learned during the coordination and execution of this exercise, and the recommendations to the decadal prediction community for the response to an actual eruption.The World Meteorological Organization’s Lead Centre for Annual-to-Decadal Climate Prediction issues operational forecasts annually as guidance for regional climate centers, climate outlook forums, and national meteorological and hydrological services. The occurrence of a large volcanic eruption such as that of Mount Pinatubo in 1991, however, would invalidate these forecasts and prompt producers to modify their predictions. To assist and prepare decadal prediction centers for this eventuality, the Volcanic Response activities under the World Climate Research Programme’s Atmospheric Processes and Their Role in Climate (APARC) and the Decadal Climate Prediction Project (DCPP) organized a community exercise to respond to a hypothetical large eruption occurring in April 2022. As part of this exercise, the Easy Volcanic Aerosol forcing generator was used to provide stratospheric sulfate aerosol optical properties customized to the configurations of individual decadal prediction models. Participating centers then reran forecasts for 2022–26 from their original initialization dates and, in most cases, also from just before the eruption at the beginning of April 2022, according to two candidate response protocols. This article describes various aspects of this APARC/DCPP Volcanic Response Readiness Exercise (VolRes-RE), including the hypothesized volcanic event, the modified forecasts under the two protocols from the eight contributing centers, the lessons learned during the coordination and execution of this exercise, and the recommendations to the decadal prediction community for the response to an actual eruption.
(Bulletin of the American Meteorological Society. vol. 105, n° 0003-0007, pp. E2496-E2524, 01/12/2024)
CCCma, ECCC, ISAS, U of S, MPI-M, NIA, LaRC, BCCR, BIO / UiB, UiB, NERSC, BSC-CNS, GFDL, NOAA, UCAR, LOCEAN-VARCLIM, LOCEAN, MNHN, IRD, INSU - CNRS, SU, CNRS, IPSL (FR_636), ENS-PSL, UVSQ, CEA, INSU - CNRS, X, CNES, SU, CNRS, UPCité, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LMD, INSU - CNRS, X, IP Paris, ENPC, SU, CNRS, ENS-PSL, PSL, LASG, IAP, CAS, LASW, CAMS, CAMS, MOHC, JAMSTEC, AORI, UTokyo
Environmental changes in the Fleuve Manche paleoriver drainage system (Western Europe) linked to North Atlantic sub-millennial climate variability across Heinrich Stadial 1: Palynological evidence from the Bay of Biscay
Marine microfossils (dinoflagellate cysts and planktonic foraminifera) and geochemical (XRF-Ti/Ca)-based climatic records from a core (MD13–3438) located off the Fleuve Manche (FM) paleo-mouth have revealed that sustained warm summer sea surface temperatures (SSTs) during sub-millennial climate changes within HS1 (~18–14.7 ka) may have played a key role in the FM regime related to the European Ice Sheet (EIS) melting rate. In this study, we have analyzed the MD13–3438 pollen content over the HS1 at a mean resolution of ~50 years to test whether vegetation-based air temperatures were coupled to SSTs face to this rapid climate variability. First, our results highlight two major phases of pollen sources at site MD13–3438, preventing the pollen record to be interpreted as a continuous record of the evolution of vegetation and climate occupying a single watershed across HS1. The first phase, i.e. the HS1-a interval (~18–16.8 ka), is marked by strong occurrences of boreal pollen taxa (especially Picea-Abies). Considering their spatial distribution and the coalescence of the British and Scandinavian ice sheets into the North Sea during the Last Glacial Maximum, these taxa probably originated from the North European Plain, i.e., eastern FM tributaries (east of the Rhine River), where cool-humid conditions generally prevailed. Then, the second phase, i.e. the HS1-b interval (~16.8–14.7 ka BP), is characterized by a deceleration of the EIS retreat and the drop of boreal pollen values at site MD13–3438 further signing a less influence of the upstream FM drainage system and thus a better characterization of pollen sources related with western FM tributaries. Superimposed to these two HS1 main phases, pollen fluctuations are concomitant with sub-millennial variability in the EIS deglaciation intensity. During the early HS1 (HS1-a), we discuss two short-term increases in the ratio between deciduous trees (Quercus-Corylus-Alnus) and herbaceous plants (Plantago-Amaranthaceae-Artemisia). These events are coeval with phases of increasing dinocyst-based SST seasonality (i.e. through summer SST amplification). We associate these events with lower contribution of the upstream FM catchment as well as, possibly, atmospheric warming and regional sea-level positive oscillations. The HS1-b is composed of three main phases that appear more influenced by the downstream FM drainage system. HS1-b1 (16.8–16.3 ka BP) corresponds to the driest and coldest conditions west of the Rhine River. HS1-b2 (16.3–15.5 ka BP) is coeval with large arrivals of iceberg from the Hudson strait in the Bay of Biscay and thus likely to a major sea-level positive oscillation associated with a phase of FM valley reworking. HS1-b3 (15.5–14.7 ka BP) corresponds to persistent arid conditions that preceded the subsequent more humid conditions recorded from 14.7 ka BP at the start of the Bölling-Alleröd.
(Palaeogeography, Palaeoclimatology, Palaeoecology. vol. 655, n° 0031-0182, pp. 112512 (14p.), 01/12/2024)
GEO-OCEAN, UBS, IFREMER, INSU - CNRS, UBO EPE, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, EPHE, PSL, IPMA, CCMAR, UAlg
Central-Eastern Europe as a centre of Middle Ages extractive metallurgy
Bohemia to Greece is home to some of the richest ore deposits on earth, with archaeological evidence suggesting a long history of metal use. However, the exact timing and extent of past metal processing activities remains unclear. The Middle Ages and Early Modern period (c. 500-1800 common era (CE)) in Europe, saw the expansion of metal use at an unprecedented scale, continent-wide. Here we analysed rates of past atmospheric lead (Pb) deposition in six peat bogs from Romania, Serbia and Greece. We show that after 1000 CE, the redevelopment of central European mining industry was synchronous with Pb pollution in southeastern Europe, with the onset of metal pollution occurring in the area prior to central Europe. Therefore, southeastern Europe may have led regional mining developments, with technological advances rapidly shifting from east to west through the Middle Ages. This indicates how southeastern Europe should be included in future discussions of Middle Age metallurgy not simply as a contributor, but at times as a leader in metal production.
(Journal of Archaeological Science. vol. 172, n° 0305-4403, pp. 106093, 01/12/2024)
USV, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, ELTE, ELTE, MTA, MTA, ULB
An operational discontinuous Galerkin shallow water model for coastal flood assessment
Hydrodynamic modeling for coastal flooding risk assessment is a highly relevant topic. Many operational tools available for this purpose use numerical techniques and implementation paradigms that reach their limits when confronted with modern requirements in terms of resolution and performances. In this work, we present a novel operational tool for coastal hazards predictions, currently employed by the BRGM agency (the French Geological Survey) to carry out its flooding hazard exposure studies and coastal risk prevention plans on International and French territories. The model, called UHAINA (wave in the Basque language), is based on an arbitrary high-order discontinuous Galerkin discretization of the nonlinear shallow water equations with SSP Runge–Kutta time stepping on unstructured triangular grids. It is built upon the finite element library AeroSol, which provides a modern C++ software architecture and high scalability, making it suitable for HPC applications. The paper provides a detailed development of the mathematical and numerical framework of the model, focusing on two key-ingredients : (i) a pragmatic treatment of the solution in partially dry cells which guarantees efficiently well-balancedness, positivity and mass conservation at any polynomial order; (ii) an artificial viscosity method based on the physical dissipation of the system of equations providing nonlinear stability for non-smooth solutions. A set of numerical validations on academic benchmarks is performed to highlight the efficiency of these approaches. Finally, UHAINA is applied on a real operational case of study, demonstrating very satisfactory results.
(Ocean Modelling. vol. 192, n° 1463-5003, pp. 102447, 01/12/2024)
BRGM, CAGIRE, Inria, UPPA, LMAP, UPPA, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IMB, UB, Bordeaux INP, CNRS, IMAG, CNRS, UM, CARDAMOM, IMB, UB, Bordeaux INP, CNRS, Inria