HAL-BRGM, les publications scientifiques en libre accès du BRGM
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Runoff and soil erosion modelling at catchment scale in a tropical volcanic Island (Martinique, Lesser Antilles)
No full textInternational audienceTerrigenous inputs from hillslopes to hydrosystems can alter the quality of Fort-de-France Bay’s waters and sediments and so the balance of ecosystems (notably the degradation of coral reefs). Depending on the intensity of rainfall episodes, terrigenous inputs increase the turbidity the bay’s water and potentially result in the arrival of pollutants (including pesticides) in coastal waters leading to the ban of certain coastal economic activities. Another major impact is land degradation in upstream watersheds, leading to the impoverishment of agricultural soils. Furthermore, there has been much less research in soil erosion and sediment transfer in these tropical volcanic island settings compare to other environments.In order to analyze the rate and the spatio-temporal dynamics of water and suspended particles fluxes, the objective of this study is to model runoff and erosion on the two main watersheds (100 and 65 km²) draining into the Fort-de-France Bay, including a variety of soil type, land use and morphology. The modelling approach was used to perform an in-depth analysis of runoff and erosion processes. Various hypotheses were tested at different scales, particularly on the genesis of runoff (hortonian or soil saturation), soil depth, soil percolation. etc. Our results suggest the importance of saturation processes in controlling flood event occurrence. Compared with more traditional soil erosion modelling studies, this study on large watersheds have also enabled us to analyze upscaling effects’ aspects.This calibrated runoff and erosion model will be used to simulate different management or remediation plan to reduce sediment exports to the bay. Management plan will deal with agricultural practices and soft hydraulic systems such as grass strips, hedges (planted with local or endemic plant species) or fascines
Assessing short- and long-term responses of biological soil Indicators for evaluating ecological rehabilitation strategies
No full textInternational audienceSoils are vital resources increasingly threatened by urbanisation, industrial activities, and land-use changes. In France, the “Zéro Artificialisation Nette” (ZAN) policy demonstrates a national commitment to limit land take and preserve soil functionality, aligning with European objectives such as the proposed European Soil Law. This legislation seeks to protect and restore soils across the continent, while the EU’s Mission “A Soil Deal for Europe” promotes practices to reduce degradation, enhance ecological resilience, support effective rehabilitation strategies, and develop harmonised monitoring frameworks. These initiatives underscore the urgent need for approaches that not only prevent soil degradation but also restore essential soil functions.Rehabilitation approaches are increasingly adopting nature-based solutions, leveraging ecological processes to restore soil functions such as nutrient cycling, water regulation, and carbon sequestration. Central to these efforts is the concept of soil functioning, which reflects the dynamic interactions sustaining these functions. Monitoring rehabilitation success relies on biological, chemical, and physical indicators, which provide insights into soil health and its capacity to support ecosystem services.Despite their importance, challenges remain in developing and standardising these indicators. The lack of consensus makes it difficult to compare findings across studies or align them with existing frameworks, complicating the evaluation of rehabilitation outcomes. Harmonised monitoring methodologies that integrate multidisciplinary indicators are essential for evidence-based practices and ensuring the success of nature-based solutions in restoring soil health.This study focuses on identifying biological and physicochemical indicators to assess the short- and long-term success of ecological rehabilitation strategies. Five strategies, representing a gradient of rehabilitation effort, were implemented on degraded soils: (M0) no rehabilitation, (M2) deep soil decompaction, (M1) and (M4) bio-technosoil with low-quality materials and either an accompanying or recovery seeding, and (M3) bio-technosoil with high-quality materials and accompanying seeding. These strategies were designed to examine the effects of different inputs and interventions on soil recovery.Soil refunctionalisation was assessed using biological indicators, proxies for ecological functions, and physicochemical indicators, determinants of these functions. Biological indicators included microbial biomass, enzymatic activities, and nematode community composition, while physicochemical indicators assessed soil organic matter content, texture, and pH. Measurements were conducted at three key time points: the initial stage of rehabilitation, short term (6 months to 2.5 years), and long term (7.5 years).Preliminary results indicate that biological indicators provide robust early signals of soil recovery, with microbial biomass and enzymatic activities (e.g., linked to sulfur and nitrogen cycling) increasing within the first months. Higher rehabilitation efforts (M3, M1, M4) demonstrated stronger responses, correlating with elevated fertility indicators such as nitrogen and carbon content. Furthermore, the (M3) bio-technosoil modality is particularly dominated by thermolabile organic carbon forms. However, long-term monitoring revealed a diminishing differentiation between strategies, as soil properties converged over time, regardless of initial rehabilitation intensity.These findings suggest that greater initial efforts, such as using richer bio-technosoils and more mature planting, lead to faster soil refunctionalisation. Yet, the observed convergence over time highlights the need to balance initial efforts with long-term outcomes, which could influence cost-effectiveness assessments and guide the selection of rehabilitation strategies. By considering both short- and long-term impacts, this study contributes to the development of effective and sustainable soil rehabilitation approaches
MANG@COAST: A spatio-temporal modeling approach of muddy shoreline mobility based on mangrove monitoring
No full textInternational audienceHighly dynamic wave-exposed muddy coasts harbouring mangrove ecosystems can be subject to both marked accretion and erosion depending on the complex interactions between mud and waves. We propose a multiscale modelling approach and empirical equations calibrated and integrated into a landscape dynamics model implemented on a mud-bank coast using the Ocelet language to simplify the complex processes driving seamangrove coastline dynamics and quantity them with 10 years of satellite observations of mangrove shoreline fluctuations.We find that fluctuations in seafront mangroves can be simulated with acceptable accuracy along 200 km of coastline. In the absence of mud banks, seasonal wave forcing resulted in erosion rates reaching 1100 m/y. Our findings indicate that wave energy can be reduced by 90% at all locations when the width of mud banks exceeds 2000 m in front of the mangroves. Finally, we discuss the potential of this modeling approach for anticipating coastal changes
Modélisation biogéochimique du comportement des polluants dans des résidus miniers phytostabilisés
No full textInternational audienceLa sécurisation des résidus d'exploitations minières représente un défi environnemental majeur. Le projet ANR oMIMo « Optimisation des stratégies de phytostabilisation des déchets miniers riches en arsenic (As) : prédiction des impacts sur l'eau et la biodisponibilité des polluants pour les plantes en lien avec les activités microbiennes » a pour objectif principal d'anticiper les impacts, incluant les flux d'arsenic et de métaux par infiltration, lors du développement de la phytostabilisation comme option opérationnelle en domaine minier. Par la combinaison d'approches expérimentales à plusieurs échelles et de développement de stratégies de modélisation originales, oMIMo fournira une méthodologie accompagnée de recommandations, incluant le type d'analyses pertinentes (géochimiques, minéralogiques et biologiques) à effectuer pour évaluer l'évolution à moyen et long terme des flux d'As et de métaux avec un modèle numérique
A decision-support tool for repurposing hydrocarbon wells for geothermal application in France
No full textInternational audienceThe opportunities and barriers relating to the conversion of hydrocarbon wells in France for the development of geothermal energy have been studied by Ineris and BRGM since several years, particularly following the promulgation of Law No. 2017-1839 of 30 December 2017 putting an end to the exploration and the exploitation of hydrocarbons in France. The law also provides for the study of the potential for repurposing hydrocarbon facilities for other uses of the subsoil and, in particular, the opportunities for developing geothermal energy projects.In this context, BRGM and Ineris have developed, with the support of the General Direction of Risk Prevention (DGPR), a decision-support tool for public authorities based on flowcharts to identify the eligibility of hydrocarbon wells for conversion to geothermal uses. The repurposing requires to verify several criteria as the well accessibility, the energy needs identified near the facility, the presence of geothermal resources, the technologies and energy exchange systems for exploiting these resources that can be developed, the well integrity (cementing and casings) and potential work to apply before repurposing, the environmental and operational risks associated with the conversion and the regulatory framework in France
Permanent magnets in wind turbines stock and flows in Europe until 2050
No full textInternational audienceRenewable energy sources, such as wind turbines (WT), are primordial to reduce the use of fossil energy while meeting the rising demand for electricity. Permanent magnets (PM) embedded in some wind turbine (WT) generators contain significant amounts of Neodymium (Nd) and Dysprosium (Dy), identified as critical raw materials (CRM) by the European Union (EU). The increased deployment of WTs in the coming decades to achieve decarbonisation objectives is likely to drive up demand for these and other CRMs. However, the EU lacks the capacity to manufacture PMs or mine Nd and Dy, and relies on their imports, mainly from China. To reduce its resilience on third countries and mitigate potential supply disruption along the value chain, the EU recently adopted CRM Act, which set objectives for increasing recycling of CRMs embedded in PMs.The present work showcases a material flow analysis (MFA) that tracks CRMs through the life cycle of the entire EU WT sector (both onshore and offshore), until the year 2050, at member state level. To the best of the author’s knowledge, this is the first study in Europe doing an inflow-driven model, based on historical data from existing wind farms up to 2023, combines with a stock-driven model for the period 2024-2050. The future period evaluates three distinct scenarios, each reflecting a specific level of ambition. The first one assumes a business-as-usual situation, whereby the current recycling capacities are followed while the second scenario entails an increase in recycling in Europe, driven by enhanced recycling capacities, through improved collection rates, and reduced waste sent to landfill or energy recovery facilities. Building on the hypotheses of this scenario, the third one aims to achieve a more circular economy by promoting extension of the lifetime and better repair, reused and replacement of components.The model furthermore integrates material intensities (MIs), from literature review, for seven different types of WTs, including their external cables and foundations, distinguishing between onshore and offshore wind parks. The change over time in the market of WTs types is based on EU projections.The lifetime of the turbines was modelled using data from EU wind parks, including both installed and decommissioned WTs. The results indicate that the actual lifetime of WTs often exceeds the theoretical lifespan announced by the manufacturers, with a dismantling rate of 60% of turbines after 25 years. This longer lifetime might challenge the recycling projects effectiveness due to a lack of PM reaching their end-of-life. The initial findings suggest that the quantity of rare earth elements (REE) in WT PM waste is lower than that found in WEEE. However, their volume is expected to increase over time. By 2030, it is estimated that over 300 tonnes of Nd and 40 tonnes of Dy may become available from dismantled WTs in EU. This quantity of REEs could potentially contribute to achieving the CRM act objective
Dégradation sonochimique d'acide perfluorooctanesulfonique (PFOS) dans une matrice aqueuse
No full textInternational audienceLe traitement par sonochimie d’eau ultrapure et dopée avec de l’acide perfluorooctanesulfonique (PFOS) est conduit en variant les différents paramètres opératoires (concentration en PFOS, température de la solution, densité de puissance, etc.). Le dispositif de sonochimie (générateurs de SinapTec) assure le suivi en temps réel des principaux paramètres, ce qui permet, en le combinant à des analyses calorimétriques, de calculer précisément l’efficacité énergétique de la dégradation/minéralisation du PFOS. La dégradation et la minéralisation ont été mesurées par chromatographie LC MS/MS et par chromatographie ionique, respectivement. La dégradation observée après 180 minutes de sonochimie varie entre 88 et 97 %. La dégradation maximale est observée pour la densité de puissance maximale (270 W L-1) et la fréquence maximale (500 kHz). La température, dans la gamme 25 – 35 °C, n’a pas d’effet significatif sur la dégradation ou la minéralisation. La consommation électrique par unité de volume, et pour un abattement de la concentration d’un facteur 10, est la plus basse rapportée dans la littérature à ce jour (d’un facteur 2), et s’élève à 750 kW h m-3. Bien que cette consommation reste élevée, ce travail montre que des gains d'efficacité très importants en termes de consommation d'énergie, le facteur limitant de cette méthode, sont réalisables. L’application de la technique à une matrice plus complexe (eaux souterraines polluées par un mélange de PFAS) fait l’effet de travaux en cours de finalisation
Evolution of the West African fold belts: Review, new geochronological data, new correlations and new geodynamic hypothesis
No full textInternational audienceSeveral synthetic papers have been published about the geological structure of the threeWest African fold belts (Rokelides, Bassarides and Mauritanides), which were attached to the western margin of the West African Craton. Owing to the paucity of radiometric ages, some orogens and tectonic events have previously been confused and little consensus exists regarding their geodynamic evolution. Matching previous geological geochronological and geophysic data with nine new radiometric U-Pb ages on zircon, allows us to propose a new geodynamic model. Apart from ages of Mesoproterozoic events, four different orogens have been distinguished: Pan-African I (ca. 900 to 640 Ma), Pan-African II (ca. 640 to 520 Ma), Mali-Rokel River (ca. 490 to 450 Ma) and Variscan (ca. 450 to 300 Ma). The pan-African I orogeny is characterized by a complex evolution, terminating with a subduction process to the West, including the formation of a volcanic arc and a collisional event between ca. 660 and 640 Ma. The pan-African II orogen corresponds to a subduction process to the East leading to the building of a new volcanic arc and the formation of a back-arc basin to the East. Thenewly evidencedMali-Rokel River orogenic event led to the formation of extensive intra-continental N-S directed basins. The latter were folded and thrusted before the deposition of early Palaeozoic molasses. In the course of the Variscan Orogeny the Palaeozoicbasins setting in Mauritania and Northern Senegal were deformed during the Carboniferous Pangaea assembly. These two later orogensare intra-continental in the area but likely linked to far-field oceanic subduction to the West.For each orogenic period in the belts there are contemporaneous sedimentary deposits on the West African Craton and, of course, related unconformities between them. These data have facilitated correlations between the West African Belts and with the belts setting in adjacent areas like the Appalachians to the West and the northern Brazilian belts to the Sout
Particulate transport in porous media at pore-scale. Part 1: Unresolved-resolved four-way coupling CFD-DEM
No full textInternational audienceComputational Fluid Dynamics - Discrete Element Method (CFD-DEM) is a powerful approach to simulate particulate flow in porous media at the pore-scale, and hence decipher the complex interplay between particle transport and retention. Two separate CFD-DEM approaches are commonly used in the literature: the unresolved (particle smaller than the grid cell size) and the resolved (particle bigger than the grid cell size) approach. In this paper, we propose a novel CFD-DEM coupling approach that combines both unresolved and resolved coupling. Our new modeling technique allows for the simulation of particulate flows in complex pore morphology characteristic of porous materials. It relies on an efficient searching strategy to find grid cells covered by the particles and on an appropriate calculation of the fluid-solid momentum exchange term. The robustness and efficiency of the computational model are demonstrated using cases for which reference solutions – analytical or experimental – exist. The new unresolved-resolved four-way coupling CFD-DEM is used to investigate pore-clogging and permeability reduction due to the sieving and bridging of particles
Benchmarking shoreline prediction models over multi-decadal timescales
No full textInternational audienceRobust predictions of shoreline change are critical for sustainable coastal management. Despite advancements in shoreline models, objective benchmarking remains limited. Here we present results from ShoreShop2.0, an international collaborative benchmarking workshop, where 34 groups submitted shoreline change predictions in a blind competition. Subsets of shoreline observations at an undisclosed site (BeachX) over short (5-year) and medium (50-year) periods were withheld from modelers and used for model benchmarking. Using satellite-derived shoreline datasets for calibration and evaluation, the best performing models achieved prediction accuracies on the order of 10 m, comparable to the accuracy of the satellite shoreline data, indicating that certain beaches can be modelled nearly as well as they can be remotely observed. The outcomes from this collaborative benchmarking competition critically review the present state-of-the-art in shoreline change prediction as well as reveal model limitations, facilitate improvements, and offer insights for advancing shorelineprediction capabilities