HAL-BRGM, les publications scientifiques en libre accès du BRGM
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Predicting beach profiles with machine learning from offshore wave reflection spectra
No full textInternational audienceTracking and forecasting changes in coastal morphology is vital for development, risk reduction, and overall coastal management. One challenge of current coastal research and engineering is to find a method able to accurately assess the bathymetry profile along the coast and key parameters such as slope and sandbars. Traditional bathymetry measurements are obtained through echo-sounding, which is time-consuming, hazardous and costly. Using a variety of simulated cases, we test the potential of machine learning and in particular Neural Networks to reconstruct the coastal bathymetry profile from offshore sensed waves, based on shore-based wave reflection. Features such as foreshore slope, curvature, sandbars amplitude and positions can be captured
Quelle évolution pour le phénomène de retrait-gonflement des argiles en France métropolitaine à horizon 2065 ?
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Lost in navigation? Ensuring living lab frameworks stay on course with local needs
No full textSource Agritrop Cirad (https://agritrop.cirad.fr/615244/) * Autres projets (id;sigle;titre): ;Santés-Territoires;(EU) Projet Santés-Territoires//International audienceParticipatory modeling approaches, particularly those rooted in Companion Modeling (ComMod), are often credited with initiating socio-environmental transformations. Examples from Zimbabwe (Perrotton et al. 2017) and Burkina Faso (Daré et Venot, 2016) illustrate how these methods have facilitated engagement between stakeholders, sometimes leading to institutional changes over extended periods. However, the effectiveness of such approaches is contingent on their alignment with local realities and pressing challenges. The question remains: who holds the compass in these participatory frameworks? Do researchers, institutions and players succeed in abandoning their agenda? A case study from the Lake Guiers region in Senegal highlights the tensions between knowledge production, local agency, and transformative action. After several years of engagement with local communities through participatory workshops, a pivotal moment occurred in different arena : when a doctoral student presented her findings on hazardous chemical pollutants in the lake's water, when allochtone populations spoke out against their refusal to respect fishing restrictions face to face with native fishermen (Delay et al. 2023). Unlike previous discussions on ecosystem management, which were perceived as peripheral to daily survival, this revelation directly impacted livelihoods, exposing communities to immediate and invisible risks. The local response—calls for awareness campaigns and regulatory interventions—raised deeper questions about the adequacy of conventional participatory approaches. How can living lab models move beyond knowledge dissemination towards tangible systemic transformation? How can scientific findings generate experiential urgency rather than passive information? Recent scholarship suggests that for knowledge to trigger action, it must engage stakeholders not just intellectually/abstract, but affectively — a concept referred to as "affective knowing" (Hertz et Bousquet 2025). This perspective challenges traditional scientific detachment and underscores the need for transformative science that actively catalyzes change rather than merely observing it. A more reflexive and adaptive governance model is necessary—one that situates knowledge within local dispositifs (assemblages of discourses, institutions, and power structures). Rather than assuming that participatory models inherently lead to transformation, they must be reconfigured to align with the strategic urgencies of a given territory. This shift demands a reconsideration of the role of scientists in participatory governance: are they facilitators, guides, or interveners? By embedding participatory models within affective and political landscapes, living labs in Senegal and beyond can become true engines of systemic change rather than passive spaces for stakeholder dialogue
Impact of water table fluctuations on the redistribution of light hydrocarbons
No full textInternational audienc
Urban Attenuation Lengths in City-Like Environments: Insights from 3D Numerical Simulations of Site–City Interaction
No full textInternational audienceEstimating seismic ground motion in urban environments requires consideration of site–city interaction effects, which involve coupling between incident seismic wavefields and kinematic and inertial interactions with buildings. Although both observational data and numerical simulations have addressed this issue, the attenuation of seismic waves in urban settings remains poorly understood. In this study, we use 3D numerical simulations to examine the evolution of the wavefield in urban-like environments for frequencies up to 12 Hz. The simulations are conducted using the spectral element method. The model consists of a layered half-space with a flat surface, where the shear-wave velocity of the upper layer is 200 m/s and that of the half-space is 650 m/s. The urban configuration includes 30 buildings, each 100 m in height with a footprint of 25 m in both the x and y directions spaced 100 m apart. The building foundations are modeled as blocks with a depth of 15 m and horizontal dimensions identical to the superstructure. We perform three sets of simulations considering (1) free-field conditions, (2) foundations only, and (3) full buildings. The attenuation of seismic waves with distance is quantified by the amplitude decay of the ballistic wavefield. Our results indicate that at high frequencies (>5 Hz), seismic wave attenuation is primarily governed by scattering, driven by interactions with the foundations acting as diffractors. At lower frequencies, attenuation is mainly controlled by the buildings’ dynamics, leading to energy band gaps at the resonant frequencies of the buildings. Furthermore, the scattering attenuation length is found to be of the same order as the spacing between foundations. Finally, by analyzing the spatial variability of the ground motion within the urban cluster, we observe that the distance at which ground motion becomes uncorrelated is determined by the urban attenuation length, which we introduce as the urban mean free path
Magnetotelluric evidence for a melt-rich magmatic reservoir beneath Mayotte
No full textInternational audienceThe exact nature of crustal magmatic reservoirs is elusive as they cannot be sampled in situ. The traditional view that magma chambers contain essentially molten material has recently been replaced by the transcrustal magmatic system (TCMS), in which reservoirs are mostly composed of immobile magmatic crystals with a minute fraction of more mobile melt1,2,3, creating a ‘magmatic mush’3. Eruptions are possible if a significant portion of melt segregates into melt-rich lenses within the mush reservoir1,2,3. The TCMS concept is, however, a default model essentially justified by the absence of clear geophysical signatures of melt-rich magma chambers1,4, and by the rare and tentative estimates of the melt fraction in the crustal storage zones based on geochemical and textural analysis of eruptive products5,6. Here we image a bright electrical conductor at 23 ± 1 km below sea level beneath Mayotte island that we interpret as a magmatic reservoir, based on laboratory measurements of Mayotte’s melt conductivity. This large magmatic reservoir (more than 200 km3) contains a high melt fraction (22–42%). Such a crystal-to-liquid ratio matches the reconstructed differentiation paths7,8,9 producing the melts that recently erupted at Mayotte. This reservoir is possibly connected to the system that fed the large submarine eruption of Fani Maoré in 2018–201
Linking Fe-Ca metasomatism and hydrothermal sulfide mineralization in mantle rocks: insights from geochemistry and thermodynamic modeling
No full textInternational audienceUltramafic-hosted seafloor massive sulfide deposits have been reported in present-day oceanic settings over the past thirty years. These deposits and their fossil on-land analogs represent potential important resources for Cu, Co, Ni, Zn. However, developing comprehensive genetic models for deep-seatedhydrothermal processes is hindered by limited seafloor observations and reliance on large-scale geophysical studies. To overcome this issue, one can examine fossil systems, where hydrothermal plumbing architecture may be preserved. The Platta nappe (Swiss Alps) preserves a Jurassic hydrothermal system (the Marmorera-Cotschen Hydrothermal System; MCHS), where Cu-Fe-Co-Zn-Ni mineralization is associated with coeval Fe-Ca silicates (ilvaite, hydro-garnet, and diopside). The MCHS is hosted in serpentinites, which have been exhumed along a Jurassic paleo-detachment —a fossil analog ofa large-scale exhumation fault that forms oceanic core complexes at slow-spreading ridges— juxtaposing basalts onto serpentinites. The serpentinized footwall has numerous mafic intrusions, and the mafic-ultramafic rock contacts served as pathways for ore-forming fluids. Petrographic analyses and thermodynamic modeling indicate that Fe-Ca metasomatism occurred between 300‒360°C and at relatively low fO2 (from Magnetite-Native Fe to Fayalite-Magnetite-Quartz buffers), likely coeval with early-stage serpentinization. The composition of Fe-Ca silicates (Co, Ni, and REE contents, measured by in situ LA-ICP-MS) points to heterogeneous geochemical reservoirs involved during fluid-rock interaction. The geochemical compositions of Fe-Ca silicates in barren assemblages indicate an ultramafic-dominated system, while Fe-Ca silicates in mineralized assemblages point to an open-system, involving fluids derived from both mafic and ultramafic rocks. Mineralogical and geochemical signatures of Fe-Ca silicates in the MCHS do not support genetic relationships with common rodingitization. Our results suggest that Fe-Ca metasomatism may be a widespread deep-seated alteration along mafic-ultramafic rock contacts or in mantle rocks modified through melt-rock interaction accompanying mantle exhumation. We acknowledge JdC Fellowship (FJC2021-047190-I), funded by MCIN/AEI/10.13039/501100011033 with EU Next Generation Funds and funding from project PID2022-136471NB-C21 “The role of ultramafic rocks and related rocks in the sulfur and water cycles and their implications for the redox state of subduction zones (RUSTED)”, funded byMCIN/AEI/10.13039/501100011033 and by the ESF+
Optimisation de l'étape d'oxydation du fer à pH acide d'un procédé de biolixiviation in situ
No full textInternational audienceLa biolixiviation est une technologie plus économique et écologique que les technologies pyrométallurgiques et hydrométallurgiques conventionnelles pour l'exploitation des minerais à faible teneur en métaux. Elle repose sur des processus biologiques naturels impliquant des bactéries acidophiles extrêmes (pH < 3) qui oxydent le fer ferreux et le soufre conduisant à la dissolution des minéraux sulfurés et la solubilisation des métaux critiques et stratégiques qu’ils contiennent. Dans le cadre du projet Horizon Europe XTRACT, il s’agit de l’implémenter in situ dans un gisement polymétallique (principalement Zn, Sn, Cu, In) souterrain. Dans ce cas, un lixiviant acide riche en FeIII est produit en bioréacteur par des bactéries acidophiles FeII-oxydantes, puis percole à travers la roche forée pour lixivier les métaux. L’objectif a été d’optimiser l’étape d’oxydation du FeII. Une colonne (400 mL) a été opérée en continu après une phase en batch de colonisation du support (coupons de nylon) par Leptospirillum ferriphilum, autotrophe FeII oxydant obligatoire issu du consortium biolixiviant BRGM-KCC. La colonne a été alimentée par le bas avec un milieu de base à pH 1,2 contenant 9 g/L de FeII et de l’air enrichi en CO2 (1% v/v, source de carbone pour L. ferriphilum). Les paramètres suivants ont été testés pour mesurer leur impact sur le maintien d’une biomasse active, la consommation d’oxygène et de CO2, la vitesse d’oxydation du fer : diminution progressive du temps de séjour de 2,5 jours à 12h, retrait de coupons pour obtenir un régime hydrodynamique de type « airlift », transfert de gaz et % de CO2 injecté. Le but est d’identifier les paramètres limitants et d’optimiser la cinétique du procédé, prérequis nécessaire pour l’optimisation du procédé et son dimensionnement pour une implémentation sur site. Les paramètres testés ont permis d’oxyder 100% du FeII et d’atteindre un Eh très élevé, supérieur à 900 mV SHE, ce qui représente des conditions idéales pour l’étape suivante d’oxydation des minéraux sulfurés. Aucun lessivage de la biomasse n’a été observée malgré le temps de séjour très inférieur au temps de génération de L. ferriphilum (~24h)
Phytostabilisation des résidus miniers riches en arsenic : impact des activités microbiennes sur la mobilité et la biodisponibilité de l'arsenic et des métaux pour les plantes
No full textInternational audienceLa sécurisation des résidus miniers représente un enjeu environnemental majeur, et la phytostabilisation est une option à coût modéré pour atténuer l'érosion et la dispersion des particules contaminées. Dans le cadre du projet interdisciplinaire oMIMo (ANR-22-CE04-0012-0), un scénario contrôlé de phytostabilisation assistée a été étudié en serre en pots de 20 L, sur deux résidus riches en arsenic provenant d'anciennes mines d’argent et de plomb (Pontgibaud) et d'étain (Abbaretz). Les résidus, plantés ou non avec Festuca rubra, une herbacée présente sur les deux sites, ont été amendés avec du compost et du calcaire pour apporter des nutriments organiques aux plantes et réguler le pH et arrosés régulièrement avec de l'eau de source imitant la pluie naturelle. Le suivi des pots, réalisé tous les six mois sur deux ans, a combiné l'évolution de la communauté procaryote (abondance par NPP des bactéries oxydant ou réduisant As ou fer (Fe), oxydant le soufre (S) ou réduisant les sulfates (SO4) ; diversité de la communauté active par séquençage des ARNr 16S), de la géochimie de l’ eau interstitielle (pH, Eh, conductivité, chimie, spéciation de l'As et du Fe), et de la biodisponibilité et toxicité de l'As et des métaux pour les plantes (teneur en As et métaux dans les feuilles, indice oméga-3). Les principaux résultats montrent que Festuca rubra s’est développée dans les résidus amendés. Les abondances par NPP ont montré une cohabitation des bactéries oxydantes et réductrices ciblées. La diversité de la communauté procaryote active, dominée par des bactéries du compost à T0, a évolué différemment selon le résidu, avec cependant une dominance des Cyanobacteria qui se développent à la surface des pots. Fe et As, essentiellement sous forme d’AsV, ont été mobilisés dans l’eau porale du résidu Abbaretz, phénomène probablement lié à l’activité des bactéries FeIII- et AsV-réductrices dont l’abondance a augmenté à six mois dans ce résidu, alors qu’As et Fe sont restés piégés dans le résidu Pontgibaud. L’évolution sur deux ans de l’ensemble des paramètres géochimiques et biologiques doit apporter une compréhension plus approfondie des mécanismes (notamment microbiens) influençant le devenir de l'As et des métaux dans les résidus, leur impact sur les plantes, l'objectif final étant, à terme, de développer un modèle de transport réactif pour prédire la mobilité et la disponibilité de l'As et des métaux pour les plantes dans les déchets miniers phytostabilisés riches en A
Modeling Complex Flows In Porous Media With ComPASS
No full textInternational audienceComPASS [1] is an open-source, massively parallel simulator for multi-phase, multi-component flow,designed with a mixed-dimensional approach to accurately model 3D porous media, 2D fractures, and1D wells. All domains are discretized on a shared unstructured (typically polyhedral) mesh: porousmedia are represented by mesh elements (3D), fractures by mesh faces (2D), and wells by mesh edges(1D). Modeling of underground systems strongly benefits from the use of unstructured meshes sincethe latter can handle arbitrary geometries. Spatial discretization is based on the Vertex ApproximateGradient (VAG) finite volume scheme, a scheme designed to be very efficient (accuracy vs number ofdegrees of freedom) on polyhedral meshes. Moreover, this scheme has been carefully adapted to enablerobust coupling between the mixed-dimensional features.Initially developed for simulating complex geothermal systems [2], ComPASS has since been extendedto applications in hydrology and gas storage. Ongoing developments aim to integrate additional physicalprocesses, such as geomechanics and chemical reactivity, further enhancing the simulator’s capabilities.---[1] https://gitlab.com/compass[2] A. Armandine Les Landes, L. Beaude, D. Castanon Quiroz, L. Jeannin, S. Lopez, et al., Geothermal modeling incomplex geological systems with ComPASS. Computers Geosciences, 194, pp.105752 (2025