HAL-BRGM, les publications scientifiques en libre accès du BRGM
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Regulatory Landslide Hazard Zoning in New Caledonia: Integrating Temporal Probability in a Quantitative Framework
No full textInternational audienceA project was launched to produce landslide hazard maps for several municipalities in New Caledonia within a regulatory framework. A quantitative strategy was adopted to document and combine susceptibility, runout/propagation, temporal probability over a reference period, and intensity classes to assess hazard. Operationally, the implementation followed a stepwise "building-block" workflow, integrating each term of the hazard equation one by one to ensure traceability and maintain interpretability for non-specialist end users. Particular attention is given to how temporal probability is introduced and propagated through the workflow, and to how this choice affects the final hazard classes. A complementary, more probabilistically consistent alternative is also presented: a pixel-wise Poisson conversion applied to the continuous WoE output prior to reclassification. A case-study comparison highlights the respective strengths and limitations of both approaches
Complementarity of Passive Sampling and Composite Aqueous Sampling to Assess PFAS Emissions in Industrial Wastewater
No full textInternational audienceThis study evaluates the capability of three passive samplers (PS) to enhance the monitoring of per- and polyfluoroalkyl substances (PFAS) in industrial wastewater. Effluent from a textile manufacturer, an industrial laundry, and a semiconductor facility (all ≥10,000 m3/a discharge) was sampled over the course of two work weeks. Passive sampling included a polar organic chemical integrative sampler (POCIS), a Speedisk sampler (SD), and a flow-through tube passive sampler (TPS), while an automated aqueous sampler obtained continuous composite wastewatersamples. Composite samples revealed fluctuating concentrations of up to 18 different PFAS (varying by site) with total loads from 0.12 mg/day (semiconductor manufacturer) to 8.8 mg/day (industrial laundry). Notably, the PS detected up to 19 additional PFAS compared to aqueous samples, revealing multiple representatives of legacy PFAS as well as precursor compounds (6:2 FTAB, 6:2 FTS), differing by site.Quantitative assessments from PS in the complex industrial matrices remained inconclusive and need further examination. This study highlights the in situ enrichment potential of PS as sensitive and low-maintenance qualitative tools. When applied in parallel, PS and continuous composite aqueous sampling offer complementary advantages and improved insight in qualitative and quantitative monitoring of PFAS emissions from industrial sources, with relevance for regulatory surveillance
HyPiT: A thermodynamic database for modeling geochemical systems up to high temperatures, pressures and salinities
No full textInternational audienceModeling water-rock interactions in underground environments requires the use of thermodynamic databases that account for the complexity of groundwater chemical compositions under relevant pressure and temperature conditions. A key issue concerning saline groundwaters is their high ionic strength, which are often not reliably calculated and calls for the use of specific thermodynamic approaches. Among such approaches, the Pitzer model appears to be one of the most promising. However, its applicability to underground fluids is limited by the fact that the values of its numerous parameters are only known for a subset of chemical systems and, more particularly, are often missing for trace elements and at temperatures other than 25 • C. This paper describes a new way to develop a relevant thermodynamic database to account for the trace elements in these types of deep environments. It combines two in-house databases: Thermoddem, which relies on the B-dot Extended Debye-Hückel activity model, and PhreeSCALE, which uses the Pitzer formalism. The resulting Hybrid Pitzer-Thermoddem (HyPiT) thermodynamic database (TDB) integrates a simplified Pitzer model to account for major and trace elements. Based on a series of recent works (Simoes et al., 2016, 2017a, 2017b), the Pitzer binary interaction parameters, β (0) and β (1) and their first derivative with respect to temperature (dβ (0) /dT and dβ (1) /dT) are determined for simulating the first order interactions between trace elements and major species. The HyPiT database is successfully applied to different geochemical systems relevant to underground environments. They include (i) the solubility of gypsum in NaCl and sea-type brines of varying ionic strength at temperatures between 0 and 25 • C, (ii) the solubility of barite in NaCl brines at 25, 60 and 80 • C, (iii) the solubility of calcite in 0.1 and 4 M NaCl brines for temperatures and pressures up 250 • C and 1450 bars, respectively, (iv) the solubility of amorphous silica up to 150 • C in various single electrolyte solutions, namely HCl, NaCl, MgCl 2 , HNO 3 , NaNO 3 , Na 2 SO 4 , and MgSO 4 . Particular attention is also given to the modeling of iron-bearing systems such as the speciation of Fe III in LiCl solutions up to 20 mol/k
Unraveling pyroclastic density current dynamics with multiparameter geophysical sensing
No full textInternational audienceDetecting, locating, and characterising the dynamics of destabilised volcanic material is critical for assessing the extreme hazards posed by volcanic mass flows, such as pyroclastic density currents. Geophysical measurements of these events may offer information otherwise hardly observable at close range. Here we investigate pyroclastic density current dynamics using a multiparameter approach that combines seismic, distributed acoustic sensing, and infrasound data with thermal and visible imagery, supported by numerical simulations. We focus on two events at Stromboli volcano, Italy, that occurred in October and December 2022. By comparing visible imagery with seismic energy and applying array processing techniques, we identify different flow volumes ( ~23.5 ± 9.5 × 10 3 m 3 and ~80 ± 9 × 10 3 m 3 , respectively) and velocities (33-42 m/s and 54-59 m/s, respectively). Simulations reveal that reproducing these velocities requires volume-dependent empirical friction angles ( ~27°a nd 21°), consistent with dry granular flow behaviour and friction weakening. These findings offer new insights into the use of distributed acoustic sensing for volcanic monitoring and underscore the value of integrating multiparameter data with modeling to better understand complex volcanic processes
Response of rock material properties of quartzose sandstones to wildfire: a case study from Bohemian Switzerland National Park, Czechia
No full textInternational audienceIn the summer of 2022, a devastating wildfire struck the Bohemian Switzerland National Park in Czechia. It not only had significant ecological and economic impacts but also altered the near-surface properties of the vastly exposed quartzose sandstones of Upper Cretaceous age. This, together with the loss of vegetation and altered composition of slope sediments, may influence the dynamics of sandstone rock pillars and increase their vulnerability to erosion and slope processes in the coming years. This work focuses on describing the rock material affected by the 2022 wildfire, investigating the effects of thermal shock and extreme heat under natural conditions. The research employs a multi-step framework encompassing in situ sampling, laboratory tests and GIS modelling to understand these changes and patterns comprehensively. Samples were collected from outcrops and free-lying blocks at three locations: Dlouhý, Pravčický, and Černý důl. A total of 37 drill cores were extracted, with 185 P-wave velocity measurements conducted to assess variations with depth. Additionally, 78 samples were prepared for Unconfined Compression Tests and Brazilian tensile strength tests, complemented by 156 P- and S-wave velocity measurements. Notably, the Brazilian specimens yielded more pronounced results, revealing significant differences in tensile strength between Dlouhý and Černý důl at varying depths. Given the perspective of recurring monitoring in protected areas such as the study site, the research applied ultrasonic methods to offer a practical tool for assessing post-fire rock quality while adhering to standard laboratory tests. Clear limitations in the heterogeneous material were identified, with values showing limited amplitude in rock strength decay. This work provides a peculiar case study offering insights into changes in the properties of rock materials in the presence of a major wildfir
L’avenir de la ressource en eau face aux changements climatiques dans les Pays de la Loire: Rapport spécial Eau
No full textEn Pays de la Loire, les évolutions climatiques transforment profondément le cycle de l’eau. La hausse des températures, l’augmentation de l’évapotranspiration et la modification du régime des précipitations accentuent les déficits estivaux, fragilisent la recharge des nappes et renforcent les tensions sur les cours d’eau. Dans le même temps, les risques d’inondation et de submersion demeurent, tandis que la qualité de l’eau reste un défi majeur pour les milieux et l’alimentation en eau potable.Ces effets ne s’expriment pas de manière homogène sur le territoire régional. Selon les bassins versants, les caractéristiques géologiques, l’occupation des sols et l’intensité des usages, la disponibilité de la ressource et les marges d’adaptation varient fortement. Derrière une apparente abondance, des déséquilibres structurels s’installent, rendant certains territoires plus exposés aux pénuries, aux conflits d’usages et aux dégradations écologiques. Une question centrale s’impose alors : comment adapter la gestion de l’eau sans aggraver les vulnérabilités existantes ?Ce rapport du GIEC des Pays de la Loire propose une analyse scientifique de l’avenir de la ressource en eau dans la région. Il éclaire les mécanismes à l’oeuvre, documente les vulnérabilités territoriales et identifie les leviers d’action mobilisables. Il rappelle que l’adaptation ne peut se limiter à des réponses ponctuelles, mais qu’elle suppose une transformation durable des pratiques, fondée sur la sobriété, la protection des milieux et une gouvernance capable d’anticiper les évolutions à venir
Land use and management intensity shape nitrogen cycling and microbial functions, driving environmental impacts in French urban soils
No full textInternational audienceUrbanization profoundly alters soil through changes in land use and management intensity, affecting both soil functions and microbial communities. These shifts can degrade soil fertility and disrupt ecosystem processes. This study investigates how different public urban land uses -including showcase gardens, parks, tree-covered areas, roadsides, residential zones, sports fields and unused areas-influence nitrogen dynamics and microbial functions. We used a multifaceted approach combining biogeochemical measurements (NH₄ + , NO₃ -, total N), functional assays (potential mineralization, potential nitrification, potential denitrification), and molecular techniques (functional gene abundances and bacterial community profiling using Illumina MiSeq). Results showed that land use significantly influenced nitrogen cycle processes. Showcase garden areas were characterized by elevated nitrate levels, driven by fertilization and higher nitrification activity, whereas denitrification and related gene abundances were higher in parks and roadside soils. Structural equation modeling (SEM) revealed that soil organic carbon was a major driver of denitrification in most of the land uses, and pH positively influenced the abundance of ammonia-oxidizing archaea (AOA), whereas soil water retention, often reduced in compacted soils, was negatively correlated with most nitrogen variables. In terms of bacterial communities, this study revealed that bacterial functions linked to the nitrogen cycle varied according to land use. Lightly managed areas harboured more nitrogen-fixing bacteria, while intensely managed areas showed a predominance of bacteria involved in nitrification. Furthermore, the absence of any significant correlation between the multiple stages of the nitrogen cycle (mineralization, nitrification, denitrification) in intensively managed areas suggested a breakdown in nitrogen cycling, probably linked to excessive aeration, tillage and low organic matter accumulation or to differences in organic matter decomposition and stability. These findings highlight the sensitivity of nitrogen cycling to urban land management. Crucially, the role of organic matter dynamics in this context requires deeper investigation
Integrating problem structuring methods with formal design theory: collective water management policy design in Tunisia
No full textInternational audienceGroundwater management, especially in Mediterranean regions such as Tunisia, is challenging due to diverse stakeholder interests and the arid climate, which makes the sustainability of water resources extremely difficult. This paper proposes an innovative approach to the design of decision and policy alternatives by combining Problem Structuring Methods (PSMs) and the participatory tool based on the Concept-Knowledge (C-K) theory, named Policy-Knowledge, Concepts, Proposals (P-KCP). In a multi-methodological perspective, using Cognitive Maps and Value Trees in combination with P-KCP, the study aims to innovatively generate alternatives to address the sustainability issue of the case study, namely collective groundwater management. The paper provides a practical and adaptable guide to fostering innovation for policy design and generation of alternatives. By bridging decision theory and design theory, the study addresses the methodological gap in alternatives generation and highlights the role of C-K theory for supporting innovative design processes. Integrating PSMs and C-K theory, the multi-methodology advocates participatory approaches to address complex sustainability challenges, provides an adaptable, replicable tool, and encourages the creation of unconventional solutions. Ultimately, this paper offers new collective practices for groundwater management, expanding the set of alternatives through the integration of PSMs and C-K theory and reflecting on the applied multi-methodology
Rôle de la variabilité spatio-temporelle de la couverture végétale sur la migration des cordons dunaires en Gironde
No full textInternational audienceLa détection et le suivi de la variabilité spatio-temporelle de la végétation dunaire sont déterminants afin de comprendre et anticiper les évolutions morphodynamiques des cordons dunaires. En comparaison avec d'autres régions européennes plus septentrionales, où la végétation dunaire est plus dense et dont les limites spatiales sont plus facilement identifiables, la végétation dunaire en Nouvelle-Aquitaine est plus éparse et sa détection et quantification représentent un défi scientifique. Une nouvelle méthode couplant l'imagerie satellitaire (Sentinel-2, 10 x 10 m) et l'utilisation d'un réseau de neurones (S2DR3) est présentée dans cette étude. Cette méthode permet d'obtenir une cartographie d'un indicateur de végétation (NDVI) à haute résolution spatiale (1 x 1 m) et de renouveler l'opération à une fréquence annuelle. L'évaluation des erreurs de géoréférencement (< 5 m) et de la cohérence spectrale des images satellite (0.73 < R < 0.86) a démontré la fiabilité de cette méthode, permettant d'analyser les variations spatio-temporelles de la végétation. Les résultats ont montré une diminution des valeurs de NDVI, de plus de moitié entre 2017 et 2024 avec de fortes disparités spatiales le long d'une section dunaire de 500 mètres située au nord de Carcans Plage (Gironde). En associant cette cartographie de la végétation avec des données topographiques (LiDAR aéroporté), des interactions entre la dynamique de végétation et les changements morphologiques ont pu être identifiées en mettant en évidence différents niveaux de couverture de végétation et de mobilité sédimentaire. Ces données offrent également de nouvelles perspectives, comme notamment leur intégration dans des modèles numériques morphodynamiques afin d'avoir une compréhension plus fine des interactions entre la végétation et la dynamique sédimentair
Vers une modélisation semi-distribuée pour la simulation des étiages : comparaison de quatre modèles hydrologiques sur le bassin de la Meuse française
No full textLes sécheresses sont une préoccupation croissante pour les gestionnaires de l’eau, avec la perspective d’événements plus sévères et plus fréquents. La bonne prévision de ces épisodes est cruciale pour en atténuer les conséquences. La modélisation hydrologique semi-distribuée, en découpant le bassin versant en mailles interconnectées, permet de modéliser des débits à des points jaugés et non jaugés et de prendre explicitement en compte les variabilités spatiales observées sur le bassin. Dans cette étude, quatre modèles semi-distribués sont mis en place sur le bassin de la Meuse à Chooz, territoire qui présente des caractéristiques géologiques, topographiques et météorologiques contrastées. À l’issue d’un exercice de calage commun, les modèles fournissent des résultats cohérents en termes de débits sur l’ensemble du bassin et comparables aux résultats de modélisations globales à l’exutoire à Chooz. Des biais analogues sont observés entre les modèles, pouvant refléter des limites structurelles communes, des incertitudes sur les mesures de débits ou sur les forçages météorologiques. L’exercice sur l’étiage 2022 met en évidence une variabilité des débits d’étiage simulés, liée notamment au choix du modèle et à la météorologie utilisée pour son calage. Une perspective de développement pour améliorer la simulation des étiages consiste à affiner la compréhension des stocks et des écoulements souterrains puis leur représentation dans les modèles hydrologiques