78 research outputs found
Mise en oeuvre d'un outil d'alerte et de cartographie temps réel des aléas naturels liés aux précipitations dans les régions montagneuses et méditerranéennes du Sud-Est de la France
International audienceDue to its mountainous topography and its Mediterranean climate, the Provence-Alpes-Côte d'Azur (PACA) region in Southeastern France is particularly prone to flash floods, debris flows and mass movements (landslides and rockfall). A mapping system for these rainfall induced hazards has been tested by local and regional authorities and Government agencies since 2011 as part of the RHYTMME project. This system allows, thank to radar rainfall estimation and rainfall-runoff modelling, the real-time warning and monitoring of flash floods wherever they may occur in the PACA territory. It is also intended to enable, during intense rainfall events, the localisation of the streams susceptible to generate debris flows and of the slopes the more likely to trigger landslides and/or rockfalls
New Gripping and Binding Device Greatly Improves Preparation of Natural Clasts for RFID Tracking
Soil and water bioengineering: practice and research needs for reconciling natural hazard control and ecological restoration
Soil and water bioengineering is a technology that encourages scientists and practitioners to combine their knowledge and skills in the management of ecosystems with a common goal to maximize benefits to both man and the natural environment. It involves techniques that use plants as living building materials, for: (i) natural hazard control (e.g., soil erosion, torrential floods and landslides) and (ii) ecological restoration or nature-based re-introduction of species on degraded lands, river embankments, and disturbed environments. For a bioengineering project to be successful, engineers are required to highlight all the potential benefits and ecosystem services by documenting the technical, ecological, economic and social values. The novel approaches used by bioengineers raise questions for researchers and necessitate innovation from practitioners to design bioengineering concepts and techniques. Our objective in this paper, therefore, is to highlight the practice and research needs in soil and water bioengineering for reconciling natural hazard control and ecological restoration. Firstly, we review the definition and development of bioengineering technology, while stressing issues concerning the design, implementation, and monitoring of bioengineering actions. Secondly, we highlight the need to reconcile natural hazard control and ecological restoration by posing novel practice and research questions
A high-frequency, long-term data set of hydrology and sediment yield: the alpine badland catchments of Draix-Bléone Observatory
Draix-Bléone critical zone observatory was created in
1983 to study erosion processes in a mountainous badland region of the
French Southern Alps. Six catchments of varying size (0.001 to 22 km2)
and vegetation cover are equipped to measure water and sediment fluxes, both
as bedload and suspended load. This paper presents the core dataset of the
observatory, including rainfall and meteorology, high-frequency discharge
and suspended-sediment concentration, and event-scale bedload volumes. The
longest records span almost 40Â years. Measurement and data-processing
methods are presented, as well as data quality assessment procedures and
examples of results. All the data presented in this paper are available on
the open repository https://doi.org/10.17180/obs.draix (Draix-Bleone
Observatory, 2015), and a 5-year snapshot is available for review at
https://doi.org/10.57745/BEYQFQ (Klotz et al., 2023).</p
Simple large wood structures promote hydromorphological heterogeneity and benthic macroinvertebrate diversity in low-gradient rivers
This work has been carried out within the SMART Joint Doctorate Programme ‘Science for the MAnagement of Rivers and their Tidal systems’ funded by the Erasmus Mundus programme of the European Union
(trad auto)Géomorphologie et transport sédimentaire des systèmes fluviaux alpins : des torrents à forte pente aux rivières à lit de gravier du piémont
This report proposes a synthesis of my research activity since my assignment at the ETNA research unit of Irstea Grenoble. My works concern the geomorphology and sediment transport of alpine rivers, from steep-slope headwaters to large gravel-bed piedmont rivers. They can be structured around three thematic fields that are presented as successive chapters in the present report. The first chapter is dedicated to the geomorphic responses of headwaters. Results concerning the regional detection of the most dangerous debris-flow prone torrents are presented, as well as outcomes concerning rainfall triggering conditions of debris flows, coming from recently deployed monitoring stations in the French Alps. The second chapter deals with the sediment supply effect on channel forms and sediment transport processes. The debris-flow sediment cascade of a bedrock-dominated catchment of the Northern Prealps is analysed through intensive and repetitive topographic surveys of hillslopes and channels. The sediment supply effect on bedload responses has been investigated in a small experimental catchment at Draix, where a seasonal hysteresis has been detected and interpreted as a consequence of periodic sediment pulses from hillslopes. The longterm morphological trajectories of alpine braided rivers were reconstructed and confronted to present-day sediment supply conditions in the French Alps. The third chapter concerns bedload transport assessment and monitoring in alpine environments. Examples of applications of (1) repetitive airborne LiDAR imagery for sediment budget reconstruction of a large braided channel, (2) passive RFID tags for the tracing of bedload transport along a high sediment load torrent, and (3) automatic bedload slot-sampler under conditions of ultra-high suspended sediment concentrations are successively presented. The last chapter presents research perspectives of the three thematic fields for the next 5 years. My activities in term of research animation are presented in the last part of the report.Ce rapport présente une synthèse des travaux que j'ai réalisé depuis mon affectation au sein de l'unité de recherche ETNA de l'Irstea de Grenoble. Ils portent sur la géomorphologie et le transport solide des rivières alpines, depuis les têtes de bassin à fortes pentes jusqu'aux corridors fluviaux de piémont. Ces travaux sont structurés autour de trois axes thématiques, qui sont présentés successivement sous forme de chapitres. Le premier chapitre est consacré aux réponses géomorphologiques des têtes de bassin. Il présente les résultats obtenus en matière de détection régionale des torrents susceptibles de produire des laves, et en matière de caractérisation des conditions pluviométriques de déclenchement des laves étudiées à partir de stations expérimentales déployées récemment dans les Alpes. Le deuxième chapitre s'intéresse aux effets de la recharge sédimentaire sur les formes et les flux solides. La cascade sédimentaire associée aux événements de lave survenus dans un bassin rocheux des Préalpes du Nord est présentée à partir des résultats d'un suivi topographique répétitif et intensif des versants et des chenaux torrentiels. L'effet de la recharge sédimentaire du lit sur le transport solide par charriage a été étudié sur le site du Moulin à Draix, où nous avons mis en évidence une hystérèse saisonnière du flux charrié sous l'effet de la propagation de vagues sédimentaires annuelles. La recharge sédimentaire est aussi appréhendée à l'échelle des tresses alpines, dont les trajectoires morphologiques ont été reconstituées à partir de données historiques et confrontées aux conditions actuelles de fourniture sédimentaire. Le troisième chapitre concerne la mesure du transport solide par charriage en contexte alpin, à partir d'approches innovantes. Des exemples d'application de l'imagerie LiDAR aéroportée en contexte de lit en tresses, du traçage par RFID de la charge de fond en contexte torrentiel, et de la mesure haute-fréquence du charriage à l'aide d'une trappe à fente en contexte de forte concentration en fines, sont présentés successivement. Le dernier chapitre présente les perspectives de recherche à 5 ans pour chaque thème de recherche. Mon expérience en matière d'animation de la recherche est présentée de manière factuelle en fin de mémoire
La mobilité de la charge de fond des rivières torrentielles méditerranéennes
[Departement_IRSTEA]RE [TR1_IRSTEA]RIE / ALPRISKNational audienceEvent-based bedload mobility of three tributaries to the Drôme River (Barnavette, Béoux and Esconavette) was monitored between 1997 and 2002 by means of field devices allowing the measurement of scour and fill processes and individual particles displacements. Three field sites including one or two resurveyed cross sections, a set of scour chains, painted tracers and one crest stage gauge were installed near the outlet of the streams. This equipment allowed the characterization of the frequency of bedload transport, the hydraulic conditions for incipient motion and the distances of transport of individual grains. We observed that an average of 6 to 7 competent flow events per year occurred during the study period. The annual distances of transport of coarse particles range between 450 and 470 m. The thresholds of motion for bedload transport are similar to the values published for small gravel-bed rivers, with dimensionless critical shear stress between 0,031 and 0,076.La mobilité de la charge de fond de trois affluents de la Drôme (Barnavette, Béoux et Esconavette) a fait l'objet d'un suivi événementiel entre 1997 et 2002, au moyen d'un dispositif de terrain relativement simple permettant de mesurer les phénomènes de creusement et de remblaiement du lit ainsi que la mise en mouvement des particules. Trois stations de mesure comprenant un ou plusieurs profils en travers pour le suivi topographique, un ensemble de chaînes d'érosion, des traceurs colorimétriques (particules peintes) et un équipement d'enregistrement des hauteurs d'eau maximales ont été installées à proximité de l'exutoire des trois affluents. Cet équipement a permis de caractériser : (1) la fréquence du charriage (6 à 7 crues mobilisatrices par an en moyenne), (2) les distances de transport de la charge de fond (en moyenne entre 450 et 470 m par an), (3) les seuils de mise en mouvement. Ceux obtenus ici sont en adéquation avec les valeurs communément observées dans les rivières à forte pente, avec des forces tractrices critiques adimensionnelles comprises entre 0,031 et 0,076
Sediment dynamics in Alpine basins
International audienceThe special issue consists of 13 papers. The 13 papers can be grouped according to the following four main themes: i) Sediment cascade and budget in steep headwater catchments; ii) Bedload transport monitoring in Alpine streams and rivers; iii) Effects of structures on sediment transport continuity: characterization and restoration; and iv) Tools and approaches for sediment management in Alpine basins
Active channel width as a proxy of sediment supply from mining sites in New Caledonia
International audienceAlthough the channel morphology of upland fluvial systems is known to be strongly controlled by sediment supply from hillslopes, it is still difficult to isolate this effect from the other controlling factors of channel forms, such as the sediment transport capacity (depending notably on the size of the catchment) and local conditions (e.g. confinement, riparian vegetation, valley-floor slope). The rivers in New Caledonia offer an interesting field laboratory to isolate the morphological effect of contrasted sediment supply conditions. Some of these rivers are known to be highly impacted by the coarse sediment waves induced by the mining of nickel deposits that started in the early 1870s, which was particularly intensive between the 1940s and 1970s. The propagation of the sediment pulses from the mining sites can be traced by the presence of wide and aggraded active channels along the stream network of nickel-rich peridotite massifs. A first set of 63 undisturbed catchments in peridotite massifs distributed across the Grande Terre was used to fit a classic scaling law between active channel width and drainage area. A second set of 86 impacted sites, where the presence of sediment waves was clearly attested by recent aerial imagery, showed systematically wider active channels, with a width ratio around 5 (established from the intercept ratio of width-area power laws). More importantly, this second set of disturbed sites confirmed that the residual of active channel widths, computed from the scaling law of undisturbed sites, is statistically positively related to the catchment-scale relative area of major mining sediment sources. It is therefore confirmed that the characterization of sediment supply conditions is crucial for the understanding of spatial patterns of active channel width, and this should be more thoroughly considered in morphological studies of rivers draining environments with contrasted geomorphic activities on hillslopes
Debris-flow susceptibility of upland catchments
International audienceOver the last three decades, many regional studies in mountain ranges under temperate climate revealed that it is possible to discriminate debris-flow and fluvial fans from morphometric indicators measured at the scale of the catchment and the fan itself. The most commonly used indicators are the Melton index (R), a normalized index of the gravitational energy of the catchment, and the fan slope (S). A wide range of thresholds have been proposed for discriminating purpose, but these are generally based on a small population of catchments and may be highly influenced by ambiguous fans included in the data set. A database of 620 upland catchments from several mountain ranges under temperate climate was compiled from the literature to propose robust discriminant morphometric thresholds for debris-flow versus fluvial responses. Linear discriminant analysis (LDA) and logistic regression (LR) were performed using the whole data set, and a leave-one-out cross-validation was used to evaluate performances of the models. Sensitivity and specificity scores obtained for LDA and LR were 0.96 and 0.73, and 0.95 and 0.75, respectively. It is also shown that the channel slope above which debris-flow is observed decreases with the gravitational energy of the catchment. Limitations of the morphometric discrimination are discussed
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