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2. Tipping points in hydrology: observed regional regime shift and System Dynamics modeling

Author

Wendling, Valentin, Peugeot, Christophe, Grippa, Manuela, Kergoat, Laurent, Mougin, Eric, Hiernaux, Pierre, Rouché, Nathalie, Panthou, Geremy, Rajot, Jean-Louis, Pierre, Caroline, Mora, Olivier, Garcia-Mayor, Angeles, Ba, Abdramane, Lawin, Emmanuel, Bouzou-Moussa, Ibrahim, Demarty, Jerôme, Etchanchu, Jordi, Hector, Basile, Galle, Sylvie, Lebel, Thierry, Project, Tiphyc, Hydrosciences Montpellier (HSM), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Montpellier (UM), Géosciences Environnement Toulouse (GET), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Institut des Géosciences de l’Environnement (IGE), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP ), Université Grenoble Alpes (UGA), Institut d'écologie et des sciences de l'environnement de Paris (iEES Paris ), Institut de Recherche pour le Développement (IRD)-Sorbonne Université (SU)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Délégation à l'Expertise scientifique collective, à la Prospective et aux Etudes (UAR), Institut National de la Recherche Agronomique (INRA), Utrecht University [Utrecht], Institut National de L’Eau, Cotonou, Université Abdou Moumouni [Niamey], Université des Sciences, des Techniques et des Technologies de Bamako (USTTB), ANR : Exploring tipping points in the West African hydrological cycle – TipHyc, and ANR-20-CE01-0014,TipHyc,Exploration des points de bascule dans le cycle hydrologique ouest-africain(2020)

Subjects
[SDE.MCG]Environmental Sciences/Global Changes, [NLIN]Nonlinear Sciences [physics], [SDU.STU.HY]Sciences of the Universe [physics]/Earth Sciences/Hydrology, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment
Abstract

River runoff and climate data existing from 1950 to present time in West Africa are analyzed over a climatic gradient from the Sahel (semi-arid) to the Gulf of Guinea (humid). The region experienced a severe drought in the 70s-90s, with strong impact on the vegetation, soils and populations. We show that the hydrological regime in the Sahel has shifted: the runoff increased significantly between pre- and post-drought periods and is still increasing. In the Guinean region, instead, no shift is observed. This suggests that a tipping point could have been passed, triggered by climate and/or land use change. In order to explore this hypothesis, we developed a System Dynamics model representing feedbacks between soil, vegetation and flow connectivity of hillslopes, channels and aquifers. Model runs were initialized in 1950 with maps of land use/land cover, and fed with observed rainfall (climate external forcing). The modeling results accurately represent the observed evolution of the hydrological regime on the watersheds monitored since the 50s (ranging from 1 to 50000 km²). The model revealed that alternative stable states can exist for the climatic conditions of the study period. From the model runs, we showed that the drought triggered the crossing of a tipping point (rainfall threshold), which explains the regime shift. We identified domains within the watersheds where tipping occurred at small scale, leading to larger scale shifts. This result supports that tipping points exist in semi-arid systems where ecohydrology plays a major role. This approach seems well suited to identify areas of high risk of irreversible hydrological regime shifts under different climate and land-use scenarios.

Published
2022

4. Drought-induced regime shift and resilience of a Sahelian ecohydrosystem

Author

Wendling, Valentin, Peugeot, Christophe, Mayor, Ángeles Garcia, Hiernaux, Pierre, Mougin, Eric, Grippa, Manuela, Kergoat, Laurent, Walcker, Romain, Galle, Sylvie, Lebel, Thierry, Spatial Ecology and Global Change, Environmental Sciences, Hydrosciences Montpellier (HSM), Institut de Recherche pour le Développement (IRD)-Université Montpellier 2 - Sciences et Techniques (UM2)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Copernicus Institute for Sustainable Development, Utrecht University [Utrecht], Géosciences Environnement Toulouse (GET), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Université Fédérale Toulouse Midi-Pyrénées-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS), Laboratoire Ecologie Fonctionnelle et Environnement (ECOLAB), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées, Laboratoire d'étude des transferts en hydrologie et environnement (LTHE), Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique de Grenoble (INPG)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA), Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement (IRD)-Université Montpellier 2 - Sciences et Techniques (UM2)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut Ecologie et Environnement (INEE), Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), Institut des Géosciences de l’Environnement (IGE), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP ), Université Grenoble Alpes (UGA), Institut de Recherche pour le Développement (IRD)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019]), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Laboratoire Ecologie Fonctionnelle et Environnement (LEFE), Institut Ecologie et Environnement (INEE), Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université de Toulouse (UT), Spatial Ecology and Global Change, and Environmental Sciences

Subjects
010504 meteorology & atmospheric sciences, rainfall, Climate change, alternative stable states, 010501 environmental sciences, 01 natural sciences, Alternative stable state, Soil retrogression and degradation, Sahel, Clearing, Ecosystem, Regime shift, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences, General Environmental Science, 2. Zero hunger, regime shifts, rainfall variability, Renewable Energy, Sustainability and the Environment, variability, Public Health, Environmental and Occupational Health, Vegetation, 15. Life on land, 13. Climate action, Climatology, [SDE]Environmental Sciences, eco-hydrology, Environmental science, Surface runoff
Abstract

International audience; The Sahel (a semi-arid fringe south of the Sahara) experienced a long and prolonged drought from the1970s to the mid-1990s, with a few extremely severe episodes that strongly affected ecosystems andsocieties. Long-term observations showed that surface runoff increased during this period, despite therainfall deficit. This paradox stems from the soil degradation that was induced by various factors,either directly linked to the drought (impact on vegetation cover), or, in places, to human practices (land clearing and cropping). Surface runoff is still increasing throughout the region, suggesting that Sahelian ecohydrosystems may have shifted to a new hydrological regime. In order to explore this issue, we have developed a simple system dynamics model incorporating vegetation–hydrology interactions and representing in a lumped way the first order processes occurring at the hillslope scale and the annual timestep. Long term observations on a pilot site in northern Mali were used to constrain the model and define an ensemble of plausible simulations. The model successfully reproduced the vegetation collapse and the runoff increase observed over the last 60 years. Our results confirmed that the system presents two alternative states and that during the drought it shifted from a high-vegetation/low-runoff regime to the alternative low-vegetation/high-runoff one, where it has remained trapped until now. We showed that the mean annual rainfall deficit was sufficient to explain the shift. According to the model, vegetation recovery and runoff reduction are possible in this system, but the conditions in which they could occur remain uncertain as the model was only constrained by observations over the collapse trajectory. The study shows that the system is also sensitive to the interannual and decadal variability of rainfall, and that larger variability leads to higher runoff. Both mean rainfall and rainfall variability may increase in central Sahel under climate change, leading to antagonist effects on the system, which makes its resilience uncertain.

Published
2019

7. Development of a suspended aggregates and flocs carracterisation system

Author

Wendling, Valentin, Laboratoire d'étude des transferts en hydrologie et environnement (LTHE), Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique de Grenoble (INPG)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA), Laboratoire d'étude des transferts en hydrologie et environnement (Grenoble), Université Grenoble Alpes, Nicolas Gratiot, Cédric Legout, Institut National Polytechnique de Grenoble (INPG)-Centre National de la Recherche Scientifique (CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS), and STAR, ABES

Subjects
Transport en suspension, Développement instrumental, Instrumental development, Flocculation, [SDU.STU]Sciences of the Universe [physics]/Earth Sciences, Vitesse de chute, Mesure optique, Optical measurement, Cohesive sediment, Sellting velocity, Floculation, [SDU.STU] Sciences of the Universe [physics]/Earth Sciences, Sédiments cohésifs, Suspended sediment transport
Abstract

Little is known about the processes that govern the evolution of suspended particle characteristics during their transport through a river basin. This is a main limitation for modelling erosion severity or suspended solids (SS) fluxes. It also leads to difficulties to propose management policies adapted to environmental legislation. Based on experiments in controlled environments, we have shown that soil particles tend to disaggregate in turbulent flows. The increase in SS concentration was associated to an increase of the disaggregation of SS particles, leading to smaller final particle sizes. Laboratory experiments also showed that the variability of the particle sizes due to their evolution over one hour was smaller than the variability due to the soil type from which the particles originated. However it is important to ensure that the suspended particles behave in the same way in natural conditions, where complex interactions between hydraulic, chemical and biological processes can influence their evolution. Up to now no measurement method allows measuring continuously the suspended sediment properties in highly concentrated fluids (from one to hundreds grams per liter), such as those observed in headwater catchments during runoff events. This severely limits the possibility to identify the processes that are important to consider in numerical models. The Aggregate and Floc Characterization System (SCAF) has been developed in order to measure SS properties for a wide range of SS concentrations. It was designed to be easily incorporated into sequential samplers. Immediately after the collection of a sample from the river, the sedimentation of the suspension is recorded by continuous measurements of the absorbance by a series of optical sensors. A method was proposed to processes the raw optical data in order to obtain the settling velocity distribution of the suspension. It also provides a flocculation index representing the tendency of the particles to flocculate during their sedimentation. The calculated settling velocity distributions were validated on a large range of materials and settling regimes in order to cover the natural variability of suspended sediments. For sediments that hardly flocculate during their sedimentation or are non-cohesive, the measurements of the SCAF were similar to those from other methods. In the case of suspensions that strongly flocculate during sedimentation, most of the classical methods give non-representative falling velocities. In this case, the optical property of the particles may vary during settling, affecting the optical measurement. The proposed method allowed quantifying the increase of settling velocity induced by flocculation, and provided confidence intervals for the settling velocities. For high SS concentrations ( > 10 g/l), a settling front can be formed during the sedimentation, which is well characterized by the SCAF. The measurement of the settling velocity distributions and of the flocculation index can be used to identify different particle populations (sand grains, flocs, individual particles) forming a suspension. Monitoring these properties in watersheds offers new insights to explore sediment connectivity within river basins and to optimize water management strategies., L'évolution des caractéristiques des particules en suspension au cours de leur transfert au sein des bassins versants est encore mal connue. Ceci limite actuellement notre aptitude à prédire correctement l'érosion ou les flux de matières en suspension (MES) et rend difficile la proposition de pratiques de gestion adaptées aux réglementations en vigueur. A partir d'expériences en milieu contrôlé, nous avons montré que les particules de sols ont tendance à se désagréger en milieu turbulent. Il semble de plus qu'une augmentation de la concentration en suspension accélère cette désagrégation et conduise à des particules plus fines. Même si l'évolution des particules à l'échelle horaire semble rester de second ordre derrière les caractéristiques des sols sources, il est indispensable de pouvoir vérifier si les particules en suspension se comportent de la même manière en conditions naturelles où des interactions complexes entre processus peuvent avoir lieu. Cependant l'absence de méthode de mesure permettant le suivi des propriétés de transport des sédiments en écoulements très concentrés (de 1 plusieurs centaines de grammes par litre) dans les bassins élémentaires limite notre capacité à hiérarchiser les processus à considérer pour modéliser le transfert sédimentaire ou améliorer la gestion opérationnelle des sédiments. Afin de répondre à ce besoin instrumental, nous avons développé un Système de Caractérisation des Agrégats et des Flocs (SCAF). Cet instrument est conçu pour être incorporé dans les stations de suivi hydro-sédimentaire. La mesure est réalisée immédiatement après prélèvement d'un échantillon de la suspension à caractériser par une série de capteurs optiques qui suivent l'évolution de l'absorbance optique durant la sédimentation de l'échantillon. Nous proposons une méthode de traitement des données optiques donnant accès à la distribution des vitesses de chute de la suspension ainsi qu'à un indice de floculation qui renseigne sur la capacité des MES à floculer durant leur sédimentation. Les distributions de vitesses de chute mesurées sont validées sur une large gamme de matériaux et de régimes de sédimentation, afin de couvrir la variabilité des types de matériaux et des concentrations observées en milieu naturel. Pour des sédiments non cohésifs ou floculant peu durant leur sédimentation les mesures du SCAF s'ajustent sur celles issues des autres méthodes. Pour les suspensions qui floculent durant leur sédimentation, la plupart des méthodes de mesure classiques conduisent à des vitesses de chute non représentatives de la suspension. Nous avons montré que les variations des propriétés optiques des matières en suspension lors de leur floculation impactent nos mesures. La méthode proposée permet cependant de quantifier l'augmentation des vitesses de chute avec la floculation, et d'encadrer l'incertitude des mesures. Pour les mesures à forte concentration (>10 g/l), un front d'entravement peut se former durant la sédimentation, le SCAF mesurant alors précisément les vitesses de chute du front. La mesure des distributions des vitesses de chute et de la cohésion des particules en suspension peut permettre d'identifier différentes populations de particules formant une suspension (grains de sables, flocs, matières fines...). Le suivi de telles informations au sein de bassins versants ouvre de nouvelles perspectives pour aborder la connectivité sédimentaire et s'orienter vers une gestion optimale des flux de MES.

Published
2015

8. Small scale eco-hydrological regime shifts and impacts on regional changes in the Sahel.

Author

Wendling, Valentin, Peugeot, Christophe, Mayor, Angeles Garcia, Hiernaux, Pierre, Mougin, Eric, Walcker, Romain, Grippa, Manuela, Kergoat, Laurent, and Lebel, Thierry

Subjects
*ECOHYDROLOGY, *SMALL states, *WATER table, *FLOOD risk, *WATER supply, *RUNOFF, *LUNAR craters, *WATERSHEDS
Abstract

The West African Sahel experienced a long drought from the 1970s to the 1990s during which runoff has paradoxically increased, as a response to human and climate-induced changes in surface conditions. Despite the vegetation recovery (re-greening) observed at regional scale over the past 30 years, surface runoff is still increasing, suggesting that the Sahelian eco-hydrological system passed a tipping point and is now trapped in a « high runoff » state. To study this hypothesis, we developed a system dynamics model incorporating vegetation-hydrology interactions at annual time scale. The model successfully reproduced the vegetation collapse and the increase of runoff-prone bare soil areas monitored over 65 years on a pilot site in Northern Mali. Our results confirmed the existence of a tipping point between alternative high/low runoff states at the small catchment scale. According to the model, a reverse shift to the pre-drought low runoff state is possible, but the conditions in which this shift would occur remain uncertain. The system trajectory presents a strong sensitivity to annual rainfall variability (amplitude and temporal structure). This study suggests that the increasing runoff in a re-greening environment is caused by the tipping of some areas to a high runoff/low vegetation state, illustrating how a regime shift in sub-systems can result in eco-hydrological changes at larger scale. The associated large-scale changes of the rainfall partitioning may alter evapo-transpiration and thus the surface-atmosphere feed-back. Those changes also bear strong environmental and socio-economic consequences, either adverse (increase of degraded areas to the detriment of agriculture, and increased flood risk) or beneficial (increased water resource in ponds and water tables). [ABSTRACT FROM AUTHOR]

Published
2019

9. Einheit zur messung der sedimentationsgeschwindigkeit von partikeln in suspension in einem fluid und vorrichtung mit mindestens einer derartigen einheit und einem automatischen probennehmer

Author

Nicolas Gratiot, Bernard Mercier, Cédric Legout, Valentin Wendling, Catherine Coulaud, Hanri Mora, Wendling, Valentin, and Jeunes Chercheuses et Jeunes Chercheurs - Système de caractérisation des agrégats et des flocs dans les cours d'eau et rivières chargées - - SCAF2012 - ANR-12-JS06-0006 - JC - VALID

Subjects
[SDE] Environmental Sciences, [SPI] Engineering Sciences [physics], [SDU.STU.HY] Sciences of the Universe [physics]/Earth Sciences/Hydrology, [PHYS.MECA.MEFL] Physics [physics]/Mechanics [physics]/Fluid mechanics [physics.class-ph]
Abstract

A unit for measuring the falling speed of particles in suspension in a fluid comprises a sealed container (6) having an opening (9) and defining an open compartment (15) comprising the opening and intended to contain the fluid, and a sealed compartment (16), sealing means separating the open compartment from the sealed compartment, and means for measuring the falling speed placed in the sealed compartment and comprising at least three electromagnetic radiation emitters distributed along a longitudinal axis (L) of the open compartment, each emitter being oriented according to a radiation axis crossing the open compartment at different heights along the longitudinal axis, an equal number of receivers distributed along the longitudinal axis, each receiver being placed in the radiation axis of a corresponding emitter, means for controlling the emitters and the receivers, and a system for acquiring data connected to the receivers, the acquired data being used to obtain the falling speed of the particles and the change of same as a function of the height in the open compartment and as a function of time, said change quantifying the flocculation of the particles.

Published
2015

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