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Search Results: 1 - 10 of 1272 matches for " Florence Naaim-Bouvet "
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Risques naturels en montagne : Avant-propos
Florence Naaim-Bouvet
Sciences Eaux & Territoires : la Revue du IRSTEA , 2010,
Abstract: Confrontées aux risques naturels, les communes de montagne doivent concilier une demande croissante de sécurisation et des exigences de développement économique impliquant l’extension spatiale des enjeux exposés. La demande d’expertise de la part des collectivités mais également d’appui aux politiques publiques est croissante et de plus en plus pointue. C’est dans ce contexte que se situe l’activité de l’unité de recherche érosion torrentielle, neige et avalanche (UR ETNA) du Cemagref.Voir le sommaire du numéro
Glossaire et index des sigles
Florence Naaim-Bouvet
Sciences Eaux & Territoires : la Revue du IRSTEA , 2010,
Abstract: Glossaire et index des sigles.
Les capteurs de transport de neige par le vent au banc d'essai Intercomparaison between drifting snow sensors
Hervé Bellot et Florence Naaim-Bouvet
Sciences Eaux & Territoires : la Revue du IRSTEA , 2010,
Abstract: Le transport de la neige par le vent entra ne la formation de congères, augmente le risque d'avalanches et limite la visibilité. Afin d’améliorer la prévision du phénomène et de développer une ingénierie de protection, les acteurs locaux de la prévention ont besoin d’informations précises sur les quantités de neige transportée par le vent. Cet article fait le point sur les différentes technologies de mesure disponibles en comparant des essais réalisés in situ et en soufflerie avec plusieurs types de capteurs. Wind-transported snow is a common phenomenon in cold windy areas such as mountainous and polar regions. The resulting snowdrifts often cause problems for infrastructure and road maintenance and contribute significantly to the loading of the avalanche release area. It also reduces visibility. It is very important to better determine drifting snow fluxes in the framework of forecast or mitigation. Therefore this article reviews the different available technologies such as mechanical traps, acoustic or optical sensors. It bases its conclusion on essays carried out in wind-tunnel and on in situ experimental site at Col du Lac Blanc which is dedicated to the study of drifting snow. If acoustic sensors are not so promising as expected, optical sensors give accurate results. Nevertheless the measurement area is small-sized. That is why the coupling with a theoretical approach is still indispensable.
Focus : Dispositif expérimentaux pare-congères du Puy-de-D me
Florence Naaim-Bouvet, Sylvie Monier et Sylvie Ougier
Sciences Eaux & Territoires : la Revue du IRSTEA , 2010,
Abstract: Le conseil général du Puy-de-D me est confronté chaque année à la formation de congères, impliquant des dépenses conséquentes pour assurer la viabilité de ses routes départementales. Afin de trouver des solutions pérennes dans le temps, une étude expérimentale de plantation de haies pour lutter contre la formation de congères a été réalisée sur quatre sites expérimentaux.
Focus : Bande boisée du Col de La Fageole
Florence Naaim-Bouvet, Sylvie Monier et Sylvie Ougier
Sciences Eaux & Territoires : la Revue du IRSTEA , 2010,
Abstract: Au Col de la Fageole, une bande boisée a été mise en place il y a vingt ans pour protéger la route nationale contre la formation de congères. Qu'en-est-il aujourd'hui ?
Haies et boisements pare-congères : de la théorie à la pratique Hedges and afforestration to prevent damage from blowing snow: from theory to practice
Florence Naaim-Bouvet, Sylvie Monier et Sylvie Ougier
Sciences Eaux & Territoires : la Revue du IRSTEA , 2010,
Abstract: Lorsque la neige et le vent s'associent, ils créent des congères qui vont gêner la circulation sur les routes et les chemins de montagne. Pour lutter contre ce problème, l'implantation de haies et de boisements apparait comme une solution écologique et durable. Quels sont les principes de fonctionnement ? Où et comment implanter ces haies pour constituer un barrage efficace à la neige ? Quelles essences choisir et quel entretien cela suppose-t-il ? Cet article fait le point sur les connaissances disponibles afin de répondre aux préoccupations des gestionnaires. Blowing and drifting snow can generate snowdrifts on roads and railways. This is an important issue for instance in the Massif Central (France) where limited snowfalls on vast areas can locally lead to huge snow accumulations. This problem is not new and prevention measures were designed and tested as early as the end of the 19th century. However, the development of efficient snow clearing vehicles in the second half of the 20th century led to some decrease of research efforts (mostly a trial and error approach) on traditional prevention measures such as afforestration and hedges. Nevertheless, the renewed interest in ecological engineering, dating from the early 90s has yielded to new research efforts on that topic, even though such measures are not effective on short term. Currently, bioengineering tallies meet the requirements of sustainable development and of long term management, accordingly. In this context, this paper aims at giving a new vision of hedges and afforestration, taken as protection measures against snowdrifting, through the eyes of a fluid mechanics researcher, a forest engineer and a territories manager. The principles of action, setting and species choice are presented through case studies with emphasis on difficulties related to land property and long and short-term maintenance.
La modélisation au service de la conception des ouvrages de protection : étude du site avalancheux de Taconnaz
Mohamed Naaim, Thierry Faug, Florence Naaim-Bouvet et Nicolas Eckert
Sciences Eaux & Territoires : la Revue du IRSTEA , 2010,
Abstract: Optimiser la conception des ouvrages de protection contre les avalanches est une priorité pour la sécurité en montagne. à partir d'une étude réalisée dans le cadre des travaux de renforcement de l'ouvrage paravalanche du glacier de Taconnaz, construit voilà vingt ans et montrant aujourd'hui ses limites, les auteurs nous démontrent ici comment une méthode combinant données historiques, statistique et modélisation peut être utilisée pour améliorer un dispositif paravalanche.
Snow fences on slopes at high wind speed: physical modelling in the CSTB cold wind tunnel
F. Naaim-Bouvet,M. Naaim,J.-L. Michaux
Natural Hazards and Earth System Sciences (NHESS) & Discussions (NHESSD) , 2002,
Abstract: In order to determine the effect of steep slopes on snowdrift generated by snow fences, we have conducted physical modeling experiments in the CSTB (Centre Scientifique et Technique du Batiment) cold wind tunnel as part of the European project "Access to Large Facilities". After an overview of previous studies and an accurate description of the drifting snow process inside the experimental chamber, we present the main results obtained. (1) On flat areas, even for high wind speed, the acknowledged results for moderate wind are still valid: the porous snow fence (50%) is the most efficacious and the bottom gap increases the efficacy of the dense snow fence. (2) The steeper the slope is, the less effective all tested snow fences are. Their effectiveness decreases considerably: the snow catch is approximately divided by two for a slope of 10°. (3) Contrary to flat areas, on steep slopes, the "efficacy" is greater for a dense snow fence.
Physical modelling of the interaction between powder avalanches and defence structures
F. Naaim-Bouvet,M. Naaim,M. Bacher,L. Heiligenstein
Natural Hazards and Earth System Sciences (NHESS) & Discussions (NHESSD) , 2002,
Abstract: In order to better understand the interaction between powder snow avalanches and defence structures, we carried out physical experiments on small-scale models. The powder snow avalanche was simulated by a heavy salt solution in a water tank. Quasi two-dimensional and three-dimensional experiments were carried out with different catching dam heights. For the reference avalanche, the velocity just behind the nose in the head was greater than the front velocity. For the 2-D configuration, the ratio Umax/Ufront was as high as 1.6, but it depends on the height. For the 3-D configuration, this ratio differed slightly and was even greater (up to 1.8). The vertical velocity rose to 106% of the front velocity for the 3-D simulation and 74% for the 2-D simulation. The reduction in front velocity due to the presence of dams was an increasing function of the dam height. But this reduction depended on topography: dams were more effective on an open slope avalanche (3-D configuration). The ratio Umax/Ufront was an increasing function of the dam’s height and reached a value of 1.9. The obstacle led to a reduction in vertical velocity downstream of the vortex zone.
Effect of unsteady wind on drifting snow: first investigations
J.-L. Michaux,F. Naaim-Bouvet,M. Naaim,M. Lehning
Natural Hazards and Earth System Sciences (NHESS) & Discussions (NHESSD) , 2002,
Abstract: Wind is not always a steady flow. It can oscillate, producing blasts. However, most of the current numerical models of drifting snow are constrained by one major assumption: forcing winds are steady and uniform. Moreover, very few studies have been done to verify this hypothesis, because of the lack of available instrumentation and measurement difficulties. Therefore, too little is known about the possible role of wind gust in drifting snow. In order to better understand the effect of unsteady winds, we have performed both experiments at the climatic wind tunnel at the CSTB (Centre Scientifique et Technique des Batiments) in Nantes, France, and in situ experiments on our experimental high-altitude site, at the Lac Blanc Pass. These experiments were carried out collaboratively with Cemagref (France), Météo-France, and the IFENA (Switzerland). Through the wind tunnel experiments, we found that drifting snow is in a state of permanent disequilibrium in the presence of fluctuating airflows. In addition, the in situ experiments show that the largest drifting snow episodes appear during periods of roughly constant strong wind, whereas a short but strong blast does not produce significant drifting snow. Key words. Drifting snow, blowing snow, gust, blast, acoustic sensor
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