Impacts de le récupération des eaux pluviales sur le régime hydrologique de petits bassins versants partiellement urbanisés

International audienceRainwater harvesting is a relevant and sustainable solution to reduce the pressure on conventional water resources. Rainwater harvesting techniques can as well provide stormwater management benefits through the reduction of runoff volumes. The impact of a wide implementation of these practices on the hydrological regimes of already disturbed catchments however remains unclear. The capture of significant fraction of runoff volume in urbanized areas to satisfy various uses, could in particular result in an over-extraction of water, exacerbating low streamflow issues. In this study, a method associating geodata processing and allotment-scale hydrological modeling is introduced to investigate the impact of rainwater harvesting on the hydrology of two semi-urban catchments, addressing both stormwater management benefits and low-flow effects. Results indicate that rainwater harvesting alone is unlikely to meet usual runoff-control objectives, but as well suggest that a systematic implementation of these practices on upstream catchments that already face low water flow issues might be detrimental to stream health.La récupération des eaux de pluie suscite aujourd'hui un intérêt croissant du fait des incertitudes sur la disponibilité future des ressources en eau. Celle-ci est par ailleurs fréquemment envisagée comme un moyen de limiter à la source les volumes de ruissellement générés niveau des surfaces revêtues, participant ainsi à la gestion des eaux pluviales urbaines. La perspective d'une mise en oeuvre de politiques incitatives de récupération des eaux pluviales impose cependant de s'interroger sur l'incidence de cette pratique sur le régime hydrologique de certains bassins versants. Dans les secteurs urbanisés, pour lesquels le potentiel de développement de la récupération des eaux pluviales est important, l'interception d'une fraction significative du ruissellement pour satisfaire divers usages pourrait en effet conduire à un déséquilibre hydrologique se traduisant par une aggravation des étiages. Une méthode associant modélisation hydrologique et exploitation de données géographiques est ici introduite pour construire différents scénarios de récupération des eaux pluviales et évaluer leur incidence de sur le régime hydrologique deux bassins-versants semi-urbains. L'analyse suggère ici que cette pratique n'est à elle seule pas suffisante pour satisfaire les objectifs usuels de gestion des eaux pluviales mais indique que sa systématisation sur des têtes de bassins versant présentant de faibles débits pourrait en revanche donner lieu à une aggravation des étiage

Use of green roofs to solve storm water issues at the basin scale – Study in the Hauts-de-Seine County (France)

International audienceAt the building scale, green roof has demonstrated a positive impact on urban runoff (decrease in the peak discharge and runoff volume). This work aims to study if similar impacts can be observed at basin scale. It is particularly focused on the possibility to solve some operational issues caused by storm water.For this purpose, a methodology has been proposed. It combines: a method to estimate the maximum roof area that can be covered by green roof, called green roofing potential, and an urban rainfall-runoff model able to simulate the hydrological behaviour of green roof.This methodology was applied to two urban catchments affected one by flooding and the other one by combined sewage overflow. The results show that green roof can reduce the frequency and the magnitude of such problems depending on the covered roof surface. Combined with other infrastructures, they represent an interesting solution for urban water management

Elevation Changes Inferred From TanDEM-X Data Over the Mont-Blanc Area: Impact of the X-Band Interferometric Bias

International audienceThe TanDEM-X mission allows generation of Digital Elevation Models (DEM) with high potential for glacier monitoring, but the radar penetration into snow and ice remains a main source of uncertainty. In this study, we generate 5 new DEMs of the Mont-Blanc area from [...

Suivi du fonctionnement d’une toiture végétalisée stockante

International audienc

Nucleation of Al3Zr and Al3Sc in aluminum alloys: from kinetic Monte Carlo simulations to classical theory

Zr and Sc precipitate in aluminum alloys to form the compounds Al3Zr and Al3Sc which for low supersaturations of the solid solution have the L12 structure. The aim of the present study is to model at an atomic scale this kinetics of precipitation and to build a mesoscopic model based on classical nucleation theory so as to extend the field of supersaturations and annealing times that can be simulated. We use some ab-initio calculations and experimental data to fit an Ising model describing thermodynamics of the Al-Zr and Al-Sc systems. Kinetic behavior is described by means of an atom-vacancy exchange mechanism. This allows us to simulate with a kinetic Monte Carlo algorithm kinetics of precipitation of Al3Zr and Al3Sc. These kinetics are then used to test the classical nucleation theory. In this purpose, we deduce from our atomic model an isotropic interface free energy which is consistent with the one deduced from experimental kinetics and a nucleation free energy. We test di erent mean-field approximations (Bragg-Williams approximation as well as Cluster Variation Method) for these parameters. The classical nucleation theory is coherent with the kinetic Monte Carlo simulations only when CVM is used: it manages to reproduce the cluster size distribution in the metastable solid solution and its evolution as well as the steady-state nucleation rate. We also find that the capillary approximation used in the classical nucleation theory works surprisingly well when compared to a direct calculation of the free energy of formation for small L12 clusters.Comment: submitted to Physical Review B (2004

Retour d'expériences national sur les bassins d'orage en réseau unitaire

International audienc

Retour d'expérience sur les bassins d'orage en réseau unitaire: une solution pour limiter les rejets de temps de pluie

International audienceLe développement des systèmes d'assainissement s'appuie souvent sur des structures construites il y a plusieurs décennies. Ces systèmes font face à une augmentation des niveaux d'exigence qui leur sont assignés. Dans le viseur de l'arrêté de 2015 notamment, les performances par temps de pluie des systèmes de collecte. Un retour d'expériences sur les bassins d'orage mené par le Cerema fait le point sur les interrogations et les solutions trouvées par les gestionnaires. CONTEXTE DE L'ETUDE En collaboration avec l'AFB, le GEMCEA, le Ministère de la transition écologique et solidaire et les Agences de l'eau, le Cerema a réalisé un vaste retour d'expériences sur les bassins d'orage implantés sur les réseaux d'assainissement unitaires. L'objet de ce retour d'expériences était de voir, sur le terrain, comment les gestionnaires/exploitants avaient eu recours à cette technique pour optimiser le fonctionnement de leur système, notamment par temps de pluie, et de collecter des informations techniques et financières quant au fonctionnement, à la conception, au dimensionnement de ce type d'ouvrages. A travers une recherche bibliographique et de nombreux entretiens réalisés auprès de 17 maîtres d'ouvrage/exploitants, ce travail a aussi permis indirectement de recueillir les témoignages des personnes interrogées quant aux enjeux et aux problématiques auxquelles les services peuvent être confrontés, aux difficultés techniques rencontrées, souvent liées à leur contexte local, et à la façon dont les collectivités ont cherché à y remédier notamment par la construction de bassins d'orage. Le projet ayant débuté au 2nd semestre 2013 et s'étant terminé en 2018, nous avons ainsi pu être les témoins, un peu malgré nous, des interrogations des différents acteurs vis-à-vis des évolutions de la réglementation en matière d'assainissement : autosurveillance, diagnostic permanent, choix du critère de conformité du système de collecte, … ainsi que des conséquences des lois NOTRe 5 et MAPTAM 6 sur la répartition des compétences à court et moyen termes. Cette communication fait volontairement le choix de se focaliser sur les éléments recueillis qui concernent les enjeux et opportunités de l'autosurveillance et du diagnostic permanent, les démarches mises en place par les gestionnaires pour optimiser le fonctionnement de leur système et répondre aux nouveaux critères de conformité fixés par l'arrêté de 2015

Evolutionary algorithms converge towards evolved biological photonic structures

Nature features a plethora of extraordinary photonic architectures that have been optimized through natural evolution in order to more efciently refect, absorb or scatter light. While numerical optimization is increasingly and successfully used in photonics, it has yet to replicate any of these complex naturally occurring structures. Using evolutionary algorithms inspired by natural evolution and performing particular optimizations (maximize refection for a given wavelength, for a broad range of wavelength or maximize the scattering of light), we have retrieved the most stereotypical natural photonic structures. Whether those structures are Bragg mirrors, chirped dielectric mirrors or the gratings on top of Morpho butterfy wings, our results indicate how such regular structures might have spontaneously emerged in nature and to which precise optical or fabrication constraints they respond. Comparing algorithms show that recombination between individuals, inspired by sexual reproduction, confers a clear advantage that can be linked to the fact that photonic structures are fundamentally modular: each part of the structure has a role which can be understood almost independently from the rest. Such an in silico evolution also suggests original and elegant solutions to practical problems, as illustrated by the design of counter-intuitive anti-refective coatings for solar cells

Brain Health Services: organization, structure, and challenges for implementation. A user manual for Brain Health Services—part 1 of 6

Dementia has a devastating impact on the quality of life of patients and families and comes with a huge cost to society. Dementia prevention is considered a public health priority by the World Health Organization. Delaying the onset of dementia by treating associated risk factors will bring huge individual and societal benefit. Empirical evidence suggests that, in higher-income countries, dementia incidence is decreasing as a result of healthier lifestyles. This observation supports the notion that preventing dementia is possible and that a certain degree of prevention is already in action. Further reduction of dementia incidence through deliberate prevention plans is needed to counteract its growing prevalence due to increasing life expectancy. An increasing number of individuals with normal cognitive performance seek help in the current memory clinics asking an evaluation of their dementia risk, preventive interventions, or interventions to ameliorate their cognitive performance. Consistent evidence suggests that some of these individuals are indeed at increased risk of dementia. This new health demand asks for a shift of target population, from patients with cognitive impairment to worried but cognitively unimpaired individuals. However, current memory clinics do not have the programs and protocols in place to deal with this new population. We envision the development of new services, henceforth called Brain Health Services, devoted to respond to demands from cognitively unimpaired individuals concerned about their risk of dementia. The missions of Brain Health Services will be (i) dementia risk profiling, (ii) dementia risk communication, (iii) dementia risk reduction, and (iv) cognitive enhancement. In this paper, we present the organizational and structural challenges associated with the set-up of Brain Health Services