La méthode Inondabilité : appropriation par les hydrologues de la vulnérabilité dans le diagnostic sur le risque d'inondation

Direction d'ouvrage : Sylvia Becerra et Anne PeltierLa méthode Inondabilité a été développée dans les années 1990 par le Cemagref pour disposer d'un outil d'évaluation du risque d'inondation à l'échelle du bassin versant et proposer un cadre de négociation sur la notion de risque acceptable. Elle repose sur l'idée d'exprimer aléa (intensité physique du phénomène naturel) et vulnérabilité (sensibilité d'un usage du sol aux inondations) avec une même unité hydrologique, la période de retour. Pour l'aléa, il s'agit de la période de retour de la première crue inondante. Pour la vulnérabilité, l'usager indique le niveau de protection souhaité en terme de période de retour, le corollaire étant qu'il accepte ou tolère d'être inondé par des crues plus importantes. Après un rappel sur les principes de la méthode Inondabilité, nous présentons une discussion sur la définition hydrologique de la vulnérabilité, et un travail complémentaire effectué sur l'évaluation économique du consentement à payer pour bénéficier de mesures de protection contre les inondations. / The Inondabilite method has been developed in the nineties by Cemagref as a tool for flood risk assessment at a basin scale. The main idea was to propose a framework of negotiation on acceptable flood risk. Both components, flood hazard and flood vulnerabilty were defined as a return period, the former being related to the first overflowing event, the latter being related to the expected level of protection. After a presentation on the Inondabilite framework, a discussion gives the advantages and limitations of such hydrological assessment of flood vulnerability. A complementary work is presented on the economical assessment of the willingness of population to pay for flood risk mitigation

La méthode Inondabilité : appropriation par les hydrologues de la vulnérabilité dans le diagnostic sur le risque d'inondation

La méthode Inondabilité a été développée dans les années 1990 par le Cemagref pour disposer d'un outil d'évaluation du risque d'inondation à l'échelle du bassin versant et proposer un cadre de négociation sur la notion de risque acceptable. Elle repose sur l'idée d'exprimer aléa (intensité physique du phénomène naturel) et vulnérabilité (sensibilité d'un usage du sol aux inondations) avec une même unité hydrologique, la période de retour. Pour l'aléa, il s'agit de la période de retour de la première crue inondante. Pour la vulnérabilité, l'usager indique le niveau de protection souhaité en terme de période de retour, le corollaire étant qu'il accepte ou tolère d'être inondé par des crues plus importantes. Après un rappel sur les principes de la méthode Inondabilité, nous présentons une discussion sur la définition hydrologique de la vulnérabilité, et un travail complémentaire effectué sur l'évaluation économique du consentement à payer pour bénéficier de mesures de protection contre les inondations. / The Inondabilite method has been developed in the nineties by Cemagref as a tool for flood risk assessment at a basin scale. The main idea was to propose a framework of negotiation on acceptable flood risk. Both components, flood hazard and flood vulnerabilty were defined as a return period, the former being related to the first overflowing event, the latter being related to the expected level of protection. After a presentation on the Inondabilite framework, a discussion gives the advantages and limitations of such hydrological assessment of flood vulnerability. A complementary work is presented on the economical assessment of the willingness of population to pay for flood risk mitigation.Inondabilité; Vulnerabilité; Crue; Evaluation des risques; Economie; Aléa; Consentement à payer

Review Article: "Flood damage assessment on agricultural areas: review and analysis of existing methods"

In Europe, economic evaluation of flood management projects is becoming a commonly used decision tool. At the same time, flood management policies shift towards new concepts such as giving more room to water by restoring floodplain and living with floods. Agricultural areas are particularly targeted by these policies since they are more frequently located in floodplain areas and are considered less vulnerable than other assets such as cities or industries. Since additional or avoided damage on agriculture may have a high influence on the efficiency of these policies, flood damage assessment on agricultural areas becomes an issue to tackle. This paper reviews existing studies addressing the question of flood damage on agriculture. Based on 41 studies, which can be qualitative or quantitative approaches, we propose a conceptual framework to analyze evaluation methods. Then, 26 studies which propose a method to evaluate agricultural damage are analyzed according to the following criterias: types of damage considered, influencing flood parameters chosen and monetized damage indicators used. The main findings of this review are that existing methods focus mainly on crop damage and do not allow correct evaluation of new flood management policies. Finally, future research challenges and recommendations for practitioners are highlighted

Risk-sharing policies in the context of the French Flood Prevention Action Programmes

This article analyzes the consequences for risk distribution of the French Flood Prevention Action Programme (PAPI). By redirecting floods from the most vulnerable to the least vulnerable areas, PAPIs expose farmers to greater flood risks. This has led local water management institutions to introduce compensation payments. The article outlines the results of an exhaustive survey of all PAPI programmes in France, which examined the way the compensation policies are set up locally. Results of the survey showed that the proposed policies may be financially non-viable. Several more viable risk-sharing solutions are then discussed, involving insurance schemes, state intervention and local institutions.flood risk management; flood storage; washland creation; risk transfer; compensation payments; insurance; floodplain restoration; over-flooding; damage assessment.

Résilience et fabrique territoriale des risques. Perspectives croisées à partir de trois programmes de recherche

International audienceAs environmental and climate issues face the question of risks, new paradigms flourish in the field of flood management: preparation, vulnerability, sustainable development, adaptation and today resilience. The ongoing urbanisation and development of places at risk create huge controversies. The concept of resilience does not seem to solve conflicts between land uses and rules, between prevention and development, between national and local regulation. If the concept is a success in the academic field, resilience does not provide the expected answers, and it even seems to raise new ambiguities. The paper shows the problems and opportunities of the implementation of the concept of resilience at local level. It aims to take it as a mean to analyse the evolution of developing spaces in France nowadays. Based on the first results from three research projects, we will present several French case studies showing what they teach us about the transformation of temporality, action, democracy and justice.À mesure que les perspectives environnementales et climatiques viennent percuter la question des risques d’inondation, de nouvelles notions s’ajoutent aux concepts pour prévenir et gérer les risques : préparation, vulnérabilité, développement durable, adaptation puis, aujourd’hui, résilience. La poursuite du développement territorial face à l’exposition aux risques pose toujours question, voire suscite des tensions sur les territoires. La notion de résilience ne semble pas résoudre les contradictions territoriales entre usage et règle, développement et prévention, national et local. Si le concept fait fureur, la résilience n’offre pas les réponses escomptées, peut-être même soulève-t-elle de nouvelles ambiguïtés. La communication montre en quoi les écueils et les opportunités que projettent les tentatives d’inscription d’une forme de résilience sur nos terrains d’étude et comment ils permettent de comprendre les enjeux des territoires en développement. Sur la base des premiers résultats produits par trois projets de recherche en cours, nous présenterons plusieurs terrains de recherche français en montrant comment ils interrogent la transformation de la temporalité, de l’action, de la démocratie et de la justice

Latin Hypercube Sampling of Gaussian random field for Sobol' global sensitivity analysis of models with spatial inputs and scalar output

4 pagesInternational audienceThe variance-based Sobol' approach is one of the few global sensitivity analysis methods that is suitable for complex models with spatially distributed inputs. Yet it needs a large number of model runs to compute sensitivity indices: in the case of models where some inputs are 2D Gaussian random fields, it is of great importance to generate a relatively small set of map realizations capturing most of the variability of the spatial inputs. The purpose of this paper is to discuss the use of Latin Hypercube Sampling (LHS) of geostatistical simulations to reach better efficiency in the computation of Sobol' sensitivity indices on spatial models. Sensitivity indices are estimated on a simple analytical model with a spatial input, for increasing sample size, using either Simple Random Sampling (SRS) or LHS to generate input map realizations. Results show that using LHS rather than SRS yields sensitivity indices estimates which are slightly more precise (smaller variance), with no significant improvement of bias

Sensitivity analysis of spatial models using geostatistical simulation

International audienceGeostatistical simulations are used to perform a global sensitivity analysis on a model Y = f(X1 ... Xk) where one of the model inputs Xi is a continuous 2D-field. Geostatistics allow specifying uncertainty on Xi with a spatial covariance model and generating random realizations of Xi. These random realizations are used to propagate uncertainty through model f and estimate global sensitivity indices. Focusing on variance-based global sensitivity analysis (GSA), we assess in this paper how sensitivity indices vary with covariance parameters (range, sill, nugget). Results give a better understanding on how and when to use geostatistical simulations for sensitivity analysis of spatially distributed models

Analyse de sensibilité globale d'un modèle d'évaluation économique du risque d'inondation

International audienceVariance-based Sobol' global sensitivity analysis (GSA) was initially designed for the study of models with scalar inputs and outputs, while many models in the environmental eld are spatially explicit. As a result, GSA is not a common practise in environmental modelling. In this paper we describe a detailed case study where GSA is performed on a spatially dependent model for flood risk economic assessment on the Orb valley (southeast France). The realisations of random input maps can be generated by any method including geostatistical simulation techniques, allowing for spatial structure and auto-correlation to be taken into account. The estimation of sensitivity indices on ACB-DE spatial outputs makes it possible to produce maps of sensitivity indices. These maps describe the spatial variability of Sobol' indices. Sensitivity maps of di fferent resolutions are then compared to discuss the relative influence of uncertain input factors at diff erent scales

Ranking sources of uncertainty in flood damage modelling: a case study on the cost-benefit analysis of a flood mitigation project in the Orb Delta, France

International audienceCost-benefit analyses (CBA) of flood management plans usually require estimating expected annual flood damages on a study area, and rely on a complex modelling chain including hydrological, hydraulic and economic modelling as well as GIS-based spatial analysis. As most model-based assessments, these CBA are fraught with uncertainty. In this paper, we consider as a case-study the CBA of a set of flood control structural measures on the Orb Delta, France. We demonstrate the use of variance-based global sensitivity analysis (VB-GSA) to i) propagate uncertainty sources through the modelling chain and assess their overall impact on the outcomes of the CBA, and ii) rank uncertainty sources according to their contribution to the variance of the CBA outcomes. All uncertainty sources prove to explain a significant share of the overall output variance. Results show that the ranking of uncertainty sources depends not only on the economic sector considered (private housing, agricultural land, other economic activities), but also on a number of averaging-out effects controlled by the number and surface area of the assets considered, the number of land use types or the number of damage functions

Erlang-based dimensioning for IPv4 Address+Port translation

International audienceAs the IPv4 address pool is being exhausted, it becomes urgent to find a way to migrate IPv4 network architectures to IPv6, or to reduce the use of IPv4 addresses. In this paper, we discuss a strategy known as ''Address + Port'' translation, which consists in several users sharing the same IPv4 address and being distinguished by a range of port numbers. Of critical importance for the feasibility of such a mechanism is the knowledge of the minimum number of ports to allocate to users so that no service degradation is perceived. To that extent, we analyse the port consumption of the most port-consuming Internet applications, web browsing, and present some aggregate port consumption curves for the student population of our campus. Our results suggest that a port range of 1000 ports is totally transparent to users (which would allow to share a single IPv4 address among 64 users),while 400 ports (i.e., 150 users per address) is sufficient for most of users. Finally, the number of users per address could be further improved by benefiting from statistical multiplexing, i.e., using dynamical instead of fixed port range allocation