Une aide à la décision pour le choix des interventions en zone inondable

Cet article a été réalisé dans le cadre d'un projet de trois ans visant à développer une méthodologie d'analyse, de prévision et de contrôle des risques d'inondation au Québec. Il présente une approche concrète pour calculer les impacts potentiels et le risque d'inondation et utiliser ces résultats afin d'évaluer la situation du risque local, de décider si les impacts doivent être minimisés et de choisir les moyens d'intervention appropriés. Le risque d'inondation est considéré comme étant le produit de la probabilité d'occurrence des crues et des conséquences occasionnées par ces événements. Les pertes de vies potentielles et les dommages directs sont évalués en simulant les niveaux d'eau de différents scénarios d'inondation à partir d'un modèle d'écoulement unidimensionnel non permanent, et en intégrant ces résultats à un logiciel géoréférencé de calcul des dommages d'inondation. L'analyse des impacts et du risque calculé permet de dresser un portrait du montant des dommages annuels potentiels sur les sites habités le long du cours d'eau et un portrait de l'évolution des impacts en fonction de l'amplitude des crues. Cette analyse mène à l'identification des sites où existe un risque jugé inacceptable selon des critères préétablis. Pour chaque site où des interventions sont justifiées par le niveau de risque, des scénarios de minimisation des impacts tenant compte des mécanismes d'inondation sont élaborés et ensuite simulés afin d'en mesurer l'efficacité. Un exemple d'application à un site de la rivière Châteauguay illustre la méthode et les gains pouvant découler de son utilisation.Each year, several rivers in Quebec are responsible for severe flooding and these events generate major socio-economic impacts. The frequency and magnitude of these episodes highlight the existence of a real flood risk. Using global information concerning level and extent of flood risk, authorities would be more likely to make appropriate decisions in the management of flood risk. This article results from a three year project aimed at developing a methodology for the analysis, forecasting and control of flood risk in Quebec. It suggests a concrete approach for the evaluation of the potential impact of floods in order to obtain a better knowledge of local risk in inhabited areas and exploits there results to evaluate the acceptability of the calculated risk and to plan appropriate risk minimisation interventions.Risk is defined as the product of the mathematical expectation of a specified occurrence with the expected consequences of the event. In floodplain studies, flood risk is the probability of the occurrence at a given flood multiplied by the expected consequences resulting from this event. Different types of consequences may be observed, clearly the easiest to evaluate being direct or material damages and potential loss of life. The risk calculated using the proposed definition is attributable in variable proportions to the frequency of the floods and the amount of damages. A given calculated global risk on a site could be the result of frequent floods, each causing moderate damage or of a single (or more) extreme event, with very low probability of occurrence, but causing severe damage. Risk associated with rare events could be considered as an acceptable risk, a risk we decide to live with, since the resources available to prevent flood damage are often limited and a decision is taken to optimise the allocation of these resources. The flood level corresponding to the limit between acceptable and unacceptable risk must be determined by the population concerned and be based on a good knowledge of the risk situation.The proposed methodology to evaluate and minimise flood risk for a site localised in a river flood plain involves six steps:1. the realisation of a hydrologic frequency analysis to determine the amplitude of the floods associated with the flood frequency,2. the hydraulic simulation of floods to predict water level and velocity in the stream for each scenario, 3. the assessment of direct damage and potential loss of life for each flood simulated, 4. the calculation of risk, 5. the risk analysis considering the limit of acceptable risk and 6. the choice and planning of appropriate intervention to eliminate unacceptable risk.This approach has been applied to the study of a site along the Châteauguay River, a tributary of the St Laurence River, a river that experiences flood events every two years or so. Seven flood scenarios (the 2, 3, 10, 20, 100, 1 000, and 10 000 year flood) are used to evaluate the risk for a site localised in the village of Huntingdon. Hydraulic characteristics, water level and velocity, associated with each flood scenario are determined using the DAMBRK model, a one-dimensional unsteady flow model. The results are incorporated in DOMINO, a geo-referenced software calculating flood impacts. This software allows the user to create a three-dimensional numerical model of the site based on topographic information. The superposition of hydraulic results provides the flow depth at any point within the site. Damage is evaluated by integrating the municipal roll number of Huntingdon, which provide the site location and value of each building, and gives an estimate of the population threatened by each flood event at the site. These results of direct damages are used to calculate the risk related to each flood event simulated on the Huntingdon site. For this application, the unacceptable risk has generally been agreed to be the risk resulting from the 20 year flood, or more frequent floods, for the material damages and to the number of potential losses of life associated with the 100 year flood or more frequent flood. The analysis indicates that an unacceptable risk of 23 993 $ per year for material damages and potential loss of life of 50 persons exist. Different site scale interventions to eliminate this risk have been simulated and proven to be efficient only if complemented with a few local modifications to the more exposed buildings.This approach may be extended to the study of any river because it takes into consideration local hydrologic and hydraulic conditions. It has the advantage of being based on existing information and to be automated, which limits the time and resources required to obtain the base data and perform the necessary simulations

Une contribution expérimentale à l'étude de l'érosion d'une digue par submersion et son analyse

Dans cet article, on décrit un essai réalisé sous conditions contrôlées en laboratoire concernant l'initiation et le démarrage de la rupture par submersion d'une digue de revanche homogène et en moraine, un matériel utilisé dans les ouvrages réels, de granulométrie étendue et sans cohésion.Les résultats obtenus sur cette digue expérimentale ont montré que le mécanisme de formation et d'érosion de brèche est très différent du mécanisme global et moyen de développement et de progression de la brèche adopté dans les modèles courants de calcul des ruptures de barrages. L'essai souligne l'importance de la turbulence et des pertes de charge locales dans certaines zones spécifiques de l'écoulement et met en évidence le rôle de l'instabilité des parois latérales de la brèche dont la base est sapée continuellement.L'essai a été stoppé à un moment précis, soit lorsque l'accroissement rapide du débit de rupture était confirmé, afin de préserver les caractéristiques géométriques précises de la brèche en cours de formation. Les données ainsi recueillies sur la rupture de la digue d'essai sont utiles à tout développeur voulant valider sa compréhension physique de l'érosion de brèche ou un outil de calcul visant à reproduire ce mécanisme. Le texte présente aussi une analyse comparative effectuée par un outil informatique de prévision, BRECHE, et la confrontation des résultats produits selon cinq méthodes publiées durant les dernières décennies et reconnues.Une appréciation des résultats obtenus par prévision et des nombreuses données issues de l'essai réalisé sur le modèle en laboratoire est présentée et discutée.It has been recognized for several decades that the reliability of forecasts for flooding downstream from a dam failure depends not only on the local topography but also on the failure mode of the dam, specifically on the breach outflow hydrograph. It is therefore of primary importance that the mechanism of formation of the breach is anticipated with an acceptable degree of accuracy. Several approaches to model this phenomenon have been reported in the literature, but the results from these models do not appear to be reliable when the predicted values are compared with those deduced from observations carried out on real or simulated dam failures. Each failure of a dam generates a particular form of hydrograph that will have a specific impact on the affected population. The most frequent cause of failure of earthfill and rockfill dams is by overtopping of the crest, although in rockfill dams initial piping failure followed by partial collapse of the crest resulting in breach initiation has been observed. Once initiation of a breach has occurred, continuous development until complete failure occurs is virtually assured if sufficient energy from the reservoir volume is available to sustain the breaching process. For this reason, breach formation is recognized as one of the essential factors in the modeling of a dambreak.To anticipate the real hazard from dam overtopping, a predictive model for breach initiation and development would be extremely useful. Currently, the majority of dam safety studies assume a standard scenario for the breach formation, development and final failure based on some norms established as a result of regression analyses on some actual failures. Modeling of the breach and therefore prediction of the outflow hydrograph do not take into account specific local data on the construction techniques and soil properties, mainly because currently available methods that attempt to incorporate these factors still do not provide reliable results. To contribute to the understanding of the mechanism of breach formation and to determine the details of the process, a test of erosion failure was performed and documented at the Hydrodynamics Laboratory of the École Polytechnique de Montreal. This test, coupled with the subsequent development of a numerical model incorporating the interactions of the hydraulics-erosion process, has formed the basis of a doctoral dissertation, the principal objective being to reproduce as accurately as possible the mechanisms involved in the formation of a breach (ZERROUK, 2004; ZERROUK et MARCHE, 2004).This paper describes a test carried out under controlled laboratory conditions on a homogeneous dam composed of moraine, a material used in the construction of real dams with an extended non-cohesive granulometry. The test simulated the initiation and the start of the failure by dike overtopping known as a " fuse plug " i.e. a dike that, during an event of exceptional rain or extreme inflow, would be used to limit the volume retained in the reservoir. The test, carried out on a laboratory scale but extrapolated to prototype dimensions without similarity considerations, nevertheless allowed identification of the various mechanisms that intervene in the breaching process.The results obtained on this experimental dike showed that the mechanism of formation and erosion of a breach is quite different from the mechanisms assumed in standard methods of computation of the rupture. Current models give undue weight to a single failure mechanism, independent of lateral slope instability, surface erosion or shear stress energy. The laboratory test however indicated the importance of turbulence and erosion in certain specific zones of the flow and highlighted the role of sidewall instability at the base of the breach, which erodes continuously leads to lateral instability.Currently, engineers attempt to predict breach outflow based on the formation of the breach using physical properties of the component material such as the angle of friction, the slope angle of the breach channel and a factor for the rate of growth of breach width. The present authors recognize major deficiencies in this approach such as the use of assumptions for the breach geometry, the progression of the rupture, the use of material transport expressions based only on shear stress considerations (FREAD, 1984c) or the use of empirical 'adjustment' factors influencing the erosion of compacted cohesive soils (SINGH et SCARLATOS, 1989). The data acquired from the experimental dike were used in a data-processing tool for comparative analysis called BREACH, in which five methods for predicting the formation of a breach by overtopping of dams composed of granular material were programmed (ZERROUK, 2004; ZERROUK et MARCHE, 2001). Starting with the same data obtained from the laboratory test, each of the models was applied and the results discussed with respect to whether the principal factor for breach evolution that is presumed predominant for the breaching process in the model, corresponds in fact to the mechanism observed during the test.The analysis highlights the factors, ignored in the current models, which may in fact explain the mediocre results obtained for the predictions. It indicates that the characterization of the breach geometry is the major uncertainty in these models, which result in peak outflows and corresponding times never being simultaneously predicted correctly

Une méthode pour anticiper les mises en alerte de crues sur la rivière Thoré (France)

Cet article présente les conclusions d'une recherche visant l'amélioration de l'annonce des crues, et son application à la rivière Thoré, dans le contexte du système d'alerte français. On y exploite les informations météorologiques contenues couramment dans les bulletins d'alerte aux précipitations [BAP] émis par Météo-France, dans le but d'aider les prévisionnistes du Service d'annonce de crues [SAC] à anticiper l'atteinte de la cote d'alerte sur une rivière. Le travail présenté fait partie d'une approche visant à munir les SAC d'outils prévisionnels fonctionnant en temps réel et aptes à prévenir d'une mise en alerte probable. L'approche préconisée conduit à une utilisation directe des informations contenues dans les BAP reçus des services de météorologie dans le processus de surveillance des crues. C'est au moyen de courbes d'intensité-durée-temps d'alerte [IDTA], préalablement établies pour des prévisions de pluies uniformément réparties, et de courbes d'intensité-superficie-temps d'alerte [ISTA] pour les prévisions relatives à des cellules orageuses localisées, que l'approche proposée est développée.This work was designed to contribute to the improvement of flood forecasting, in the context of the French alert system. We propose that the meteorological information contained in the French weather forecast bulletin (Bulletins d'alerte aux précipitations; BAP), produced by Météo-France (French meteorological organization), should be utilized in order to aid the forecasters of the French flood forecasting agencies (Services d'annonce de crues; SAC) to anticipate the timing of an alert associated with an increase in the water level of a river. The goal was to develop an approach to provide the SAC with a real-time operational forecasting tool in order to improve the evaluation of a probable Flood Alert decision. This approach integrates the information contained in the BAP received from Météo-France into the existing flood control process with the use of Duration-Intensity-Warning Time (durée-intensité-temps d'alerte, IDTA) curves for uniform rainfall forecasting, and Intensity-Area-Warning Time curves (intensité-superficie-temps d'alerte, ISTA) for localized storm cells.The rainfall parameters considered were the intensity (I, mm/h), the duration (D, h), and the area of the watershed affected by the rainfall (S, km2). These parameters are related by the equation V=I x D x S, where V is the volume of rain (hm3). The parameter directly related to the Flood Alert decision is the warning time (Talerte), measured in hours. It is defined as the time from the beginning of the rainfall to the time when the flow at the watershed outlet reaches the alert flow (Qalerte in m3 /s), regardless of the maximum discharge (Qmax). Although Qmax may be an important indicator of the magnitude of the upcoming event, the chief concern is the Flood Alert decision, and therefore, the time to alert parameter (Talert) is of primary importance.The proposed approach involves creating a graphical connection of a series of rainfall intensity values (I) as a function of a range of rainfall (D) duration values with time to alert (Talert) curves, which represent the I-D couples. As a result, a SAC forecast agent that receives a BAP indicating the quantitative precipitation forecast in a precise region for a defined period will be able to evaluate the time after the start of the rainfall that the alert flow (Qalert) will be reached, simply by referring to the IDTA and/or ISTA curves. If an alert is foreseen within a certain delay, the flood forecast agent can wait to receive improved forecasts before making the decision whether to start the flood alert procedures or not.The construction of the IDTA and ISTA curves requires numerous simulations in order to cover a wide variety of intensity-duration and intensity-area of rainfall couples for which the alert flow (Qalert) will be reached at the watershed outlet, and therefore the time corresponding to this discharge can be estimated. The simulations were performed through the use of a combination of a deterministic distributed parameter hydrological model and a hydraulic one-dimensional hydrograph transfer model. The neuronal models of the Generalized Regression Network (GRNN) type were also used. This allowed for the extraction of and/or interpolation between values in the database containing the parameters intensity, duration, area, and the hydrographs that resulted from the simulations done with the first two models. The interest in using the GRNN model is to cover a large range of values for all of the parameters considered, without having to simulate all cases, therefore reducing the potential computation time.We developed this forecasting approach on the basis of a specific case related to the extreme flooding that occurred in southern France on November 1999. More precisely, our case study concerns the mountainous region in the upstream area of the Thoré watershed, in the Tarn Department. The simulation scenarios were 1) uniformly distributed rainfall on a watershed of 208 km2 ; 2) storm cells of 9, 36, 64 and 144 km2 located in the watershed center; and 3) a storm cell located in various zones of the watershed.The main observation of the simulation results was that the Talert was constant for a rainfall of intensity I, as long as the duration was longer than the Talert (i.e., provided it was still raining after Qalert was attained at the outlet). On the other hand, if the rain stops before Qalert is attained, Talert is delayed. Talert increases as a function of the duration of the rainfall, for a constant I. This is true for both uniform and localized rainfall.The IDTA and ISTA curves were developed on the basis of several simplifying hypotheses and should be improved in order to increase their precision and flexibility. Therefore this approach can be amended by taking into account the following factors:- infiltration (when the laws defining it are established);- the initial conditions: since the results of the simulations for this study are valid for constant initial conditions of Qini=20 m3/s, it would be pertinent to include a correction factor to adjust the results (Talert) for the real initial conditions such as the actual Qini and the actual soil humidity;- the spatial variability of the storm cells; and- the combination of uniformly distributed rainfall and localized storm cells.Nevertheless, we evaluated the use of the forecasting approach with the IDTA and ISTA curves referring to the November 1999 events. The contribution of these curves in the Flood Alert decision process was assessed with a fictitious scenario defined by the issued BAP related to this event. Understanding the simplifying hypotheses discussed above, we conclude that the flood alert on the Thoré River watershed could have been advanced up to seven hours and thirty minutes from the actual time it was issued. In a fast or flash flood event, this range of anticipation could have a considerable impact

A Cognitive Social IoT Approach for Smart Energy Management in a Real Environment

Energy usage inside buildings is a critical problem, especially considering high loads such as Heating, Ventilation and Air Conditioning (HVAC) systems: around 50% of the buildings’ energy demand resides in HVAC usage which causes a significant waste of energy resources due to improper uses. Usage awareness and efficient management have the potential to reduce related costs. However, strict saving policies may contrast with users’ comfort. In this sense, this paper proposes a multi-user multi-room smart energy management approach where a trade-off between the energy cost and the users’ thermal comfort is achieved. The proposed user-centric approach takes advantage of the novel paradigm of the Social Internet of Things to leverage a social consciousness and allow automated interactions between objects. Accordingly, the system automatically obtains the thermal profiles of both rooms and users. All these profiles are continuously updated based on the system experience and are then analysed through an optimization model to drive the selection of the most appropriate working times for HVACs. Experimental results in a real environment demonstrated the cognitive behaviour of the system which can adapt to users’ needs and ensure an acceptable comfort level while at the same time reducing energy costs compared to traditional usage

Numerical simulation of strongly nonlinear and dispersive waves using a Green-Naghdi model

We investigate here the ability of a Green-Naghdi model to reproduce strongly nonlinear and dispersive wave propagation. We test in particular the behavior of the new hybrid finite-volume and finite-difference splitting approach recently developed by the authors and collaborators on the challenging benchmark of waves propagating over a submerged bar. Such a configuration requires a model with very good dispersive properties, because of the high-order harmonics generated by topography-induced nonlinear interactions. We thus depart from the aforementioned work and choose to use a new Green-Naghdi system with improved frequency dispersion characteristics. The absence of dry areas also allows us to improve the treatment of the hyperbolic part of the equations. This leads to very satisfying results for the demanding benchmarks under consideration

Numerical Modelling Of The V-J Combinations Of The T Cell Receptor TRA/TRD Locus

T-Cell antigen Receptor (TR) repertoire is generated through rearrangements of V and J genes encoding α and β chains. The quantification and frequency for every V-J combination during ontogeny and development of the immune system remain to be precisely established. We have addressed this issue by building a model able to account for Vα-Jα gene rearrangements during thymus development of mice. So we developed a numerical model on the whole TRA/TRD locus, based on experimental data, to estimate how Vα and Jα genes become accessible to rearrangements. The progressive opening of the locus to V-J gene recombinations is modeled through windows of accessibility of different sizes and with different speeds of progression. Furthermore, the possibility of successive secondary V-J rearrangements was included in the modelling. The model points out some unbalanced V-J associations resulting from a preferential access to gene rearrangements and from a non-uniform partition of the accessibility of the J genes, depending on their location in the locus. The model shows that 3 to 4 successive rearrangements are sufficient to explain the use of all the V and J genes of the locus. Finally, the model provides information on both the kinetics of rearrangements and frequencies of each V-J associations. The model accounts for the essential features of the observed rearrangements on the TRA/TRD locus and may provide a reference for the repertoire of the V-J combinatorial diversity

A mathematical model for unsteady mixed flows in closed water pipes

We present the formal derivation of a new unidirectional model for unsteady mixed flows in non uniform closed water pipe. In the case of free surface incompressible flows, the \FS-model is formally obtained, using formal asymptotic analysis, which is an extension to more classical shallow water models. In the same way, when the pipe is full, we propose the \Pres-model, which describes the evolution of a compressible inviscid flow, close to gas dynamics equations in a nozzle. In order to cope the transition between a free surface state and a pressured (i.e. compressible) state, we propose a mixed model, the \PFS-model, taking into account changes of section and slope variation

The Borexino detector at the Laboratori Nazionali del Gran Sasso

Borexino, a large volume detector for low energy neutrino spectroscopy, is currently running underground at the Laboratori Nazionali del Gran Sasso, Italy. The main goal of the experiment is the real-time measurement of sub MeV solar neutrinos, and particularly of the mono energetic (862 keV) Be7 electron capture neutrinos, via neutrino-electron scattering in an ultra-pure liquid scintillator. This paper is mostly devoted to the description of the detector structure, the photomultipliers, the electronics, and the trigger and calibration systems. The real performance of the detector, which always meets, and sometimes exceeds, design expectations, is also shown. Some important aspects of the Borexino project, i.e. the fluid handling plants, the purification techniques and the filling procedures, are not covered in this paper and are, or will be, published elsewhere (see Introduction and Bibliography).Comment: 37 pages, 43 figures, to be submitted to NI

A tritium vessel cleanup experiment in TFTR

A simple tritium cleanup experiment was carried out in TFTR following the initial high power deuterium-tritium discharges in December 1993. A series of 34 ohmic and deuterium neutral beam fueled shots was used to study the removal of tritium implanted into the wall and limiters. A very large plasma was created in each discharge to ``scrub`` an area as large as possible. Beam-fueled shots at 2.5 to 7.5 MW of injected power were used to monitor tritium concentration levels in the plasma by detection of DT-neutrons. The neutron signal decreased by a factor of 4 during the experiment, remaining well above the expected T-burnup level. The amount of tritium recovered at the end of the cleanup was about 8% of the amount previously injected with high power DT discharges. The experience gained suggests that measurements of tritium inventory in the torus are very difficult to execute and require dedicated systems with overall accuracy of 1%