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Le projet HYDRODEMO a pour objectif de mieux connaître les risques liés aux crues torrentielles dans les Alpes du Nord et de pouvoir mieux s’en prémunir. Le manque d’observations hydrométéorologiques dans les Alpes du Nord, que ce soit en termes de forçages météorologiques ou hydrologiques, limite fortement nos connaissances sur ce type d'aléa. Afin de combler ce manque de connaissance, l'action 4 du projet HYDRODEMO, objet de ce présent rapport, consiste à appliquer des outils de modélisation hydrologique à des petits bassins versants torrentiels instrumentés pour, d'une part, tenter d'en caractériser et reproduire le fonctionnement, et, d'autre part, définir une méthodologie de transposition aux bassins versants non instrumentés sous la forme d'un travail de régionalisation des paramètres des modèles. L'objectif associé à cette régionalisation est d'étudier la possibilité de la mise en œuvre des modèles sur les bassins versants non instrumentés, afin d'y permettre la connaissance de valeurs statistiques de crues.Pour répondre à ces objectifs, ce rapport présente l'application de deux modèles hydrologiques, le modèle semi-distribué MORDOR-SD adapté aux zones de montagne (modules neige et glace) et le modèle distribué SMASH (Spatially-distributed Modelling and ASsimilation for Hydrology), plateforme développée par INRAE avec le soutien du Ministère de la Transition Ecologique et mise en œuvre dans le dispositif national Vigicrues Flash, dont l'adaptation aux zones de montagne a pu être réalisée dans le cadre du projet HYDRODEMO, par le biais notamment de l'introduction d'un module neige. Pour les deux modèles, le développement de la méthodologie et l'évaluation des performances sont effectués sur un ensemble de bassins versants torrentiels jaugés des Alpes du Nord. Nous montrons en particulier la sensibilité des performances aux types de forçage météorologique et à la stratégie d'estimation des paramètres (calibration à partir des mesures de débit versus méthode de régionalisation). Le travail de régionalisation mené pour les deux modèles permet d'envisager des pistes pour leur mise en œuvre sur des bassins versants non jaugés.

International audience; Two national early warning services have been operationally implemented in France as a result of research undertaken in recent years. APIC, a warning service for heavy rainfall set up in 2011 by Météo-France, issues warnings when the current rainfall exceeds climatological thresholds at the scale of a municipal territory. Vigicrues Flash, a flash flood warning service set up by the Ministry in charge of Environment in 2017, issues warnings when flood forecasts exceed reference flood quantiles (which were estimated from streamflow simulated time series using the same hydrological model) at the scale of small catchments. These two services enable crisis managers to better mitigate flood risk impacts. They are based on the same web platform for subscription, warning dissemination and hazard map display of the extreme events over the last 72 h. Several major enhancements are being implemented by the beginning of 2021: (i) the technical and ergonomic improvement of the web platform; (ii) the dissemination and communication of the warning services to intermunicipal authorities and public utility organisations involved in crisis management; (iii) the dissemination and communication of the hazard map display service to the general public; (iv) the improvement of the radar-gauge quantitative precipitation estimate used as input in the APIC service, to cover the whole french metropolitan territory; (v) the improvement of the hydrological distributed model in Vigicrues Flash ingesting the radar-gauge quantitative precipitation estimate, for better performance, robustness and an extended coverage of the flash flood warning service.; Météo-France et délivre des avertissements lorsque les précipitations en cours revêtent un caractère exceptionnel sur une commune ou les communes environnantes, par rapport aux données climatologiques de référence. Vigicrues Flash, service d'avertissement sur les crues soudaines, a été ouvert par le ministère en charge de l'environnement en 2017 et délivre des avertissements en cas de prévision hydrologique revêtant un caractère exceptionnel sur un ou plusieurs bassins versants élémentaires, par rapport aux données hydrologiques de référence (quantiles de crues estimés à partir des chroniques de débit simulé avec le même modèle hydrologique). Ces deux services, proposés aux gestionnaires de crise, bénéficient de la même plateforme de prise d'abonnement, d'envoi et de visualisation des avertissements. D'importantes évolutions sont prévues d'ici à début 2021 : (i) l'évolution technique et ergonomique de la plateforme internet commune aux deux services ; (ii) l'ouverture des services aux intercommunalités, aux organismes d'utilité publique impliqués dans la gestion de crise ; (iii) l'ouverture en visualisation pour le grand public ; (iv) le changement du produit de lame d'eau alimentant le service APIC, permettant la couverture d'une plus grande partie du territoire ; (v) l'évolution du modèle hydrologique distribué de Vigicrues Flash et le changement de la lame d'eau l'alimentant, permettant d'étendre la couverture et la robustesse du service.

In most cases, natural hazards encountered in mountainous areas are largely dependent on precipitations: flash floods, debris flows, landslides, rock falls, snow avalanches. However, the knowledge of rainfall quantities still remains a tricky issue: the available rain-gauges are in a limited number and most often located in the valleys, and the radar rainfall estimates have to deal with a lot of problems due to the relief and the difficulty to distinguish the different types of hydrometeors (snow, hail, rain). In this context, the “RHYTMME” project (Westrelin and al., 2010) deals with two main issues:-Providing an accurate radar rainfall information in mountainous areas. -Developing a real-time hazards warning system based on this information. In this context, a X-band doppler dual polarized radar network is currently implemented in the French South Alps. It completes a pre-existing radar already installed on the Mont Vial summit since 2008 (Hydrix® technology developed by the Novimet company, and tested in a previous project).The present communication focuses on the flash flood warning system only. This system is based on the AIGA method developed for the ungauged catchments by IRSTEA and METEO-FRANCE for a decade. (Javelle and al, 2010) It is a simple event-based distributed hydrological model transforming rainfalls into discharges. The evaluation of the model quality is always a delicate task when no data are available (ungauged basins). Two ways are explored to evaluate the AIGA method performance on different small catchments located on a 17000 km² area on the South of France. On the one hand, the real-time RHYTMME platform is used. For each important storm event, the platform end-users composed by different public services (like “Restoration of Mountainous Territories (RTM)) realize an on-field survey. This users group tests the platform in real-time. The rainfall is estimated by the X-band radar and the calculated discharges are compared to damages reported by end-users. On the other hand, in order to improve the AIGA method, an historical data-base of flood damages reports, covering the 1997-2006 period, is used. These data have been collected by local authorities (RTM) and give us some information on 139 ungauged locations. Using radar rainfall data provided by METEO-FRANCE for the 1997-2006 period, the discharges are modelled and compared to these observed damages.. We are then able to evaluate, for each watershed, a threshold discharge above which most damages occur. The main advantage of this historical approach is the availability of many events in the data-base, which enabled us to calibrate the threshold discharges thanks to the optimisation of a contingency criterion (the CSI index).

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN [Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN; Le génie végétal se révèle une solution naturelle, efficace et durable pour lutter contre les problèmes d'érosion des berges. Comment ces techniques peuvent-elles s'appliquer aux berges de cours d’eau soumises à des sécheresses estivales ? Cet article se propose d’étudier les potentialités d'espèces ripicoles encore peu exploitées aujourd'hui, les Tamaricaceae, présentant des facultés spécifiques de résistance à la sécheresse tout en ayant des capacités de stabilisation des berges.

International audience; The real-time vision of a large portion of French rivers is not a coloured one, not even a black and white, but a blind one, du to the large number of basins which are not monitored. The event of June 2010 in Southern France, where 25 people died during the flood of the Nartuby and Argens rivers gives a dramatic example of this blind vision. In such a context a simple insight, aiming at providing flood alerts rather than pretending to represent exactly the physical process at stake in the catchment, seems welcomed. The aim of this study is to assess the ability of a simple conceptual and parsimonious rainfall-runoff model to deliver flood alerts in ungauged catchments. We use a downward approach: the model is calibrated on gauged catchments and its performances are checked on nested catchments which are not used for the calibration. The model is calibrated over 20 catchments of southern France with areas ranging from 150 km² to 2170 km². The rainfall information is provided by a radar network at an hourly time-step for 15 events that have occurred between 2005 and 2008. The "ungauged" catchments used for the model evaluation are 47 nested basins located within the 20 calibration catchments. We derive the model parameters for these ungauged catchments, from the gauged ones. The model used belongs to the GR models family developed at the Cemagref institute. It works on en event basis thank to a production parameter S and two routing parameters: a shape parameter B and a lag parameter C. Our knowledge of the production parameter benefits from a previous regionalisation work based on several characteristics of the catchments such as the description of their drainage network, the ground-water typology and a climatic variable. The model calibration rests upon the production parameter only. We implement two versions of the model: a lumped one and a distributed one. The results of this downward approach show that the model tested here is able to deliver successful flood alerts in ungauged areas. The distributed version performs slightly better than the lumped version. This study also show that fully distributing the routing parameters results in better alerts than using uniform routing parameters in the distributed version. To fully assess the performance of the model, further evaluation should be carried out in an operational mode, i.e. using an initialisation procedure to determine the value of the S parameter at the beginning of each event instead of using a calibrated value. We anticipate this study by checking how well the calibrated S correlate with the parameter of a continuous soil moisture accounting model run at a daily time-step. The correlation being better in the case of the distributed version of the model, this version seems hence quite promising for an operational use.