What are check dams made for? An historical perspective from the French experience

International audienceThe mitigation of torrent related hazards is an important issue in mountainous regions. Structural mitigation measures have been implemented on hill slopes and in streambeds for more than 150 years in all Europe. Check dams play a key role in these mitigation plans and can have highly variable functions (horizontal and vertical stabilization of streambeds, consolidation of hillslopes' toe, retention of sediments, modulations of high solid discharges, lowering of streambed slope, etc.). Thousands of structures had been built more than a century ago. Since their construction, land uses evolved, torrent control works, associated with reforestation, curtailed a part of the sediment production. According to field experience, defining the initial and current functions of some old structures can remain challenging in some cases. To better understand for which purposes thousands of these structures were built during the 19th and 20th centuries , we analyzed old books to determine: • what was the history of the comprehension of the processes involved in torrent related hazards? and; • how the use of check dams evolved to take into account this improving comprehension? i.e. how the human actions on watercourses co-evolved with scientific knowledge from the early 19th centuries to nowadays? The presentation does not aim to determine who, the first, addressed any scientific question: equivalent history and scientific works took place in all regions of the world at different time and the French were not the first to build check dams and to undertook watershed scale mitigation plans. But the French example is interesting because the torrent control works were planned in mountainous regions at the country scale (the Alps, the Pyrenees and the Massif Central). Initial plans were to reforest mountains, relying on civil engineering works if needed. Their implementation , through the French Mountain Lands' reforestation and grass seeding laws of 1860 and 1864, proved to be difficult for technical and sociological reasons. The Mountain lands' conservation and restoration law of 1882 aimed to better fit local issues. The idea of the presentation is thus to highlight how evolved the historical comprehension of torrential hazards and of the usefulness of check dams in miti-gation plans in a changing environment on the technical as well as on the sociological and regulatory points of view. Pioneering scientific and technical works on torrential hydraulics and check dams will be presented. Describing the global context that leads to French laws of 1860,1864 and 1882 will allow us to explain the extensive development of the works in more than a thousand of torrents and a hundred of big landslides. We then will discuss the evolution of technics during the beginning of the 20th century and the changes induced after WWII by the arrival of reinforced-concrete technics. We will conclude the presentation with a synthesis table aiming to highlight the different functions of check dams based on a description of their situations in the watershed, compare to other structures' situations and on shape criteria. This historical perspective will hopefully help people to better understand for which purposes some structures have been built in the past centuries and what lessons can be learnt from this assessment

Evaluation of Efficiency of Torrential Protective Structures With New BF-TOPSIS Methods

Decision-Aid Methods (DAMs) such as the CostBenefit Analysis (CBA) and the Analytical Hierarchy Process (AHP) help decision-makers to rank alternatives or to choose the best one among several potential ones

Imperfect information propagation-based integrated decision-aiding approach applied to assess torrential protective systems’ effectiveness

Depuis le 19ème siècle, de nombreux dispositifs de protection ont été implantés en montagne pour réduire le risque torrentiel. L'évaluation multi-échelle de leur efficacité est nécessaire pour comparer et choisir les stratégies de maintenance et de gestion de l’occupation des sols. Le chapitre I met en évidence les ambiguïtés du concept d’efficacité évalué selon plusieurs critères dans un contexte d’information imparfaite, issue de sources multiples, inégalement fiables. Pour aider l’évaluation multidimensionnelle, le problème de décision est décomposé en plusieurs sous-problèmes formulés, modélisés, traités puis intégrés. L’état de l’art du chapitre II permet de retenir les méthodes de la sûreté de fonctionnement (SdF) et d'aide à la décision (AD) basées sur le Raisonnement Évidentiel, associant les ensembles flous, les possibilités, les fonctions de croyance et la fusion d’information pour traiter chaque problème. Le chapitre III explicite le concept d'efficacité puis propose une adaptation des méthodes de la SdF à la formulation multi-échelle des problèmes. Le chapitre IV adapte les méthodes d'AD basées sur le Raisonnement Évidentiel, les améliore pour mieux représenter la connaissance disponible et évaluer la qualité d’une décision, et les associe. Le chapitre V propose une méthodologie séquentielle qui intègre ces méthodes pour évaluer les mesures de protection, de l’échelle de l’ouvrage à celle du bassin d’enjeux. Enfin, le chapitre VI discute les résultats, identifie les apports respectifs de l'intégration et des nouvelles méthodes, puis décrit les perspectives de déploiement opérationnel de la méthodologie développée.Many torrential protective check dams have been built in French mountainous areas since the 19th century. They aim to reduce risk in torrential watersheds. Analysis of their effectiveness is needed to assess residual risk and to choose the best maintenance strategy in a context of reduced budgets. Chapter I introduces main issues due both to definition of effectiveness concept and also the several criteria and system scales that have to be assessed. Moreover, required expertise is based on imperfect information, provided by several sources with different reliability levels. To help such decisions, this thesis proposes to break down general assessment into several smaller decision-making problems. In chapter II, dependability analysis tools and Evidential Reasoning based-decision-aiding methods (ER-DAMs), using fuzzy sets and possibility theories, are chosen to help individual decisions. Chapters III to V then introduce new developments. Effectiveness concept is first defined. A multi-scale dependability analysis helps to describe each decision-making problem. ER-DAMs are then adapted to help effectiveness assessment at each system’s scale. Technical improvements are provided to these methods for a better knowledge representation and final decision. Improved methods are then associated. Finally, individual problems and associated methods are integrated in a generic methodology to help torrential protective measures’ effectiveness assessment at watershed scale. The last chapter VI focuses on discussion of integrative aspects and of ER-DAMs’ specific developments. It gives some elements to improve methods but also to help operational implementation of the generic methodology

La méthode ANETO : un outil pour la prédétermination des débits de crue des bassins versants torrentiels des Pyrénées françaises

Pour améliorer la prévention et la protection contre les risques générés par les crues torrentielles en montagne, les acteurs locaux ont besoin de connaissances sur les différents processus mis en jeu, notamment sur l'évaluation des débits de crue. Les auteurs présentent ici une méthode combinant l'exploitation statistique des mesures hydrométriques et pluviométriques et la prise en compte de données climatologiques et géomorphologiques pour déterminer de façon plus réaliste les débits de crues des bassins versants torrentiels des Pyrénées françaises

Protection works against natural hazards: from failure analysis to effectiveness assessment

International audienc

Approche intégrée d’aide à la décision basée sur la propagation de l’imperfection de l’information – application à l’efficacité des mesures de protection torrentielle

Many torrential protective check dams have been built in French mountainous areas since the 19th century. They aim to reduce risk in torrential watersheds. Analysis of their effectiveness is needed to assess residual risk and to choose the best maintenance strategy in a context of reduced budgets. Chapter I introduces main issues due both to definition of effectiveness concept and also the several criteria and system scales that have to be assessed. Moreover, required expertise is based on imperfect information, provided by several sources with different reliability levels. To help such decisions, this thesis proposes to break down general assessment into several smaller decision-making problems. In chapter II, dependability analysis tools and Evidential Reasoning based-decision-aiding methods (ER-DAMs), using fuzzy sets and possibility theories, are chosen to help individual decisions. Chapters III to V then introduce new developments. Effectiveness concept is first defined. A multi-scale dependability analysis helps to describe each decision-making problem. ER-DAMs are then adapted to help effectiveness assessment at each system’s scale. Technical improvements are provided to these methods for a better knowledge representation and final decision. Improved methods are then associated. Finally, individual problems and associated methods are integrated in a generic methodology to help torrential protective measures’ effectiveness assessment at watershed scale. The last chapter VI focuses on discussion of integrative aspects and of ER-DAMs’ specific developments. It gives some elements to improve methods but also to help operational implementation of the generic methodology.Depuis le 19ème siècle, de nombreux dispositifs de protection ont été implantés en montagne pour réduire le risque torrentiel. L'évaluation multi-échelle de leur efficacité est nécessaire pour comparer et choisir les stratégies de maintenance et de gestion de l’occupation des sols. Le chapitre I met en évidence les ambiguïtés du concept d’efficacité évalué selon plusieurs critères dans un contexte d’information imparfaite, issue de sources multiples, inégalement fiables. Pour aider l’évaluation multidimensionnelle, le problème de décision est décomposé en plusieurs sous-problèmes formulés, modélisés, traités puis intégrés. L’état de l’art du chapitre II permet de retenir les méthodes de la sûreté de fonctionnement (SdF) et d'aide à la décision (AD) basées sur le Raisonnement Évidentiel, associant les ensembles flous, les possibilités, les fonctions de croyance et la fusion d’information pour traiter chaque problème. Le chapitre III explicite le concept d'efficacité puis propose une adaptation des méthodes de la SdF à la formulation multi-échelle des problèmes. Le chapitre IV adapte les méthodes d'AD basées sur le Raisonnement Évidentiel, les améliore pour mieux représenter la connaissance disponible et évaluer la qualité d’une décision, et les associe. Le chapitre V propose une méthodologie séquentielle qui intègre ces méthodes pour évaluer les mesures de protection, de l’échelle de l’ouvrage à celle du bassin d’enjeux. Enfin, le chapitre VI discute les résultats, identifie les apports respectifs de l'intégration et des nouvelles méthodes, puis décrit les perspectives de déploiement opérationnel de la méthodologie développée

Les ouvrages de protection contre les risques naturels : de l'analyse des défaillances à l'évaluation de l'efficacité

International audienc

EMISSION PHOTONIQUE DANS UN MICROSCOPE A EFFET TUNNEL. APPLICATION A L'ETUDE DE NANO-CONTACTS METAL/SEMICONDUCTEUR

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Protection structures against natural hazards: from failure analysis to effectiveness assessment

International audienceProtection structures aim to protect areas exposed to natural hazards. For instance, several clusters of check dams are located in the headwaters of a watershed, each having specific functions. Their structural, functional, and economic effectiveness must be assessed to assist decision makers in deciding on maintenance actions. Nevertheless, expert assessment generally focuses on a single check dam. It is based on the evaluation of several field indicators that are aggregated by experts. This paper aims to show how methods extracted from industry, such as dependability analysis and decision-making approaches, can be used to help formalize expert assessment with expert knowledge taken into account. For this purpose the formal methods are reviewed and their potential application introduced. This paper focuses on the use of indicators and criteria in various objective decision-making tools. For example, it compares the Analytic Hierarchic Process and the ELECTRE TRI methods to assess the functional effectiveness of a cluster of check dams

A quoi servent les barrages de corrections torrentielles? Une perspective historique tirée de l'expérience française

International audienceThe mitigation of torrent related hazards is an important issue in mountainous regions. Structural mitigation measures have been implemented on hill slopes and in streambeds for more than 150 years in all Europe. Check dams play a key role in these mitigation plans and can have highly variable functions (horizontal and vertical stabilization of streambeds, consolidation of hillslopes' toe, retention of sediments, modulations of high solid discharges, lowering of streambed slope, etc.). Thousands of structures had been built more than a century ago. Since their construction, land uses evolved, torrent control works, associated with reforestation, curtailed a part of the sediment production. According to field experience, defining the initial and current functions of some old structures can remain challenging in some cases. To better understand for which purposes thousands of these structures were built during the 19th and 20th centuries , we analyzed old books to determine: • what was the history of the comprehension of the processes involved in torrent related hazards? and; • how the use of check dams evolved to take into account this improving comprehension? i.e. how the human actions on watercourses co-evolved with scientific knowledge from the early 19th centuries to nowadays? The presentation does not aim to determine who, the first, addressed any scientific question: equivalent history and scientific works took place in all regions of the world at different time and the French were not the first to build check dams and to undertook watershed scale mitigation plans. But the French example is interesting because the torrent control works were planned in mountainous regions at the country scale (the Alps, the Pyrenees and the Massif Central). Initial plans were to reforest mountains, relying on civil engineering works if needed. Their implementation , through the French Mountain Lands' reforestation and grass seeding laws of 1860 and 1864, proved to be difficult for technical and sociological reasons. The Mountain lands' conservation and restoration law of 1882 aimed to better fit local issues. The idea of the presentation is thus to highlight how evolved the historical comprehension of torrential hazards and of the usefulness of check dams in mitigation plans in a changing environment on the technical as well as on the sociological and regulatory points of view. Pioneering scientific and technical works on torrential hydraulics and check dams will be presented. Describing the global context that leads to French laws of 1860,1864 and 1882 will allow us to explain the extensive development of the works in more than a thousand of torrents and a hundred of big landslides. We then will discuss the evolution of technics during the beginning of the 20th century and the changes induced after WWII by the arrival of reinforced-concrete technics. We will conclude the presentation with a synthesis table aiming to highlight the different functions of check dams based on a description of their situations in the watershed, compare to other structures' situations and on shape criteria. This historical perspective will hopefully help people to better understand for which purposes some structures have been built in the past centuries and what lessons can be learnt from this assessment