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

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

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

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

Taking into account protective works in land-use planning for mountain torrential floods: state of the art of the present French practices

International audienceIn 1995, a law stated a common regulatory natural risk zoning for French municipalities through a land-use planning procedure called Risk Prevention Plan (PPR). In mountain valleys and especially within torrential watersheds, considering protective structures in those plans is an actual concern. Those protections do have an effect on phenomena and modify hazard and risk levels. This paper gives an overview on how torrential protective works are taken into account in present risk prevention plans. To carry out this study, 53 recent risk prevention plans over 11 French mountain departments were selected and analyzed through a common analysis grid. Torrential protection works are taken into account in more than one third of analyzed plans. Protections mostly considered are dikes, bank protections, check-dams and sediment traps. Modalities of integration of these structures vary from one plan to another, influencing both hazard and regulatory zoning. Results also show a wide range of practices between departments and even inside them. Conclusions brought out enhance knowledge about actual practices which were not sufficiently known so far. Findings and new additional recommendations will be included in a future PPR methodological guide exclusively suited for torrential context, which is currently still missing

Taking into account protective works in land-use planning for mountain torrential floods: state of the art of the present French practices

International audienceIn 1995, a law stated a common regulatory natural risk zoning for French municipalities through a land-use planning procedure called Risk Prevention Plan (PPR). In mountain valleys and especially within torrential watersheds, considering protective structures in those plans is an actual concern. Those protections do have an effect on phenomena and modify hazard and risk levels. This paper gives an overview on how torrential protective works are taken into account in present risk prevention plans. To carry out this study, 53 recent risk prevention plans over 11 French mountain departments were selected and analyzed through a common analysis grid. Torrential protection works are taken into account in more than one third of analyzed plans. Protections mostly considered are dikes, bank protections, check-dams and sediment traps. Modalities of integration of these structures vary from one plan to another, influencing both hazard and regulatory zoning. Results also show a wide range of practices between departments and even inside them. Conclusions brought out enhance knowledge about actual practices which were not sufficiently known so far. Findings and new additional recommendations will be included in a future PPR methodological guide exclusively suited for torrential context, which is currently still missing

A survey on protection works databases used at the Alpine Space level: analysis of contents and state of the art related to protection works effectiveness assessment

Natural phenomena in mountainous areas put people and assets at risk. Risk is classically assessed as a combination of hazard and vulnerability. Hazard relates to the intensity and frequency of phenomena, whereas vulnerability concerns damage and values assessment. Risk reduction measures and strategies are based on non-structural measures such as land-use control through risk zoning maps, preventive information and structural measures such as civil engineering protection works (check-dams, snow nets, etc.). To ensure prevention and limit risks, protection works have an essential role to reduce both causes and effects of phenomena. Decision-aid tools are needed for long term monitoring and management of protection works. Assessing their effectiveness considering both their structural state and functional abilities is challenging. This survey gives a picture in 2014 of the existing processes for protection works monitoring (databases) in France (ONF RTM1), Austria (TAC2) and Italy (Autonomous Region of Valle d’Aosta and Autonomous Province of Bolzano). We analyze options taken in existing databases to monitor effectiveness indicators. We compare the use of collected data during the monitoring of protection works. Finally, we identify best practices used in the monitoring of protection systems that should be included in future upgrading of databases. The survey was divided in 3 steps: i) development of a questionaire related to protection work databases and the assessment of effectiveness and efficiency concepts, ii) analysis of existing databases, iii) formulation of recommendations. The comparison of databases gives the following global picture. Having an overview of existing protection systems and assessing their condition are common initial objectives of databases. Decision support objective to plan interventions is not clearly expressed. Indicator definitions to describe works are different. Protection works assessment is based on expert field analysis. Structural condition is always assessed unlike functional ability. Comparing protection works with exposed elements they protect and natural hazards they reduce is not registered in databases. For a better design, interoperability and management of databases on protection works and their effectiveness, it is recommended to i) enlarge the survey to all Europe, ii) establish a common expert English glossary, iii) improve database management capacities (definition of objectives, organization, etc.), iv) upgrade existing databases from a registration tool to a decision-aid tool for a relevant protection works management

Evaluation integree de l'efficience des ouvrages de protection contre les risques naturels

International audienceProtection measures limit direct and indirect damages caused by natural hazards in mountains. To choose between possible actions, experts have to assess their technical performance but also economic aspects of the problem assessing their efficiency. Several decision-aid methods exist to assess these two effectiveness levels. To assess efficiency, the application is limited to implement to as theoretical study case and to criticize the most common method (Cost Benefit Analysis). To assess the technical performance, a real study case of Analytic Hierarchy Process, the simplest of MultiCriteria Decision Analysis methods, shows its limits. Considering decision scales and information quality remain two important issues. In the context of natural hazard in the mountains, protection measures effectiveness assessment has to integrate the different levels of this concept, the different aid-decision methods and the different methods of information quality formalization and propagation.Les mesures de protection limitent les dommages directs et indirects dus aux phénomènes naturels en montagne. Pour décider des actions à mener, l’expert évalue leur niveau de performance technique mais doit aussi considérer la composante économique en évaluant leur efficience. Plusieurs méthodes d’aide à la décision permettent d’évaluer ces deux niveaux d’efficacité. Pour l’évaluation de l’efficience, l’application se limite à la mise en oeuvre sur un cas d’étude théorique simplifié et la critique de la plus utilisée d’entre elles, l’Analyse Coûts-Bénéfices. Pour l’évaluation de la performance technique, un cas d’application réel de la méthode d’Analyse MultiCritères Hiérarchique, la plus simple des méthodes d’Aide MultiCritères à la décision, met en évidence ses limites. La prise en compte des échelles de décision et de l’imperfection de l’information reste un problème important. L’évaluation de l’efficacité des ouvrages de protection contre les risques naturels doit intégrer les différents niveaux d’efficacité, les différentes méthodes d’aide à la décision et les différentes méthodes de formalisation et de propagation de l’imperfection de l’information

Évaluation intégrée de l’efficience des ouvrages de protection contre les risques naturels en montagne

International audienceProtection measures limit direct and indirect damages caused by natural hazards in mountains. To choose between possible actions, experts have to assess their technical performance but also economic aspects of the problem assessing their efficiency. Several decision-aid methods exist to assess these two effectiveness levels. To assess efficiency, the application is limited to implement to as theoretical study case and to criticize the most common method (Cost Benefit Analysis). To assess the technical performance, a real study case of Analytic Hierarchy Process, the simplest of MultiCriteria Decision Analysis methods, shows its limits. Considering decision scales and information quality remain two important issues. In the context of natural hazard in the mountains, protection measures effectiveness assessment has to integrate the different levels of this concept, the different aid-decision methods and the different methods of information quality formalization and propagation.Les mesures de protection limitent les dommages directs et indirects dus aux phénomènes naturels en montagne. Pour décider des actions à mener, l’expert évalue leur niveau de performance technique mais doit aussi considérer la composante économique en évaluant leur efficience. Plusieurs méthodes d’aide à la décision permettent d’évaluer ces deux niveaux d’efficacité. Pour l’évaluation de l’efficience, l’application se limite à la mise en oeuvre sur un cas d’étude théorique simplifié et la critique de la plus utilisée d’entre elles, l’Analyse Coûts-Bénéfices. Pour l’évaluation de la performance technique, un cas d’application réel de la méthode d’Analyse MultiCritères Hiérarchique, la plus simple des méthodes d’Aide MultiCritères à la décision, met en évidence ses limites. La prise en compte des échelles de décision et de l’imperfection de l’information reste un problème important. L’évaluation de l’efficacité des ouvrages de protection contre les risques naturels doit intégrer les différents niveaux d’efficacité, les différentes méthodes d’aide à la décision et les différentes méthodes de formalisation et de propagation de l’imperfection de l’information