Category Archives: Theses_completed

Marc Choffet: Cost of Natural Hazards to Building and Influence of Risk Factors in the Context of Building Insurance

Marc Choffet
Director: Prof. Michel Jaboyedoff
Jury: Prof. Michel Jaboyedoff, Prof. Eric Verrecchia, Prof. Franco Romerio, Prof. Jean Ruegg, Dr. Markus Imhof

In Switzerland, the annual cost of damage by natural elements has been increasing for several years despite the introduction of protective measures. Mainly induced by material destruction, building insurance companies have to pay the majority of this cost. In many European countries, governments and insurance companies consider prevention strategies to reduce vulnerability. In Switzerland, since 2004, the cost of damage due to natural hazards has surpassed the cost of damage due to fire; a traditional activity of the Cantonal Insurance company (ECA). Therefore, the strategy for efficient fire prevention incorporates a reduction of the vulnerability of buildings. The thesis seeks to illustrate the relevance of such an approach when applied to the damage caused by natural hazards. It examines the role of insurance place and its involvement in targeted prevention of natural disasters.

Integrated risk management involves a faultless comprehension of all risk parameters. The first part of the thesis is devoted to the theoretical development of the key concepts that influence risk management, such as: hazard, vulnerability, exposure or damage. The literature on this subject, very prolific in recent years, was taken into account and put in perspective in the context of this study.

Among the risk parameters, it is shown in the thesis that vulnerability is a factor that we can influence efficiently in order to limit the cost of damage to buildings. This is confirmed through the development of an analysis method. This method has led to the development of a tool to assess damage to buildings by flooding. The tool, designed for the property insurer or owner, proposes several steps, namely:

  • Vulnerability and damage potential assessment;
  • Proposals for remedial measures and risk reduction from an analysis of the costs of a potential flood;
  • Adaptation of a global strategy in high-risk areas based on the elements at risk.

The final part of the thesis is devoted to the study of a hail event in order to provide a better understanding of damage to buildings. For this, two samples from the available claims data were selected and analysed in the study. The results allow the identification of new trends. A second objective of the study was to develop a hail model based on the available data. The model simulates a random distribution of intensities and coupled with a risk model, proposes a simulation of damage costs for the determined study area.

Karen Sudmeier-Rieux: On risk, resilience and vulnerability of mountain communities in Central-Eastern Nepal

Karen Sudmeier-Rieux
Director: Prof. Michel Jaboyedoff
Jury: Dr. Ronald Jaubert, Dr. JC Gaillard, Dr. Markus Zimmermann, Dr. Knut Falk

In Nepal, landslides are one of the major natural hazards after epidemics, killing over 100 persons per year. However, this figure is an underreported reflection of the actual impact that landslides have on livelihoods and food security in rural Nepal. With predictions of more intense rainfall patterns, landslide occurrence in the Himalayas is likely to increase and continue to be one of the major impediments to development. Due to the remoteness of many localities and lack of resources, responsibilities for disaster preparedness and response in mountain areas usually lie with the communities themselves. Everyday life is full of risk in mountains of Nepal. This is why mountain populations, as well as other populations living in harsh conditions have developed a number of coping strategies for dealing with adverse situations. Perhaps due to the dispersed and remote nature of landslides in Nepal, there have been few studies on vulnerability, coping- and mitigation strategies of landslide affected populations. There are also few recommendations available to guide authorities and populations how to reduce losses due to landslides in Nepal, and even less so, how to operationalize resilience and vulnerability.

Many policy makers, international donors, NGOs and national authorities are currently asking what investments are needed to increase the so-called ‘resilience’ of mountain populations to deal with climate risks. However, mountain populations are already quite resilient to seasonal fluctuations, temperature variations, rainfall patterns and market prices. In spite of their resilience, they continue to live in places at risk due to high vulnerability caused by structural inequalities: access to land, resources, markets, education. This interdisciplinary thesis examines the concept of resilience by questioning its usefulness and validity as the current goal of international development and disaster risk reduction policies, its conceptual limitations and its possible scope of action. The goal of this study is two-fold: to better define and distinguish factors and relationships between resilience, vulnerability, capacities and risk; and to test and improve a participatory methodology for evaluating landslide risk that can serve as a guidance tool for improving community-based disaster risk reduction. The objective is to develop a simple methodology that can be used by NGOs, local authorities and communities to reduce losses from landslides.

Through its six case studies in Central-Eastern Nepal, this study explores the relation between resilience, vulnerability and landslide risk based on interdisciplinary methods, including geological assessments of landslides, semi-structured interviews, focus groups and participatory risk mapping. For comparison, the study sites were chosen in Tehrathum, Sunsari and Dolakha Districts of Central/Eastern Nepal, to reflect a variety of landslide types, from chronic to acute, and a variety of communities, from very marginalized to very high status. The study uses the Sustainable Livelihoods Approach as its conceptual basis, which is based on the notion that access and rights to resources (natural, human/institutional, economic, environmental, physical) are the basis for coping with adversity, such as landslides. The study is also intended as a contribution to the growing literature and practices on Community Based Disaster Risk Reduction specifically adapted to landslide- prone areas.

In addition to the six case studies, results include an indicator based methodology for assessing and measuring vulnerability and resilience, a composite risk assessment methodology, a typology of coping strategies and risk perceptions and a thorough analysis of the relation between risk, vulnerability and resilience. The methodology for assessing vulnerability, resilience and risk is relatively cost-effective and replicable in a low-data environment. Perhaps the major finding is that resilience is a process that defines a community’s (or system’s) capacity to rebound following adversity but it does not necessarily reduce vulnerability or risk of this community), which require addressing more structural issues related to poverty. Therefore, conclusions include a critical view of resilience as a main goal of international development and disaster risk reduction policies. It is a useful concept in the context of recovery after a disaster but it needs to be addressed in parallel with vulnerability and risk.

This research was funded by an interdisciplinary grant (#26083591) from the Swiss National Science Foundation for the period 2009-2011 and a seed grant from the Faculty of Geosciences and Environment at the University of Lausanne in 2008.

Andrea Pedrazzini: Characterization of gravitational rock slope deformations at different spatial scales based on field, remote sensing and numerical approaches.

Andrea Pedrazzini
Director: Prof. Michel Jaboyedoff
Jury: Prof. Torsten Venneman, Dr. Marc-Henri Derron, Dr. Federico Agliardi, Prof. Masahiro Chigira, Prof. Giovanni Crosta

Rock slope instabilities such as rock slides, rock avalanche or deep-seated gravitational slope deformations are widespread in Alpine valleys. These phenomena represent at the same time a main factor that control the mountain belts erosion and also a significant natural hazard that creates important losses to the mountain communities. However, the potential geometrical and dynamic connections linking outcrop and slope-scale instabilities are often unknown. A more detailed definition of the potential links will be essential to improve the comprehension of the destabilization processes and to dispose of a more complete hazard characterization of the rock instabilities at different spatial scales.

In order to propose an integrated approach in the study of the rock slope instabilities, three main themes were analysed in this PhD thesis: (1) the inventory and the spatial distribution of rock slope deformations at regional scale and their influence on the landscape evolution, (2) the influence of brittle and ductile tectonic structures on rock slope instabilities development and (3) the characterization of hazard posed by potential rock slope instabilities through the development of conceptual instability models.

To prose and integrated approach for the analyses of these topics, several techniques were adopted. In particular, high resolution digital elevation models revealed to be fundamental tools that were employed during the different stages of the rock slope instability assessment. A special attention was spent in the application of digital elevation model for detailed geometrical modelling of past and potential instabilities and for the rock slope monitoring at different spatial scales. Detailed field analyses and numerical models were performed to complete and verify the remote sensing approach.

In the first part of this thesis, large slope instabilities in Rhone valley (Switzerland) were mapped in order to dispose of a first overview of tectonic and climatic factors influencing their distribution and their characteristics. Our analyses demonstrate the key influence of neotectonic activity and the glacial conditioning on the spatial distribution of the rock slope deformations. Besides, the volumes of rock instabilities identified along the main Rhone valley, were then used to propose the first estimate of the postglacial denudation and filling of the Rhone valley associated to large gravitational movements.

In the second part of the thesis, detailed structural analyses of the Frank slide and the Sierre rock avalanche were performed to characterize the influence of brittle and ductile tectonic structures on the geometry and on the failure mechanism of large instabilities. Our observations indicated that the geometric characteristics and the variation of the rock mass quality associated to ductile tectonic structures, that are often ignored landslide study, represent important factors that can drastically influence the extension and the failure mechanism of rock slope instabilities.

In the last part of the thesis, the failure mechanisms and the hazard associated to five potential instabilities were analysed in detail. These case studies clearly highlighted the importance to incorporate different analyses and monitoring techniques to dispose of reliable and hazard scenarios. This information associated to the development of a conceptual instability model represents the primary data for an integrated risk management of rock slope instabilities.

 

 

Thierry Oppikofer: Detection, analysis and monitoring of slope movements by high-resolution digital elevation models.

Thierry Oppikofer
Director: Prof. Michel Jaboyedoff
Jury: Prof. Jean-Luc Epard, Prof. Torsten Vennemann, Dr. Marc-Henri Derron, Prof. Giovanni Crosta, Prof. Doug Stead, Dr. Lars Harald Blikra

Slope movements, such as rockfalls, rockslides, shallow landslides or debris flows, are frequent in many mountainous areas. These natural hazards endanger the inhabitants and infrastructures making necessary to assess the hazard and risk caused by these phenomena. This PhD thesis explores various approaches using digital elevation models (DEMs) – and particularly high-resolution DEMs created by aerial or terrestrial laser scanning (TLS) – that contribute to the assessment of slope movement hazard at regional and local scales.

The regional detection of areas prone to rockfalls and large rockslides uses different morphologic criteria or geometric instability factors derived from DEMs, i.e. the steepness of the slope, the presence of discontinuities that enable a sliding mechanism and the denudation potential. The combination of these factors leads to a map of susceptibility to rockfall initiation that is in good agreement with field studies as shown with the example of the Little Mill Campground area (Utah, USA). Another case study in the Illgraben catchment in the Swiss Alps highlighted the link between areas with a high denudation potential and actual rockfall areas.

Techniques for a detailed analysis and characterization of slope movements based on high-resolution DEMs have been developed for specific, localized sites, i.e. ancient slide scars, present active instabilities or potential slope instabilities. The analysis of the site’s characteristics mainly focuses on rock slopes and includes structural analyses (orientation of discontinuities); estimation of spacing, persistence and roughness of discontinuities; failure mechanisms based on the structural setting; and volume calculations. For the volume estimation a new 3D approach was tested to reconstruct the topography before a landslide or to construct the basal failure surface of an active or potential instability. The rockslides at Åknes, Tafjord and Rundefjellet in western Norway were principally used as study sites to develop and test the different techniques.

The monitoring of slope instabilities investigated in this PhD thesis is essentially based on multi-temporal (or sequential) high-resolution DEMs, in particular sequential point clouds acquired by TLS. The changes in the topography due to slope movements can be detected and quantified by sequential TLS datasets, notably by shortest distance comparisons revealing the 3D slope movements over the entire region of interest. A detailed analysis of rock slope movements is based on the affine transformation between an initial and a final state of the rock mass and its decomposition into translational and rotational movements. Monitoring using TLS was very successful on the fast-moving Eiger rockslide in the Swiss Alps, but also on the active rockslides of Åknes and Nordnesfjellet (northern Norway). One of the main achievements on the Eiger and Åknes rockslides is to combine the site’s morphology and structural setting with the measured slope movements to coherent instability models. Both case studies also highlighted a strong control of the structures in the rock mass on the sliding directions. TLS was also used to monitor slope movements in soils, such as landslides in sensitive clays in Québec (Canada), shallow landslides on river banks (Sorge River, Switzerland) and a debris flow channel (Illgraben).

The PhD thesis underlines the broad uses of high-resolution DEMs and especially of TLS in the detection, analysis and monitoring of slope movements. Future studies should explore more in depth the different techniques and approaches developed and used in this PhD, improve them and better integrate the findings in current hazard assessment practices and in slope stability models.

Pascal Horton: Improvements and global optimization of the analogue method for statistical precipitations forecasting.

Pascal Horton
Directors: Prof. Michel Jaboyedoff, Prof. Charles Obled
Jury: Prof. Francois Bussy, Dr. Dominique Berod, Dr. Daniel Cattani, Dr. Vincent Fortin

The upper Rhone catchment is sometimes subject to heavy precipitation that can eventually result in floods. The MINERVE project, to which this work belongs, aims at providing tools for flood forecasting and management. For this purpose, actions can be undertaken on dam storage, but this requires forecasting precipitation accurately days beforehand. This is currently done by the numerical weather prediction model of MétéoSuisse. However, due to large uncertainties in the forecasting of extreme events, it was decided that a parallel forecast based on a statistical approach could complement the information available.

Therefore, we adapted a technique of statistical precipitation forecasting, namely the analogue method, to the alpine context of our catchment. Several parameterizations of the method have been documented and calibrated.

A substantial part of this study was devoted to programming a forecasting software, which was called Atmoswing. It is designed to process automatically forecasts by means of the analogue method, and to provide a tool for visualizing the results on maps and graphs. It can process many different versions of the analogue method. The software has been operational since mid-2011, and has allowed us to confirm the interest of prediction by analogy.

As the method is applied here to a new geographical context, a large number of synoptic variables were evaluated. We then confirmed the relevance of the traditional two levels of analogy, which are related first to the atmospheric circulation, and next to the humidity flux, while making improvements to them. As a result, we created new parameterizations that have better forecasting skills than the reference methods considered so far. We also evaluated other improvements, such as the introduction of a shifting time window to find better synoptic analogues at other hours of the day, which show some potential. A 6-hourly time step forecast has been evaluated and was found to bring useful information on precipitation characteristics.

Finally, we introduced a technique of global optimization: genetic algorithms. These were found to be able to calibrate the analogue method by considering jointly all parameters of the different analogy levels. With that kind of tool we can approach an objectively optimal parameterization.

As the choice of atmospheric levels and time windows is automated, this technique can result in a gain of time, even if it is relatively demanding in calculations. Thus we were able to improve the analogue method, and to add new degrees of freedom.

 

Améliorations et optimisation globale de la méthode des analogues pour la prévision statistique des précipitations.

Développement d’un outil de prévision et application opérationnelle au bassin du Rhône à l’amont du Léman.

Le bassin du Rhône à l’amont du Léman peut être sujet à de fortes précipitations en mesure de provoquer des crues significatives. L’objectif du projet MINERVE dans lequel s’inscrit le présent travail consiste à fournir des outils pour la prévision et la gestion des crues par des actions préventives sur les aménagements hydroélectriques à accumulation. Pour satisfaire ce dernier, il est nécessaire de prévoir au mieux les cumuls de précipitations pour les jours suivants. Ceci est actuellement effectué par le modèle numérique de prévision de MétéoSuisse ; mais, en raison des grandes incertitudes liées à la quantification des événements extrêmes, il a été décidé qu’une approche parallèle de nature statistique pourrait compléter l’information disponible.

Ainsi, nous avons adapté la méthode des analogues, qui est une technique de prévision statistique des précipitations, au contexte alpin du bassin d’étude. Pour ce faire, plusieurs paramétrisations de la méthode ont été documentées et calibrées. Afin de prendre en main la méthode, nous avons effectué de multiples analyses paramétriques sur les variables synoptiques, mais également sur la constitution de groupements pluviométriques.

Une partie conséquente de cette étude a été consacrée à la programmation d’un logiciel de prévision automatique par la méthode des analogues, ainsi qu’à un outil de visualisation des résultats sous forme de cartes et graphiques. Ce logiciel, nommé Atmoswing, permet d’implémenter un grand nombre de méthodes différentes de prévision par analogie. L’outil est opérationnel depuis mi-2011 et nous a permis de confirmer l’intérêt de la prévision par analogie.

La méthode étant ici appliquée à un nouveau contexte, un grand nombre de variables synoptiques ont été évaluées. Nous avons alors confirmé l’intérêt des deux niveaux d’analogie sur la circulation atmosphérique et sur le flux d’humidité, tout en apportant des améliorations à celles-ci. Il en résulte des paramétrisations présentant des scores de performance supérieurs aux méthodes de référence considérées. Nous avons également évalué d’autres améliorations, comme l’introduction d’une fenêtre temporelle glissante afin de rechercher de meilleures analogies synoptiques à d’autres heures de la journée, ce qui s’est avéré intéressant, tout comme une prévision infrajournalière à pas de temps de 6 h.

Finalement, nous avons introduit une technique d’optimisation globale, les algorithmes génétiques, capable de calibrer la méthode des analogues en considérant tous les paramètres des différents niveaux d’analogie de manière conjointe. Avec cette technique, nous pouvons nous approcher objectivement d’une paramétrisation optimale. Le choix des niveaux atmosphériques et des fenêtres temporelles et spatiales étant automatisé, cette technique peut engendrer un gain de temps, même si elle est relativement exigeante en calculs. Nous avons ainsi pu améliorer la méthode des analogues, et y ajouter de nouveaux degrés de liberté, notamment des fenêtres spatiales et des pondérations différenciées selon les niveaux atmosphériques retenus.