Quantifying the risk to life posed by hyperconcetrated flows

2012-2013In recent years, the disasters caused by landslides tragically increased due to the demographic growth and the indiscriminate use of land. Among the different types of landslides, flow-like phenomena - often simultaneously affecting large areas - are associated with the most catastrophic consequences in terms of loss of human life and economic damage. Understanding, forecasting and controlling the risk posed by flow-like phenomena are now recognised to be a priority for the safety of human life. As a result, a growing interest of both technical and scientific Communities, in performing risk analyses aimed at estimating the risk in a quantitative way has been recorded (Corominas et al., 2013). This PhD Thesis focus on the use of the quantitative risk analysis (QRA) procedures, specifically aimed at estimating the risk to life posed by flow-like phenomena. The use of QRA can allow the overcoming of some limits inherent to qualitative risk analyses in addressing practical problems (i.e. the prioritisation of management and mitigation actions as well as the allocation of associated resources). However, mainly theoretical contributions are provided on the topic at the international level. This can be due to the complexity of the procedures to be adopted for QRA purposes as well as to the significant amount of required input data (of both technical and socio-economic nature). The main goal of this research is to fill this gap by applying, improving and optimising the use of the QRA as a formal and structured tool for professionals involved in the management of the risk posed by flow-like phenomena. In this regard, the research activities focus on the quantitative estimation of the risk for loss of life, at medium and site-specific scale, posed by the occurrence of hyperconcentrated flows. The Thesis preliminarily provides a description of the main features of the flow-like phenomena, with an emphasis to those dealing with debris flows and hyperconcentrated flows. Then, the basic concepts and methodological approaches (with their limits and potentialities) of both qualitative and quantitative risk analysis and zoning are discussed. An overview of the current risk zoning in Italy, performed via qualitative risk analyses, is thus presented. On the basis of the above premises, the relevant benefits that, at regional and at site-specific scales, can be achieved passing from a qualitative to a quantitative risk analysis are highlighted. At medium scale, the analysis of historical records of landslide events in the Campania region (southern Italy) allows the identification and the characterisation of the different flow-like phenomena that may occur. In particular, these latter are individuated within a homogeneous geological context where carbonate slopes are covered by pyroclastic soils systematically affected by rainfall-induced slope instabilities later propagating as – often catastrophic in terms of life and properties losses – debris flows or hyperconcentrated flows. The thorough studies and researches carried out as well as the original results achieved allow to make relevant considerations – from both technical and scientific points of view – concerning both their spatial and temporal distribution (in terms of frequency) and the initial and boundary conditions which influence their occurrence. At detailed scale, the research activity focus on the quantitative estimate of the risk to life loss with reference to residents at the toe of Monte Albino (located in the Municipality of Nocera Inferiore (SA), Campania region), posed by the occurrence hyperconcentrated flows. The novelty of the proposed procedure consists in conjugating the fundaments of the risk theory with the geotechnical approach, providing a deeper understanding of the mechanisms that leads to the different and complex stages of movement. To this aim, a thorough in-situ investigations (with the purpose of framing the geological and geomorphological characteristics and to identify the 'hillslope' proneness to different slope instabilities, to characterise the spatial distribution of soil pyroclastic covers and their litho-stratigraphic structure) and laboratory tests (in order to have a complete physical and mechanical characterisation of the involved soils) are carried out. This study represents the indispensable prerequisite for the correct engineering modelling of phenomena at detailed scale - from the triggering stage to the propagation stage - obtaining in this way the definition of different hazard scenarios. The obtained results are used to estimate the expected consequences in terms of loss of human life with reference both to the most exposed persons within each of the impacted houses (to which corresponds the highest temporal-spatial probability) and to the average exposed person in open space (representing the average behaviour of a group of people). Finally, the procedure of quantitative risk estimate has allow to rank the portions of the urbanised territory at risk and, consequently, to provide a prioritisation of the areas needing structural mitigation measures. [edited by author]XII n.s

Landslide analysis and early warning

In jüngerer Vergangenheit aufgetretene gravitative Massenbewegungen verdeutlichen die Notwendigkeit die Vorhersagemöglichkeiten von und die Frühwarnung vor gravitativen Massenbewegungen zu verbessern, um die damit verbundenen Risiken zu reduzieren und Menschenleben zu schützen. Die vorliegende Arbeit beschäftigt sich mit lokalen und regionalen Analysen der auslösenden Bedingungen gravitativer Massenbewegungen an der Schwäbischen Alb, und der Entwicklung von Frühwarnsystem Prototypen. Im lokalen Untersuchungsgebiet wurde ein extensives hydrologisches und Hangbewegungsmonitoringsystem auf einem saisonal reaktivierten Hangrutschungskörper in Lichtenstein-Unterhausen installiert. Basierend auf der Analyse von Monitoringdaten wurde der Einfluss von Niederschlag und Schneeschmelze auf die Grundwasserbedingungen und die Initiierung von Hangbewegungen untersucht. Das kombinierte Hydrologie und Stabilitätsmodell CHASM wurde verwendet, um Hangbereiche auszuweisen, für die ein Versagen wahrscheinlich ist, und die Auswirkungen einer Vielzahl von Einflussfaktoren auf die Hangstabilität zu simulieren. Auf den Ergebnissen aufbauend wurden zwei Internet-basierte Anwendungen entwickelt. Die erste Applikation stellt ein technisches Frühwarnsystem dar, in dem die Hangstabilität unter Verwendung von gemessenem Niederschlag, hydrologischen Monitoringdaten und Wettervorhersagen fortlaufend simuliert wird. Die zweite Anwendung dient der Entscheidungsunterstützung und erlaubt eine schnelle Berechnung der Hangstabilität für frei wählbare Profile. Auf der regionalen Ebene wurden verfügbare Inventare gravitativer Massenbewegungen analysiert und hinsichtlich einer Bewertung von Niederschlagsschwellenwerte anderer Studien ausgewertet. Adäquate gravitative Massenbewegungen wurden ausgewählt und deren auslösende Niederschlags- und Schneeschmelzekonditionen mit Intensität-Dauer und kumulativen Schwellenwerten verglichen. Aufbauend auf den Ergebnissen wurde ein regionales Frühwarnsystem für gravitative Massenbewegungen entwickelt und als Internet-basiertes Anwendung implementiert. Die entwickelten lokalen und regionalen Frühwarnsysteme sind Teil einer holistischen und integrativen Frühwarnkette, welche durch das ILEWS Project implementiert wurde, und können auch auf andere von gravitativen Massenbewegungen betroffene Gebiete übertragen werden.Recent landslide events demonstrate the need to improve landslide forecasting and early warning capabilities in order to reduce related risks and protect human lives. In this thesis, local and regional investigations were carried out to analyse landslide characteristics in the Swabian Alb region, and to develop prototypic landslide early warning systems. In the local study area, an extensive hydrological and slope movement monitoring system was installed on a seasonally reactivated landslide body located in Lichtenstein-Unterhausen. Monitoring data was analysed to assess the influence of rainfall and snow-melt on groundwater conditions, and the initiation of slope movements. The coupled hydrology-slope stability model CHASM was applied to detect areas most prone to slope failures, and to simulate slope stability using a variety of input data. Subsequently, CHASM was refined and two web-based applications were developed: a technical early warning system to constantly simulate slope stability integrating rainfall measurements, hydrological monitoring data and weather forecasts; and a decision-support system allowing for quick calculation of stability for freely selectable slope profiles. On the regional scale, available landslide inventory data were analysed for their use in evaluation of rainfall thresholds proposed in other studies. Adequate landslide events were selected and their triggering rainfall and snow-melting conditions were compared to intensity-duration and cumulative thresholds. Based on the results, a regional landslide early warning system was developed and implemented as a web-based application. Both, the local and the regional landslide early warning systems are part of a holistic and integrative early warning chain developed by the ILEWS project, and could easily be transferred to other landslide prone areas

Flood Risk and Resilience

Flooding is widely recognized as a global threat, due to the extent and magnitude of damage it causes around the world each year. Reducing flood risk and improving flood resilience are two closely related aspects of flood management. This book presents the latest advances in flood risk and resilience management on the following themes: hazard and risk analysis, flood behaviour analysis, assessment frameworks and metrics and intervention strategies. It can help the reader to understand the current challenges in flood management and the development of sustainable flood management interventions to reduce the social, economic and environmental consequences from flooding

The SLIP model: A major step towards the application in real time civil protection integrated platforms for landslide prevention.

This work has focused on validating, on a large scale, the physically based model, named SLIP (Shallow Landslide Instability Prediction) for its future application in real time civil protection integrated platforms, after almost 15 years from its first formulation. Many works have been carried out by our research group using this model to back analyze occurred events and with the correct calibration of its input data the model always gave good results. In this thesis a further validation on various aspects of the model have been carried out from the prediction of instability of simulated landslides in laboratory flume tests to a real scale analysis. Particularly SLIP has been used to model two case studies, namely the landslide event that hit the Parma Apennines in April 2013 and the event of Giampilieri (ME) occurred the 1st October of 2009. In the first study case a large gathering of information was carried out from both in situ measurements and laboratory tests on the landslides and its soil. Thanks to an already known background for this type of soil, studied in previous works of our research group, the modeling gave good predictive capability. A new technique that extracted spatial land cover classes from pre-event flight images was consequently used. There was a clear improvement in the overall accuracy of the model between the cases in which this differentiation was used and not showing how a better spatial variation of parameters can improve the model predictive capacity. From a temporal stand point both the parameter sets give excellent results remarking the instability pattern that witnesses and local news provided. The results highlight a good prediction although there is a high over prediction ratio in the first set, and some false alerts in the second set. These problems can be related to an incomplete landslide database and spatial errors due to the absence of post event images. The calibration of the input parameters of the Giampilieri event was made by laboratory geotechnical characterization, numerical models for hydraulic parameters and by simulating in a small scale flume the triggering of landslides. Flume tests can be used for multiple purposes, such as to evaluate in back-analysis the initial soil conditions of a reference landslide event, but also to define several input parameters of SLIP model, as well as to analyze in detail the triggering mechanisms of the material potentially susceptible to shallow landslides. Furthermore, the apparatus used in this study is not complex or expensive. With the correct expedients, such as insertion of macro channels, the flume can be used to simulate the real case and to model hypothetical scenarios before they occur in real slopes. The outcome of flume tests underlines the influence of initial soil conditions on times and modalities of slope failure, as well as indicating how a variable rainfall input produces an increase of water infiltration compared to a constant one of same cumulative depth. The output of two models, SLIP and TRIGRS, a well established model, are shown. The results indicate that the models reconstruct quite well the event, both in terms of temporal evolution and spatial distribution of slope instability, and identify substantially the same areas mostly affected by shallow landslides. The comparison confirms the good predictive capability of the SLIP physically-based model, considering that the two maps converge to the same solution in large part of the study area, although SLIP overestimates spatially the instability while TRIGRS underestimates the landslide occurrence and slightly overestimates temporally the duration of the landslide event. SLIP is a more simple model than TRIGRS requiring less input parameters. The results of a two-year daily analysis are shown only using the SLIP model because a yearly analysis with TRIGRS would require elevated computational time. The results show haw the model well predicts instability capturing both the reported events of this time span and producing only one false alert. SLIP model returns the results in a few minutes for large areas. This means that updated triggering scenario maps can be obtained substantially in real-time. This feature is obviously essential considering a possible integration of the approach with an early warning system. Furthermore, if SLIP model was used in this way, it would operate with rainfall inputs forecasted for the next hours, then much more reliable than those estimated with a statistical analysis of historical rainfall data which, furthermore, are not always available for a specific area. Overall, if coupled with forecasted rainfall maps the model could be used as a preliminary early warning system for landslides and could be used to simulate landslide susceptibility over large areas with different rainfall scenarios

Global Risk Assessment of Natural Disasters: new perspectives

Natural disasters such as earthquakes, tsunamis, landslides and volcanic activities has had devastating effects on human life. Risk is the probability of harmful consequences from the interaction of hazards and vulnerable conditions. With increasing numbers of people living in crowded cities and other vulnerable areas, it is more important than ever to advance our understanding of natural disasters and the ways in which humans respond to them. My interdisciplinary study reflected in my thesis includes integrated research on the risk assessment methods for natural hazards with focus on earthquake disasters. This thesis address firstly the development of a scaled risk assessment framework, comparative assessment of natural hazard losses, including respective case studies and global overview of natural hazard risk, and secondly a comparative risk assessment of geological disasters to elaborate the major disastrous hazards for global population. Furthermore, I evaluate the effect of past events in form of the number of losses with respect to the exposed population on the proneness of people to the disaster. I summarize acceptable risk criteria and the necessity of having a normalized framework for societal risk assessment. I evaluate the natural hazard risk assessment and acceptable risk criteria of 32 European countries. I also introduce the concept of resistance in both risk equation and in FN-curves. Resistance is the societal resilience of a society to the occurrence of a natural disaster. Moreover, using components of FN-curves (slopes and intercepts) for risk assessment of geological disasters based on real data, I showed that the world has been more at risk of earthquakes than tsunamis, volcanic activities and landslides since 1600. Also. based on the earthquake disasters data (1973-2010), I evaluated the temporal trend of hazard, risk, exposure and resistance of the world towards earthquake disasters. Our results does not provide any evidence of increase or decrease in the temporal trend of fatality rate and earthquake resistance while there is a significant decrease in the crude death rate. Finally, we evaluated the reliability of earthquake disaster system during 1950-2012 using probability of more than 1000 fatalities as probability of failure. Our yearly estimate of reliability at the beginning of each mission year shows that the avreage reliability of earthquake disaster system is very low (~0.3) and it is decreasing over time, too.4 month

Proceedings of the 9th Annual International Conference of the International Institute for Infrastructure Renewal and Reconstruction

Proceedings of The 9th Annual International Conference of the International Institute for Infrastructure Renewal and Reconstruction. The conference was held at Queensland University of Technology (QUT), Brisbane, Australia from 8-10 July 2013. The event title for the 9th Annual Conference was: Risk-informed Disaster Management: Planning for Response, Recovery and Resilience. All papers were double blind peer reviewed and the Proceedings were published online in March 2015

From Regional Landslide Detection to Site-Specific Slope Deformation Monitoring and Modelling Based on Active Remote Sensors

Landslide processes can have direct and indirect consequences affecting human lives and activities. In order to improve landslide risk management procedures, this PhD thesis aims to investigate capabilities of active LiDAR and RaDAR sensors for landslides detection and characterization at regional scales, spatial risk assessment over large areas and slope instabilities monitoring and modelling at site-specific scales. At regional scales, we first demonstrated recent boat-based mobile LiDAR capabilities to model topography of the Normand coastal cliffs. By comparing annual acquisitions, we validated as well our approach to detect surface changes and thus map rock collapses, landslides and toe erosions affecting the shoreline at a county scale. Then, we applied a spaceborne InSAR approach to detect large slope instabilities in Argentina. Based on both phase and amplitude RaDAR signals, we extracted decisive information to detect, characterize and monitor two unknown extremely slow landslides, and to quantify water level variations of an involved close dam reservoir. Finally, advanced investigations on fragmental rockfall risk assessment were conducted along roads of the Val de Bagnes, by improving approaches of the Slope Angle Distribution and the FlowR software. Therefore, both rock-mass-failure susceptibilities and relative frequencies of block propagations were assessed and rockfall hazard and risk maps could be established at the valley scale. At slope-specific scales, in the Swiss Alps, we first integrated ground-based InSAR and terrestrial LiDAR acquisitions to map, monitor and model the Perraire rock slope deformation. By interpreting both methods individually and originally integrated as well, we therefore delimited the rockslide borders, computed volumes and highlighted non-uniform translational displacements along a wedge failure surface. Finally, we studied specific requirements and practical issues experimented on early warning systems of some of the most studied landslides worldwide. As a result, we highlighted valuable key recommendations to design new reliable systems; in addition, we also underlined conceptual issues that must be solved to improve current procedures. To sum up, the diversity of experimented situations brought an extensive experience that revealed the potential and limitations of both methods and highlighted as well the necessity of their complementary and integrated uses