Coastal flood: from modelling to risk assessment and mitigation

The environmental context in which human settlements and strategic infrastructures are found is inherently vulnerable to natural processes. Under specific conditions, these processes can significantly impact and potentially damage the territory and its various destinations of use. Therefore the general concept of natural hazard must be delineated considering the exposed and consequently vulnerable elements to be functional in the framework of geological risk assessment. In the last decades, the approach to natural hazard assessment has evolved to encompass not only the spatial and temporal probability of occurrence of natural processes but rather their potential effectiveness in impacting anthropic activities and territories. From the theoretical concept of hazard, which is distributed in space and assessed within specific time windows, the ‘scenario of effect’ has emerged as a crucial tool providing a more functional and straightforward forecasting basis for risk assessment. This analytical improvement derives from the ability of scenarios to explicitly reference the spatial extent of instabilities, also providing descriptive metrics of their occurring intensity. However, it is only in the last decade that scenario analyses have been refined to encompass the combined study of instability processes by considering their different spatial and temporal relationships, as well as the induced effects. This approach is based on the generalisation of a multihazard framework deriving from the consideration of induced effects that can be independent or interconnected. The multihazard perspective more accurately reflects the complex interactions and cumulative impacts of natural processes on the exposed territory, thus better aligning with a multirisk assessment approach. For the definition of these scenarios, the investigation of the predisposing factors (i.e. inherited from the local geological and geomorphological setting) to specific natural instabilities markedly improves the identification of those conditions that can progressively lead them towards different effect scenarios, hence featuring different probabilities of occurrence. Among those factors constraining the temporal variation in predisposing conditions, the climate and its variations play a significant role, as also witnessed by geological records and forward projections. The quantification of induced effects can ultimately be achieved through quantitative models of cause effect relationships, which require identifying triggering actions and evaluating their effectiveness. These actions typically occur over significantly shorter time intervals xi than environmental variations, such as those related to climate change, and are generally attributed to impulsive and paroxysmal processes (i.e. earthquakes, storms and volcanic eruptions). Nowadays, the progressive transition from hazard to scenario analysis engages a broad technical-scientific community, encompassing expertise in engineering geology to geomorphology, geophysics and geotechnics. A multidisciplinary approach is indeed essential for quantifying the effects induced by complex and often interconnected processes. The extensive scientific literature dealing with hazard analysis provides an opportunity to establish logical-operational workflows by encompassing methodologies developed for various processes and contexts, and synthesised through applied, tested and validated case studies. These workflows can ensure the definition of quantitative induced-effect scenarios for a wide range of processes and environments. The thorough investigation and rationalisation of data, particularly from literature sources, can be considered a repository of learning cases, hence representing the foundation for the development of specific tools for the analysis and delivery of effect scenarios. These learning cases can yield multiple analytical tools whose integration can strongly contribute to the quantification of effect scenarios in a multihazard perspective. In other words, this approach would benefit from adopting a methodology able to transition from retrospective back analysis to the generalisation of operational tools, under specific constraints, aiming at the predictive formulation of scenario effects for forward analysis. This approach is definitively more functional for analysing the combined risk deriving from multihazard, as it integrates information levels related to the exposed anthropic systems and surrounding environment, the latter of which is considered as a complex system of geo-, bio-, anthropogenic interconnections. This book aims to provide an overview of different geological processes potentially causing risk conditions by providing an exhaustive state-of-the-art as well as examples of quantitative risk analysis and assessment with the final goal of creating effective scenario analysis. The introductory chapter provides basic definitions, focuses on multihazard and multirisk approaches, then delves into the role of communities in implementing effective risk reduction actions and, finally, dwells on and deepens the concept of resilience. The following chapters deal more in depth with the different types of natural geological and geomorphological processes in a scenario effect perspective. In this regard, natural processes related to ground instability, earthquakes, floods in coastal areas and fall of volcanic materials over large areas were selected for a more detailed description. Internationally renowned researchers, in coauthorship with younger researchers, contributed to these chapters to outline the relevance of the ongoing transition that the scientific community dealing with these research topics has been experiencing in the last decade. xii Preface The research topics covered in this book represent to date a frontier as well as the core of international projects, including those financed in Europe by the Recovery and Resilience Plan funded by the European Community with the Next-Generation European Community Program. Our hope for readers is to grasp the transitory and, as such, continuously evolving nature of the approaches discussed in this volume. Our editorial effort consisted in reproducing in this volume some scenes from a film that is still on screens and whose epilogue has yet to be shown.