Reliability analysis and breach modelling of flood defences in an integrated risk analysis—results of the XtremRisK project

Coastal Engineering Journal

Burzel

et al. 2015

Coast. Eng. J. 2015.57. Downloaded from www.worldscientific.com by UNIVERSITY OF CALIFORNIA @ SAN DIEGO on 06/03/15. For personal use only. H. Oumeraci et al.A brief overview of the joint research project XtremRisK is given. The project has been focusing on developing/improving/expanding the knowledge, methods and models with respect to (i) physically possible extreme storm surge for current conditions and scenarios for climate change, (ii) failure mechanisms of flood defenses, (iii) assessment of intangible losses (social and ecological) and their integration with direct/indirect economic losses, (iv) reliability analysis of flood defense systems and (v) sourcepathway-receptor (SPR)-based integrated flood risk analysis involving both tangible and intangible losses and its implementation for two selected pilot sites (representative for an open coast and an urban estuarine area in Germany). The key results are briefly summarized and the lessons learned for future flood risk studies are finally drawn.

Section: Key Resultsmentioning

confidence: 99%

XtremRisK — Integrated Flood Risk Analysis for Extreme Storm Surges at Open Coasts and in Estuaries: Methodology, Key Results and Lessons Learned

Coastal Engineering Journal

Burzel

et al. 2015

“…For the reliability analysis the following main steps were performed: (a) identification of flood defense segments in the aforementioned areas; (b) identification of relevant [Naulin et al, 2012]. failure mechanisms and LSEs for each of these segments; (c) failure probability calculations; (d) combination of the different failure mechanisms by a fault tree analysis to calculate the flooding probability for a single flood defense element and the entire flood defense system.…”

Section: Reliability Analysismentioning

confidence: 99%

“…9. Time-dependent processes of resistance and loading for different time scales: (a) short term; (b) mid term and (c) long term [Naulin et al, 2012].…”

Section: Time Dependencymentioning

confidence: 99%

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Reliability-Based Flood Defense Analysis in an Integrated Risk Assessment

Naulin

Coastal Engineering Journal

2015

Failures of flood defenses have been one of the major reasons in the past leading to flooding of the hinterland behind flood defenses along rivers and at the sea. It is therefore inevitable to investigate the reliability of such defenses for extreme events as have occurred in the past and are discussed to happen more frequently in the future and due to climate changes. The first subproject in XtremRisK (SP 1) and the related papers in this issue "A multi-method approach to develop extreme storm surge events to strengthen the resilience of highly vulnerable coastal areas," Coast. Eng. J., this special issue; Wahl, T. et al. [2015] "Statistical assessment of storm surge scenarios within integrated risk analyses," Coast. Eng. J., this special issue; Tayel, M. and Oumeraci, H.[2015] "A hybrid approach using hydrodynamic modelling and artificial neural networks for extreme storm surge prediction, Coast. Eng. J., this special issue] have investigated the components of storm surges and their statistical occurrence, also in relation to the wave parameters. These results can now be used as input for investigating the reliability of flood defenses and provide an overall failure probability for different types of defenses and different failure modes. This paper therefore summarizes the key findings of the "risk pathway" analysis of XtremRisK Subproject 2 (SP 2) which comprise a reliability analysis 1540005-1 M. Naulin, A. Kortenhaus & H. Oumeraciand breach modeling of coastal and estuarine flood defenses using storm surge scenarios and sea states, including their occurrence probabilities provided by XtremRisK SP 1. The paper discusses the key results, the progress, and challenges in reliability analysis and breach modeling of flood defenses. The developed and advanced methods were applied to pilot sites in Hamburg (Elbe Estuary) and the Island of Sylt (North Sea). These pilot sites are mainly protected by linear flood defenses such as sea dikes, estuarine dikes, coastal dunes, and flood defense walls. Results have shown that under extreme conditions many dikes may fail simply from wave overtopping and even overflow but also from dike breaching due to the severe loading of the dike slopes when heavy overtopping and overflow occurs. The inflowing water volumes were calculated based on time-dependent water levels and then used for inundation modeling of the hinterland in Subproject 3 (SP 3) of XtremRisK. Furthermore, the limit state equations for wave overtopping and overflow had been adapted to time-dependent simulations. An importance factor was introduced for the probability of breaching of sea dikes leading to significantly different failure probabilities. The length effect considering the different homogeneous segments in the dike ring of Hamburg-Wilhelmsburg was estimated using an upper and lower bound approach showing the importance of the segmentation of the dike ring.

“…As for stochastic approaches Wahl et al (2012) not only used the maximum storm surge levels but widened the statistical analyses to the full history of individual storm surges (up to five tidal cycles) and proposed bivariate joint exceedance probabilities for peak water levels and the 'fullness' of these curves using Copula functions. Naulin et al (2012) discussed the reliability assessment of flood defences and more recent updates for failure modes and breach developments of dikes and dunes. The final outcome of this paper is a better understanding and description of different flood defences in two pilot sites in an estuary (Hamburg-Wilhelmsburg) and at the open North Sea (island of Sylt) where the overall failure probabilities of these flood defences were achieved for certain storm surge scenarios.…”

Section: Introductionmentioning

confidence: 99%

Flood Risk Assessments - Results, Applications and Future Requirements

Int. Conf. Coastal. Eng.

2014

This paper summarises and discusses the key results of two research projects one of which was a 4-year joint research project in Germany (XtremRisK) and the other comprised applications of the XtremRisK results to selected cases in Denmark (HARIMA-DK) within the framework of the European Flood Directive on the generation of hazard and risk maps for preselected areas. The former project focused on improving and expanding the existing knowledge, methods and models on flood risk assessments for extreme storm surges with respect to (a) extreme storm surge for current conditions and scenarios for climate change, (b) failure mechanisms of flood defences, (c) assessment of tangible and intangible losses, (d) integrated flood risk analysis involving the aforementioned developments and its implementation for two selected pilot sites (representative for an open coast and an urban estuarine area in Germany). The HARIMA-DK project used these results, applied it and produced flood risk maps for selected coastal areas in Denmark. The key results of both projects are briefly summarised, lessons learned are discussed and some conclusions for future flood risk studies are finally drawn.