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.

This paper estimates the economic costs from storm surge scenarios in the Free and Hanseatic City of Hamburg. Hydrodynamic and damage models simulate the direct damages to residential and commercial buildings and equipment in a part of the city named Hamburg-Wilhelmsburg. They are assigned to individual economic sectors and then integrated into an economic model. This model accounts for the indirect impacts due to the interruption of production processes. Furthermore, the indirect costs are allocated to the flooded and non-flooded area in the whole city of Hamburg and then to each firm according to its relative size. Thus, the spatial distribution of indirect damages can be visualized. The approach is a helpful tool to simulate potential total damages from storm surge scenarios at the city scale and can be used to assess the effectiveness of possible protection measures. The inclusion of indirect costs into flood risk mapping complements common risk mapping procedures.

Extreme storm surges have frequently led to major damages also along the German coastline. The joint research project 'XtremRisK' was initiated to improve the understanding of risk-related issues due to extreme storm surges and to quantify the flood risk for two pilot sites at the open coast and in an estuarine area under present and future climate scenarios. In this context, an integrated flood risk analysis is performed based on the source-pathway-receptor concept under consideration of possible tangible and intangible losses. This paper describes the structure of the project, the methodology of the subprojects, and first results. Moreover, integration approaches are discussed. The results of 'XtremRisK' will be used to propose flood risk mitigation measures for the prospective end-users.

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In consequence of the climate change, a sea level rise within the coming decades is highly probable and the intensity of storm surges will probably increase at least in the North Sea region. In this changing environment, great uncertainty exists about the need to adapt conventional coastal flood protection structures. This calls for response strategies to improve the flood resilience behind the dikes, in the Hinterland. Within this paper, the concept of cascading flood compartments is presented as an appropriate strategy to deal with the residual risk in the Hinterland. The key element of this approach is that an overtopping of the main dike line is accepted requiring their enforcement to resist erosion from hydrodynamic loads. Inner dikes are arranged in a multi-layer cascade of compartments creating a redundant system of flood containment. The necessary adaptations and restrictions to the built environment vary from simple resistance measures of dry-and wet-proofing to the development of amphibious settlements with floating homes and houses on piles. The whole concept is illustrated on the island of Wilhelmsburg in Hamburg, where urban areas are protected against storm surges through a ring dike. The necessary storage capacity of the flood compartment system is determined for the climate change scenarios of 2030 and 2085. A realistic arrangement of flood compartments can be found, proving the effectiveness and efficiency of this response strategy. 3d graphics illustrate the transfer from a water-abandoned city to an amphibious city, backing the statement that this flood response strategy opens new opportunities for cities.