Action 3A: Trans-national coastal flood risk assessment:
probing a uniform method

In this study a global flood risk assessment for the North Sea basin is presented. An important objective within this project is to share information and develop a trans-national perspective on flood risk management for the whole North Sea area. Starting point of this study is the current situation (2007) as a reference, from where future developments (climatic and socio-economic) until 2050 are reflected. The failure of flood defences were incorporated by the use of fragility curves. The outcomes of this study could be used to benchmark ideas and strategies in order to secure the region from flooding, now and in the future. Furthermore, this study may contribute to raised awareness on flood risk amongst flood prone societies in the North Sea basin and may serve as a reference framework for the implementation process of the EU Floods directive (2007).

► Final report (2008)  



             North Sea flood plains (pdf) and corresponding regions (see below)

► Annexes

► Flood risk maps 2007 / 2050:

  Map A: Humber estuary
  Map B: The Wash
  Map C: Thames Estuary
  Map D: Flanders
  Map E: Zeeland
  Map F: Central Holland
  Map G: Groningen-Fryslan
  Map H: Emden-Wilhelmshaven
  Map I: Wilhelmshaven-Bremen
  Map J: Hamburg
  Map K: Schleswig-Holstein


Special thanks are directed to our international partners in project Safecoast project who contributed to the contents of this report.
We hope that this report will contribute to general awareness on coastal flood risks and thinking about integrated coastal zone management. We are aware that this study is only a first attempt at a North Sea wide flood risk assessment and hope it will serve as a starting point for more elaborate risk assessments. Responsible partner for this action is Rijkswaterstaat - Centre for Water Management in co-operation with Deltares and executed by Oranjewoud BV.

Action 3B: The Flanders case study and transnational comparisons of different coastal flood risk methodologies

► Final report (2008) (20 mb)

In Safecoast Action 3B, a case study was executed for the flood prone area on the Flemish coast between Zeebrugge and the Dutch border (the coastal community of Knokke-Heist). This area includes the Flemish part of the case study ‘Vlaanderen / Zeeuwsch-Vlaanderen’ which was considered earlier in the Comrisk study (see downloads section). In this Safecoast Action, the hydraulic modelling part together with the damage and casualty calculations (including an extensive sensitivity analysis) were further elaborated using the methodological improvements developed in Safecoast.

Flood simulations were carried out with the commercially available model MIKE FLOOD which is a dynamically linked 1D and 2D flood modelling package, including a module for breach development. The failures of the flood defence systems were simulated within MIKE FLOOD based on certain assumptions on breach development and maximum breach width. The 2D flood model was based on the elevation model used in Comrisk. The basis for the damage calculations was derived form land use classes taken from Corine Land Cover 2000.

The flood risk assessments were based on assumptions of dike (or dune) breach locations. A total of 8 potential breach locations were assumed based on the relative weak spots in the flood protection system. An extensive sensitivity analysis of the hydraulic modelling was carried out; involving a large number flood simulations and damage assessments. The sensitivity analysis considered a range of different assumptions within the various modelling steps, among other including:

• time of breaching;
• horizontal and vertical breach growth rate;
• roughness in 2D flood modelling;
• resolution of elevation model and representation of linear structures;
• storm surge levels.

Flood simulations and damage assessments were made for different return periods, i.e. the 4,000; 10,000 and 40,000 year events.



From the simulation results it was concluded that the time of breaching and breach growth strongly influence damage risk and casualty risk. The most important parameter is the number of breaches and its location. For given breach locations, dimensions and timing, the most influential parameter in the flood model is the surface roughness. Moreover, the resolution of the elevation model and the presence of linear structures can strongly influence the results of a risk evaluation. The relative importance of these factors depends on the type of risk (damage or casualties).  Finally it is noted that in the risk analysis, the uncertainty on hydraulic boundary conditions and failure behaviour (see overview below) of the flood defences is dominant to the uncertainties related to flood modelling and damage assessments

Responsible partner for this action is Flanders Hydraulic Research [B]

 

 Examples of flood defence failure mechanisms for both hard defences (dikes, dams) and soft defences (dunes) Source: project VNK / Floris