Flood modeling for risk evaluation: a MIKE FLOOD sensitivity analysis

The flood risk for a section of the Belgian coastal plain was evaluated by means of dynamically linked 1D (breach) and 2D (floodplain) hydraulic models. First, a one-at-a-time factor screening was performed to evaluate the relative importance of various model processes and parameters. Subsequently, a systematic sensitivity analysis was added to establish the contribution of the most influential factors (breach growth and surface roughness) to hydraulic modeling uncertainty. Finally, the uncertainty associated with hydraulic modeling was compared to the uncertainty associated with coastal defense failure analysis. The former was found to be considerable, but nevertheless small compared to the latter

The impact of individual buildings on urban flood risk analysis

When performing an urban flood risk analysis, it is often difficult to take individual buildings into account: doing so requires the availability of a high resolution 2D hydrodynamic model for the preparation of flood maps and detailed land use maps for the preparation of flood damage maps. As a consequence, a simplified approach is often required, involving the use of low resolution models and simplified land use maps. This study aims at evaluating the impact of such simplifications on the flood risk by means of a case study: the flooding of the city of Antwerp (Belgium) caused by wave overtopping of the flood defenses along the river Scheldt. Two methods for computing flood maps were combined with two methods for computing damage maps, yielding four different methods for computing urban flood risk. The results obtained with the four methods differ significantly. The flood risk predicted by a combination of the detailed approaches was found to be less than 30% of the flood risk predicted by a combination of the simplified approaches. From this study, we can conclude that the procedures used for dealing with the presence of buildings can be a significant source of uncertainty in urban flood risk analysis

SAFECoast: Comparison between different flood risk methodologies. Action 3B report - SAFECOAST Interreg IIIb North Sea Project

The Interreg IIIB project SAFECoast considers the question “How to manage our North Sea coasts in 2050?’ and focuses on the consequences of climate change and spatial developments with respect to safety from coastal flooding. Therefore, a team of coastal managers from the Netherlands, Germany, Belgium, Denmark and the UK are continuing their cooperation in SAFECoast which aims to build on each other’s experiences in, and understanding of coastal risk management. Flanders Hydraulics Research (FHR, located in Borgerhout, Belgium) has proposed a flood risk methodology in the past which makes it possible to compare different areas and different situations with a view to damage and risk calculations. In the past years, the methodology has been extended and improved, and meanwhile it is used in several studies in Flanders. This report is the contribution of Flanders Hydraulics Research to the SAFECoast project (action 3b). The goal is to compare basic parameters of the existing coastal risk methodologies and make an inventory of the strong and weak points of the different approaches. It is neither possible nor desirable to make a ranking of them. Because of data availability and case specific parameters and constraints, each methodology generally fits the best for the area they are made for. However we want to learn from them and incorporate good ideas to improve the existing methodologies. To improve coastal risk methodology means to make its results less uncertain, or more complete. In this study all the different sources of uncertainty are analysed and compared so it becomes possible to identify the weak links in the calculation chain

Assessing the storm vulnerability of the Belgian coastline

Climate change is likely to induce increased sea level and storm frequency. As such, assessing the strength of the Belgian coastal defence infrastructure against natural hazards is of primordial importance to reduce inundation consequences to properties and nature. This study presents an integrated methodology to estimate damage risks from a hypothetical storm with a surge level of +8m TAW and a duration of 45 hours along the entire coastline. After translation of deep water hydrometeorological conditions to the nearshore, several failure modes of the defence infrastructure are modelled: beach and dune erasion, collapse of dikes due to wave impact and overtopping, and subsequent breach forming and flooding of the low-lying coastal plain. Attention was paid to the various model uncertainties. Damage of infrastructure, properties and human casualties are calculated using a raster-based GIS model. Multiplication of the results with a rate factor based on prognoses of the evolution of socio-economic parameters allows projection of the results to 2050. All this, in combination with a social cost benefit analysis, will provide a tool for supporting coastal zone management in Belgium in a quantitative way

Coastal flooding risk calculations for the Belgian coast

Coastal flooding risk calculations are carried out for the entire Belgian coastal zone to support the management ofthe coastal defence system. The floodprone low-lying coastal area has an average width of 20 km and is locatedon average 2 m below the surge level of an annual storm. The natural sea defences are sandy beaches anddunes, which have been strengthened by revetments in the coastal towns. The Belgian standard of coastalprotection is to be safe against a surge level with a return period of 1000 years, but at present it is investigated if and how this standard could be redefined based on risk analysis

Optimization of 2D flood models by semi-automated incorporation of flood diverting landscape elements

A simple GIS procedure was used for restoring narrow linear flood diverting landscape elements in rectangular grid digital elevation models. Subsequently, four different DEM’s (fine and coarse grid, with and without linear elements) were incorporated in 2D flood models. Finally, the various flood models were used to compute flood risk in the eastern part of the Belgian coastal plain. The results obtained with fine and coarse grids were quite different, but when linear elements were restored in both grids, they agreed remarkably well. The application of this GIS procedure allows model run times to be reduced by an order of magnitude, while still preserving flood risk accuracy