Flood risk analysis
An integrated risk analysis looks into both the probabilities and impacts of flooding. Modelling of river floods and/or storm surges forms an important part of the risk analysis.
Assessing flood probabilities
Flood disasters are rare. The challenge is to extrapolate from a limited set of observations to determine the probability of an extreme rainfall or discharge event. Various statistical techniques are available to perform such extrapolations. Our software package for hydrological data analysis HYMOS provides easy use of all the main distribution functions. Its application requires considering whether the results are physically realistic? Deltares has both the models and expertise to provide advice on sound extrapolations to assess flood probabilities.
Flood modelling of rivers
To translate an extreme event into a hydraulic load (a high water level) at the flood defence requires modelling of the runoff and of the river flow. For rivers SOBEK 1D/2D simulates the hydrodynamics of both the one-dimensional river/channel network and the two-dimensional overland flow. The model is suited to simulate the dynamic behaviour of overland flow over an initially dry land. It deals with every kind of geometry, including flat land or hilly terrain. The 1D channel network and the 2D rectangular grid hydrodynamics are solved simultaneously using the robust Delft scheme which is able to tackle steep fronts as well as sub critical and supercritical flow.
Storm-surge modelling for hurricanes and cyclones
In many semi-tropical coastal regions of the world, storms can turn into disastrous hurricanes or cyclones. For the last 10 years Deltares has been developing sophisticated storm surge modelling as part of early warning systems in various countries. For storm surge simulations with Delft3D-FLOW, a Wind Enhancement Scheme (WES) has been devised to generate a storm wind field. The program computes surface winds and pressure around the specified location of the moving eye of a cyclone taking into account the path or track of the storm. The WES model can use cyclone track data given by any Meteorological Agency.
Assessing flood impacts
There is always a risk of flooding from rivers or the sea, no matter how high and strong we make our embankments. What happens if a dike does fail? Simulations with our Sobek 1D/2D model assist in determining the extent and impacts of possible flood scenarios. The impacts include casualties as well as economic and environmental damage. Deltares performs casualty risk assessments using methods that combine the flood characteristics, such as water depth and flow velocity, with evacuation efficiency and vulnerability of inhabitants. A similar approach is adopted for economic damage, making use of damage functions for different types of land use (HIS-SSM).
Together with other research institutes and universities, Deltares is improving knowledge and tools that combine flood simulation models with damage functions and algorithms. Model results are being compared with empirical data from past disasters, such as Hurricane Katrina and the Elbe floods. The results are being used as input to a broad evaluation of the Dutch flood protection standards.
Software (downloads follow as soon as possible)
- DELFT-1D2D - simulation of natural flooding and inundation from dike and dam breaches.
- DELFT-3D – simulation of storm surges, tsunamis in oceans and coastal seas
- HIS-SSM - estimation of economic damage and casualties due to flooding (GIS-based)
- HYMOS – hydrological data analysis, including statistical analysis
