Modelling elevations, inundation extent and hazard risk for extreme flood events

Climate change is expected to result in more frequent occurrences of extreme flood \nevents, such as flash flooding and large scale river flooding. Therefore, there is a \nneed for accurate flood risk assessment schemes in areas prone to extreme flooding. \nThis research study investigates what flood risk assessment tools and procedures \nshould be used for flood risk assessment in areas where the emergence of extreme \nflood events is possible. The first objective was to determine what type of flood \ninundation models should be used for predicting the flood elevations, velocities and \ninundation extent for extreme flood events. Therefore, there different flood \ninundation model structures were used to model a well-documented extreme flood \nevent. The obtained results suggest that it is necessary to incorporate shock-capturing \nalgorithms in the solution procedure when modelling extreme flood events, since \nthese algorithms prevent the formation of spurious oscillations and provide a more \nrealistic simulation of the flood levels. The second objective was to investigate the \nappropriateness of the “simplification strategy” (i.e. improving simulation results by \nincreasing roughness parameter) when used as a flood risk assessment modelling tool \nfor areas susceptible to extreme flooding. The obtained results suggest that applying \nsuch strategies can lead to significantly erroneous predictions of the peak water \nlevels and the inundation extent, and thus to inadequate flood protection design. The \nthird and final objective was to determine what type of flood hazard assessment \nmethods should be used for assessing the flood hazard to people caused by extreme \nflooding. Therefore, two different flood hazard assessment criteria were modelled for \nthree extreme flood events. The predicted results suggest that in areas prone to \nextreme flooding, the flood hazard indices should be predicted with physics-based \nformulae, as these methods consider all of the physical forces acting on a human \nbody in floodwaters, take into account the rapid changes in the flow regime, which \noften occur for extreme events, and enable a rapid assessment of the degree of flood \nhazard to be made in a short time period.