Abstract
Understanding the role of beach morphology in controlling wave overtopping volume will further minimise uncertainties in flood risk assessments at coastal locations defended by engineered structures worldwide. XBeach is used to model wave overtopping volume for a 1:200 year joint probability distribution of waves and water levels with measured, pre- and post-storm beach profiles. The simulation with measured bathymetry is repeated with and without morphological evolution enabled during the modelled storm event. This research assesses the role of morphology in controlling wave overtopping volumes for hazardous events that meet the typical design level of coastal defence structures. Results show that disabling storm-driven morphology under-represents modelled wave overtopping volumes by up to 39% under high H s conditions and has a greater impact on the wave overtopping rate than the variability applied within the boundary conditions due to the range of wave-water level combinations that meet the 1:200 year joint probability criterion. Accounting for morphology in flood modelling is therefore critical for accurately predicting wave overtopping volumes and the resulting flood hazard and to assess economic losses.
Highlights
For storm events at and beyond the design level of modern, engineered flood defences, it is expected that the defence will experience partial wave overtopping or infiltration through the defence materials by high water levels
Our results clearly demonstrate that, under high Hs conditions, excluding morphology considerably under-estimates wave overtopping volume by up to 2959 m3 and 3010 m3 under Scenarios 1 and 2, 36% and 39% lower than the morphology-enabled wave overtopping volumes, respectively
We have demonstrated a method to use XBeach to determine the role of storm-driven changes in beach morphology under various joint probability Hs-water level (WL) combinations
Summary
For storm events at and beyond the design level of modern, engineered flood defences, it is expected that the defence will experience partial wave overtopping or infiltration through the defence materials by high water levels This may lead to breaching, which is the reduction of a defence’s effective crest height, where flood water propagates through gaps in the defences as a result of structural failure. Due to high flood velocity in the vicinity of breaches, there is an increase in the dangers associated with flooding, such as instability, drowning and impact from debris and building collapse [4] These additional risks were clear in the U.K. during the 1953 North Sea floods, when defences were breached in 1200 places [5]. These increased risks reinforce the need for effective flood risk assessment to account for risks of inundation from sea defence breaching
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