Browsing by Author "Salonen, Nicholas M"

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    Towards Rogue Wave Characterization in False Bay, South Africa
    (2019) Salonen, Nicholas M; Vichi, Marcello; Rautenbach, Christo
    Rogue waves are extreme oceanic waves which exceed twice the significant wave height of the wave record. In False Bay, South Africa, a shallow sea mount called rocky bank was suggested by Shipley (1964) to be the cause for increased wave energy along the eastern periphery of False Bay, where it is not uncommon for coastal users, particularly rock fishermen, to be washed off of the rocky coastline. The shallow bathymetry associated with rocky bank refracts the incoming open ocean swell and is thought to focus the wave energy toward sections of this coastline. This investigation aims to understand which offshore wave conditions could be conducive to rogue wave development along the eastern periphery of False Bay, South Africa. To do so, the phase-averaging spectral wave numerical model SWAN was used to investigate various wave conditions which are known to enter False Bay. The focusing effect which rocky bank supposedly has on the incoming wave energy was investigated by deepening and shallowing rocky bank's depth. This study showed that rocky bank does cause a varying degree of wave focusing which appears to be most dependent on the wave period, with higher wave periods leading to greater extents of refraction. According to this study, the average conditions which impact the south-western coastline of South Africa are conducive to wave focusing by rocky bank and despite the rarity of rogue wave events, coastal users are still affected by them. Calm seas have the ability to mislead users that make use of these dangerous rocky coasts, when the event of a rogue wave in small seas can still be sufficient to wash a person into the sea. A study by de Vos & Rautenbach (2019) suggested that users are at a higher risk, for a variety of coastal activities, during (seemingly) good conditions due to the increased human exposure. Since this study only simulated monochromatic wave conditions, one would expect the results to be significantly different if multiple swell systems were simulated concurrently, as this introduces the possibility of the dispersive focusing mechanism for swells that travel at different speeds and thus increasing the likelihood of a rogue wave. The knowledge acquired from this study is a great step towards understanding the wave climate of False Bay. This information can be used to implement possible warning systems which would hopefully be respected by the community and ultimately lessen the lives lost to extreme waves along False Bay's 'Death coast'.