Abstract:
Large wave events have been observed in the Viaduct Marina. It is believed that, as well as wind generated ocean waves, high speed ferries operating locally are contributing to these unfavourable conditions. In order to assess the sea state inside the Viaduct Marina during propagation of ferry wakes and wind waves into the marina, analysis of various locations inside and offshore from the marina was undertaken. Two methods of analysis were used in this study, a field monitoring study (using the doppler/pressure based Nortek Aquadopp Current Meters) and a computational modelling study (using Mike21 by DHI). The data recorded during the field monitoring study was used to assess ferry wakes and wind waves generated by a storm event. The computational modelling study assessed the sea state inside the marina resulting from various different wind speeds and directions. Analysis of the field monitoring study data showed that incident ferry wakes had a period of 4 to 6 seconds and a significant wave height of ranging from 0.2-0.25 metres. The wind generated waves had significant periods ranging from 2.3 to 3.1 seconds and significant wave heights ranging from 0.1-0.33 metres. The marina walls were effective at reducing incident wave heights by 61-76% during wave propagation into the marina. Spectral analysis of the field monitoring study data showed that the wind generated waves had a broader energy distribution than ferry wakes. The computational modelling study concluded that the Viaduct Marina experiences the most adverse sea state when the wind direction is blowing from between north-east to east. Wind wave events resulting in a high sea state were shown to occur inside the marina when the wind speed was 20 metres per second and blew from a north-east to easterly direction.