Application of High Resolution Coupled Model to the Spatial Distribution Analysis of Coastal Total Water Level During Extreme Storm Events.

The interaction between tides, waves and surges has an impact on coastal total water level (TWL), which can rise to hazardous levels, possibly leading to floods. The environmental conditions related to the feedback processes between these variables dictate how the water level changes. The use of coupled numerical models allows more realistic reproduction of such processes and allows us to understand why some regions are impacted more heavily than others. Here, a new state-of-the-art high resolution regional coupled model developed at the UK MetOffice was applied to a case study, in order to better understand how the TWL and its components behaved at the UK and Irish coast during extreme storms. The spatial distribution of tides, residual surges and significant wave height was analyzed along the entire British and Irish coastlines during the extreme storms of the winter 2013-2014. Specific parameters dominate in certain regions: for example, the Bristol Channel and the English Channel were majorly impacted by the tides, while the signal on the west coast of Ireland was dominated by waves. The drivers are linked to interactions between oceanographic and atmospheric dynamics that are not fully understood. For example, coastal TWL can be affected by the impact the tidal stage has over surges or the influence of storm tracks, but it is not clear exactly what that impact is yet. The results show a way to improving our understanding and ability to predict TWLs during extreme events, with application to flood management and coastal protection.