Modelling sea level surges in the Firth of Clyde, a fjordic embayment in south-west Scotland

Alessandro D Sabatino,Michael R Heath,Rory B O’Hara Murray,Douglas C Speirs,Alan Hills

doi:10.1007/s11069-016-2506-7

Alessandro D Sabatino, Michael R Heath + Show 3 more

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https://doi.org/10.1007/s11069-016-2506-7

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Abstract

Storm surges are an abnormal enhancement of the water level in response to weather perturbations. They have the capacity to cause damaging flooding of coastal regions, especially when they coincide with astronomical high spring tides. Some areas of the UK have suffered particularly damaging surge events, and the Firth of Clyde is a region with high risk due to its location and morphology. Here, we use a three-dimensional high spatial resolution hydrodynamic model to simulate the local bathymetric and morphological enhancement of surge in the Clyde, and disaggregate the effects of far-field atmospheric pressure distribution and local scale wind forcing of surges. A climatological analysis, based on 30 years of data from Millport tide gauges, is also discussed. The results suggest that floods are not only caused by extreme surge events, but also by the coupling of spring high tides with moderate surges. Water level is also enhanced by a funnelling effect due to the bathymetry and the morphology of fjordic sealochs and the River Clyde Estuary. In a world of rising sea level, studying the propagation and the climatology of surges and high water events is fundamental. In addition, high-resolution hydrodynamic models are essential to forecast extreme events and to prevent the loss of lives, or to plan coastal defences solutions.

Highlights

Storm surges are a tsunami-like sea level perturbation due to extreme low- or high-pressure weather systems, causing an enhancement or a decrease in the sea level at the coastline compared to the usual astronomical tides
Severe storm surges are rarely internally generated in the Clyde: This is the case of a low-pressure system moving from the North Atlantic Ocean to Ireland and to Clyde Sea itself
Our analysis of the historical tide gauge data showed that the highest water elevations in the Clyde Sea are recorded when spring high tides coincide with moderate to severe surge conditions, that from the statistical analysis in Fig. 7 usually occur during late autumn– winter

Summary

Introduction

Storm surges are a tsunami-like sea level perturbation due to extreme low- or high-pressure weather systems, causing an enhancement or a decrease in the sea level at the coastline compared to the usual astronomical tides. When this change is positive, surges threaten coastal communities, causing floods and damage to coastal infrastructures, and occasionally claiming the lives of people. This study is focused on the surges affecting some areas of the Clyde Sea, in the south-west of Scotland This area has been struck by several floods due to storm surges, since the well-documented massive surge of 1953 (Hickey 2001), such as the 5th January 1991 event that caused extensive flooding and damage estimated as £7 M (Kaya et al 2005). The Scottish Environmental Protection Agency (SEPA) commissioned an Early Warning system for flooding events, including the development of a hydrodynamic model (Kaya et al 2005) for forecasting dangerous surge events, which are estimated to cause £0.45 M per year damage

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