Flooding from the sea can be caused by overflow, overtopping and breaching of flood defences like dykes and breaching of natural barriers, like coastal dunes. Land behind the coastal defences may be flooded and experience damage.
A flood from sea may be caused by a heavy storm (storm surge or tidal flood), a spring tide, or a combination of both. In addition, flooding from the sea may be exacerbated if it coincides with high river discharges. This is especially evident during the winter storm seas when low pressure weather systems are the norm. The reduced air pressure during these storms allows higher water levels – there is less pressure pushing the water down. Where flood waters from inland sources meets elevated water levels at the sea, the water cannot drain from land leading to extensive flooding in coastal locations. However, a slow rise in sea level, such as that accompanying global climate change, not necessarily leads to increased flooding of estuarine areas since the vertical sedimentation in those areas at high tide is sometimes active enough to offset the rising level of the sea.
A timely reminder of this ever present risk was the storm surge on 9th November 2007 which resulted in the highest water levels for 50 years along parts European coastlines especially in areas such as the North and Irish Seas. In the Netherlands this event led to the operation of a full scale dyke watch for the first time in 30 years. The surge also caused considerable erosion at some Wadden Islands and minor flooding in certain harbour areas. Storm surge barriers like the Thames barrier and Maeslant barrier were closed and hundreds of people were evacuated. The Xynthia storm in February 2010 caused large scale flooding damage due to storm surge in France and Portugal resulting in millions of euros of damage and a number of deaths.
Under European Legislation and responsible planning practices coastal planners and decision makers are obligated to consider coastal flooding when considering applications for coastal development and activities.
Studies and publications
- Coastal flood risk: European scale. Vulnerabilities – Global assessment(Source: ClimateChangePost.com)
- Rising Sea Level: lhavo and Vagos municipalities (South to Aveiro City) (FFCUL, Portugal)
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