Professor Nicholas Day speaks with BBC Guernsey about planning for a rise in sea level and storm surges

September 28th, 2011 by Professor Nicholas Day

Professor Nicholas Day, CBE, FRS speaks with BBC Guernsey about planning for a rise in sea level and storm surges (click image to expand - ©RLLord)

When Guernsey last produced a report on its coastal defenses the scientific community stated that we should take into account a sea level rise of 70 to 80 centimetres by the end of the century.

A lot of scientific work in the last five years now suggests that the sea level could potentially rise by 1 to 1.5 metres (five feet) by the end of the 21st century.  When witnessing a high spring tide you can imagine what an extra five feet of sea level would do to our coastline.  The whole area would be swamped.

St Peter Port waterfront floods on a high spring tide (click image to expand - ©RLLord)

There is obviously a large amount of uncertainty in these estimates but many authorities are taking this information very seriously.  The Dutch are very worried about the rise in sea level. They have set-up their Delta Commission. They are taking into account a predicted sea level rise of 1.3 metres or four feet by the end of the century.

The committee responsible for London’s plan to deal with sea level rise is adopting what is called in the UK the H++ scenario which looks at sea level rise of 1 metre, possibly two metres. They regard the 2 metre scenario as extremely unlikely but up to 1.5 metres (five feet) is quite a plausible upper limit.

We expect a slow increase in sea level over the next 90 years and then over the next 100 years after that.

Guernsey should be planning long-term on how the island might defend itself against the predicted rise in sea level.

The States of Guernsey were meant to release a report now on the effects of sea level rises on coastal defences.  That report has now been delayed. That is not surprising because the States of Guernsey has very difficult decisions to make.

If they adopt the same maximum sea level rise as published in the 2007 Royal Haskoning report it is not going to have much credibility but if they adopt the sort of approach taken by the Dutch and the authorities responsible for the Thames and London then they have some very serious thinking to do.

It’s not just sea level rise long term over decades and decades that has to be thought about.  One has to think of sea surges as well.

In March 2008 the sea wall at Rocquaine was fractured by a particularly violent sea surge.

The Rocquaine Bay seawall toppled by the storm surge of 10 March 2008 (click image to expand - ©RLLord)

More recently than that, at the end of February 2010 – cyclone Xynthia, a storm that received very little publicity in the UK – came up the Bay of Biscay. It was heading towards Guernsey but it turned eastwards and hit the French coast of the Vendée and the Charente Maritime.

Over fifty people were killed, most of the coastal defences over a large area were destroyed, and that has led the French to rethink how they are going to deal with their sea defences. Every coastal commune in France is required to produce a coastal defence plan, which is based on the recommendations of the central French government that sea level rise may be up to 1.5 metres over the next century, but more important than that, sea surges may rise by 1.5 metres (five feet) at any time as happened along the French Atlantic coast last year. These are the sort of risks that Guernsey should be considering how it can best defend itself against.

Guernsey could also be doing more on the global stage. Prevention is better than cure. One is talking about a five foot rise in sea level if nothing is done to prevent global warming. Unfortunately the greenhouse gases that are causing this warming are increasing in the atmosphere. The concentrations of these gases are actually accelerating at the moment.

Unless the global community gets together to reduce emissions and curb what is currently going on then the worst scenarios may well occur. Guernsey could be doing much more on the international stage. Small islands around the world are punching well above their weight – the Pacific islands and the Caribbean islands are getting together to make a powerful impact on the international stage. Guernsey should be working very closely with them.


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