Submergent Coastlines

If you hunted for some more rias after last week’s post, you will have discovered that they are mainly on the south coast of England.  This coast is a submergent coastline.  It is becoming submerged as the sea level rises relative to the land.

So why don’t all of Britain’s coasts have rias?  Surely the sea is rising everywhere right?

Yes, it is, by about 20 cm from 1880 to 2009.

But in other parts of Britain the land is rising too.  In the south the land is sinking by about 3 cm per 100 years.

So the sea level is going up and at the same time the land is sinking down.  The possibility of flooding increases year by year.

Along the ria of the River Colne the path was up on a raised bank above the marshland.

There were places where the rising tide could flow through the bank to maintain the wetland on the other side, but the amount getting through could be controlled.

Further up the Colne, at Wivenhoe, a flood barrier has been installed in the river, and embankments stretch onto the land either side.  Lock gates can be closed to prevent excessively high tides flooding Colchester.


Photo by Ben Pearson

Flood barriers are being closed more and more frequently as the land in this area continues to sink and the sea continues to rise.  The coastline is becoming more and more artificial, as barriers are built, strengthened and raised to continue to keep out the sea.

At what point should we give up the fight?

It depends on what is being protected.  The more valuable the land and buildings, the more money is likely to be available for building suitable flood defences.  There’s already talk of Thames Barrier 2, further downstream, to secure the future of London.