Feeling the squeeze
Last week we witnessed an incredible meteorological exhibition. At the time of writing this, the extent of the storm’s damage is not fully known, but initial indications would suggest we got away with it by-and-large this time. I write that while touching a large chunk of driftwood.
A combination of storm force winds and incredibly low pressures, coinciding with a cycle of very high spring tides, was a recipe for widespread flooding in low-lying areas throughout the South West peninsular. If we can be glad of anything it is that an important member of the flooding trinity, swollen rivers, was not present or the impacts could have been far more severe.
So what lies behind last week’s drama? Well, just like a shampoo commercial “you’re worth it” sorry, not that one, “pay attention; here comes the science”.
Firstly, what causes the tide?
If you think of the planet’s surface water as a skin covering the globe, then that ‘skin’ is pulled by the gravitational forces of the moon, creating a bulge in its surface. This pulls the ‘skin’ into an ellipse with two bulges and two thin sections – the bulges are high tides and the thin sections the low. As the moon orbits the earth so the bulges circum-navigate the world, creating the twice daily rise and fall of the tides, a cycle of four states completed in a little less than 25 hours.
Don’t be fooled by the name, a spring tide happens every other week due to the lunar cycle combining with the extra (but much smaller) gravitational pull of the sun, with every other spring tide being a super-high spring. It’s got nothing to do with the time of year, but rather that the sea level ‘springs’ up. That said, to confuse everyone further the biggest springs normally occur in the Spring and Autumn! Last Monday’s forecast high water level at Exmouth was 4.1 metres above chart datum, which is as big as the predictions get for this area.
Tides can also be exaggerated by low pressure, as the surface of the sea is ‘sucked’ even higher relative to the land. High pressure conversely pushes down sea level. On Monday the pressure dropped below 960 millibars, one of the lowest readings ever recorded.
Finally, the winds created by this mega low pressure were a major factor. Not only did the ferocity of the storm force winds whip the sea up into even bigger waves, but the action of wind physically pushed a greater volume of water toward the shore, and into the estuary mouth. We were fortunate that the wind direction was from the west, Exmouth benefited from a sheltered location at the apex of Lyme Bay. Had these winds been due south, the Bay might have acted like a giant funnel collecting water on our doorstep.
So, Exmouth weathered the storm, as it has weathered many through the centuries of its maritime history. Perhaps we should spare a thought for those less fortunate… or perhaps not, you be the judge.
A little further east, on the south Hampshire coast, a large static caravan park had been given permission to construct large sea defences to protect its low lying location. Now to build these defences, heavy machinery was driven over a SSSI coastal habitat, leading to its deterioration, and the defences themselves were dumped on top of SSSI geological features of the coast. A couple of environmental infringements I find exasperating, not to mention woefully short-sighted.
However when last week’s storm hit the site the defences didn’t work. Instead they created something resembling a lagoon behind the beach, in which the static caravans were photographed bobbing about like monstrous white hippopotamuses.
The fact is that coastal squeeze is a very real issue in our little island Nation. Pressures, both natural and man-made, are greater than ever before on our coastal fringes. More and more people want a house with a sea view, while increased storm activity and predicted sea level rise mean that some areas of the coast are being nibbled away, while other areas are being gobbled up.
Historically our reaction to the natural process of coastal erosion was to confront nature, and bung in a load of ugly and impotent features like groynes and gabions. Where defences were put in place to preserve beach materials, in spite of the clawing forces of long shore drift, the immediate area might indeed benefit; but normally this was at the detriment of another site further down the coast.
The policy now being promoted is one of ‘managed retreat’ which broadly translates as admitting when you’re beat and allowing the process to take its course. So is this a terrifying modern strategy? Not really, especially when you consider it was over a thousand years ago that King Canute realised no-one can control the oceans, no matter how powerful a person you may be.