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Radar reveals secrets of Chesil Beach. Is it doomed?

SCIENTISTS have been using ground-penetrating radar to find out more about the history of Chesil Beach.

Tests near Abbotsbury, Langton Herring and Ferrybridge have provided fresh clues about the evolution and internal make-up of one of the greatest features of the Dorset landscape.

Results also hint at what might happen to the beach in future, particularly if global warming causes sea levels to rise.

Experts think it may shrink – and the sea may break through it. 

Chesil Beach runs from West Bay to the Isle of Portland. Its sand and pebbles famously vary in size, getting bigger the closer they are to Portland. Coarse sand at Burton Cliffs, “horse beans” near Abbotsbury, and “hen’s eggs” at Chesil, was how De Luc described the beach’s composition in 1811.

It’s been extensively researched since the late 19th century.

“Probably the most extensive and extraordinary accumulation of shingle in the world” was how one writer described it in 1902; “an heroic piece of natural engineering” another, in 1919.

But – until now – scientists have been limited in their investigations by the very nature of the beach itself.

It’s probably impossible to dig a deep hole into the middle of a mass of sea-churned cobbles without the hole collapsing dangerously inwards…

But radar waves can go where people cannot.

Geophysical techniques have previously been deployed in places like Norfolk, Denmark and America.

And they have now been used in Dorset by Professor Matthew Bennett and Jeremy Pile from the School of Conservation Sciences at Bournemouth University, and Nigel Cassidy, from the School of Physical and Geographical Sciences at Keele University in Staffordshire.

Their findings are reported in “Internal structure of a barrier beach as revealed by ground penetrating radar (GPR): Chesil beach, UK” in the journal Geomorphology, Volume 104 (2009), pages 218–229, published by Elsevier B.V.

The authors suggest a three-phase history.

(Note: their technical language has largely been paraphrased).

Summary of radar observations

Summary of radar observations

Phase One: Chesil Beach began as a low, narrow barrier beach, possibly composed of both sand and gravel, that moved (transgressed) back towards the land because it could not keep up with rising sea levels.

Phase Two: The beach grew rapidly and bulked out, despite sea levels continuing to rise, because of a sudden abundant supply of gravel. “Although an off-shore sediment source cannot be discounted, the most likely source is the encroachment of the transgressing shore against the periglacial slope debris found in abundance along the coastal slopes of West Dorset.” In other words, material eroded from the cliffs of West Dorset was swept by the sea round Lyme Bay towards Portland and deposited – according to its size – on Chesil Beach.

Phase Three: The beach humped up (prograded) towards the sea. “This may have occurred during a more stable sea level regime or perhaps a falling regime, in the presence of continued sediment abundance… According to this model… there are three architectural components to the current beach ridge each formed in a different sea level, and sediment abundance regimes.”

Key point: if there had not been enough sediment drifting along the coast, Chesil Beach would most likely have closed in upon the land, and there might well have been no Fleet Lagoon.

Evolutionary model of Chesil Beach based on ground-penetrating radar results

Evolutionary model of Chesil Beach based on ground-penetrating radar results

Questions for the future

Prof. Bennett and his co-authors use their findings from their radar surveys to emphasise more strongly than perhaps any previous researchers the interplay of sediment abundance and sea level.

So: what will happen to Chesil Beach in future if sea levels do rise because of global warming?

And: will Chesil Beach be sufficiently replenished by material eroded from West Dorset cliffs or has that process been interrupted by developments like the new harbour at West Bay?

I asked Prof. Bennett for his thoughts (in journalistic terms rather than full-blown scientific ones) and he replied:

“Difficult to say, but I would say that without continued recharge of sediment it will decline in size, and breach; the long shore supply of sediment is unlikely to keep pace with the rate of sea level rise.

“This might be a rather pessimistic scenario and only time will tell.

“As always in these debates, the key question is the rate of sea level rise and the speed at which a system can adjust.

“I would say, however, that change is natural and you can’t set a landscape in stone, and if ultimately the beach does breach then it will simply be another chapter in its life history – you can’t halt change or ageing!”

2 Responses to “Radar reveals secrets of Chesil Beach. Is it doomed?”

  1. Horst Lindenau

    Well, nicely said. All these facts about the pebbles. Only one little thing wrong. There is no rising of the sea level. Global warming is a man-made con. More about the climate change lie you find here, find yourself a translation button from Google if you can’t understand a foreign language

  2. Charlie

    This explanation is as clear as mud, or, erm, pebbles. But visual evidence would suggest Chesil Beach would move inland in the future and indeed it has done in the recent past. Look at the old Beach Road, war time built and now covered in pebbles. So the Fleet could still yet disappear (if it is not filled in with mud before that happens!)

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