Explaining erosion in simple terms

A letter recently appeared in the weekly Great Yarmouth Mercury from reader B. J. Rudd, who demonstrated an acute and perceptive understanding of the mechanism as to why the sand is being lost from our beaches.

His ‘theory’ is in fact just what’s happening, but not dressed up in the complex terminology of coastal geomorphology that is employed in describing the mechanism of sand flow made in some scientific studies. It matches the recent Crown Estate findings, yet employs simple observation and a good knowledge of the behaviour of the sea and shoreline of the area.

His letter in full is repeated below:

“For the last 30 days I have been keeping a log of the “sand-suckers” working off the coast, anything from four to six miles off. Whenever I’ve seen one, I’ve gone to “ais live free” on the computer and noted down her details”

I might have missed one or two but the ones I saw amounted to 27″

“Their dead weights (dw) as given on the website, ranged from approximately 5,000 to 12,000 tons. Here, I must admit I was never very bright at understanding tonnages, however, the dredgers with a dw of 12,000 tons would possibly have about 10,000 tons of sand on board when fully laden. The smaller ones of 5,000 tons dw would probably have 3,500 tons”

“Perhaps some of your readers would be kind enough to comment on that. Using those parameters it seems as if approximately 143,000 tons of sand have been taken in 30 days. Let’s say one month”.

“So, in the course of a year, it comes to an horrendous amount.It’s wrong to multiply the figures more than that as, in the years gone by, the extraction rate might have been smaller. But it has been going on for a long time. Probably about 30 years”

“Sand and small stones are held in suspension in the water. If you’ve ever stood in the sea, especially on spring tides, you might have felt the prickly sensation on your legs”

“That’s what I’m talking about. That’s the sand in suspension being carried along by the tide”.

“As lots of your readers know, the flood tide runs from north to south and reverses on the ebb”

“So, in an ideal world, the sand is carried north on the ebb. It settles out a bit at slack water and is then brought back to the same place on the flood”

“Now we come to a little bit of theory. What about if, on the flood, some of the sand is carried out to sea and settles in the holes being dug by the dredgers. At first glance at a chart, it 
seems as if the channel which connects Yarmouth harbour to the to the open sea runs roughly parallel to the coastline south of the harbour”.

“Imagine, then, the flood tide coming down the Yarmouth Roads, loaded with sand it had picked up from beaches along the way”.

“It’s flow is restricted, in a way, by the Scroby bank. It’s a very strong force. It has to go somewhere. It needs to break out”

“Some of it going south into Gorleston roads and some of it going down the Holm channel out to sea to the area where the dredging takes place. 
I know it’s theory but there might just be something in it”

B J RUDD
Warren Road,
Gorleston


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