The message from "ARWadsworth" contains these words:
I am sure they have. There was once a thick layer of peat there and that started shrinking as it dried out after it was drained and intensive cultivation has also contributed to loss of bulk.
Peat 'mining' has affected it too, I imagine.
Mary
OS Mean Sea Level is also defined by reference to Newlyn "the Ordnance Datum, which is the mean level of the sea at Newlyn in Cornwall, which was calculated from hourly readings of the sea level recorded on a automatic tide gauage from 1 May 1915 to 30 April 1921."[1]
The Survey height will be relative to the Geodetic Datum so at any point 'height above sea level' is a conventional value that may be well above or below the real level of the sea thereabouts.
[1] Harley. Ordnance Survey Maps, a descriptive manual. 1975
Er actually it's more than a foot a century. If you don't believe me, go and look how many times they've had to raise Victoria embankment by the Thames.
IIRC the Thames Flood Barrier was expected to be effective for 30-50 years from commissioning.
Bad form to folow up oneself, but :
Reminds me of 'The Kraken Wakes..' ;-)
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