Peter Miller wrote:
On 22 Aug 2009, at 12:03, Chris Hill wrote:
Well I'm pleased that they agree
with me, but I'm not the oracle! This is another source quoting the
same general information. Do the Scottish and Northern Irish
counties generally extend to the low water mark too? Drawing from the
NPE maps seems to be our only reasonable source for the low water mark.
Great stuff.
Low water does however change much more rapidly that high water
so NPE is the 'least good' source of that date as it is 50 years old.
If one is fortunate enough to have detailed enough recent aerial
photography that that should be used.
The biggest problem with aerial photos is that you don't know what the
state of the tide was at the moment the photo was taken. You can
sometimes guess a high water mark on a beach by the strand line, but
low water is always covered except at low water.
Fyi, for Suffolk the low water mark has changed by 50 meters in
places in the past 5 years (huge amounts of shingle has arrived near
Felixstowe Ferry extending low water by that amount since I have lived
in the area). Even the high water mark has moved by many meters over 50
years in some places including Dunwich. One can see the different in
Potlatch comparing the OSM coastline with NPE base mapping.
The coast along the East Riding eroded by at least 50 metres, about 100
metres in a few places in the 50-60 years since NPE. i have been
trying to estimate the low water mark from a combination of NPE and
aerial photos of the cliff line, then moving the low water mark inland
by the same amount as the cliff has moved. Still an estimate, but a
bit better than NPE (not much updated yet). A visit with a GPS and a
camera helps, but low water is very hard to measure on the ground over
any distance because the tide comes in as you walk along! GPS and
camera helps with man-made changes.
We have good yahoo aerial photography for pasts of the coast in
Suffolk.
However... I support the idea we use best low-water source
availale for each area. It might be good to create areas between high
and low water tagged with 'shingle', 'beach' etc.
Sometimes the beach or foreshore reaches much higher than the high
water mark, but not usually on quickly eroding coastlines so NPE would
be good there.
Should be also use low water as the edge of 'Wales' itself or
has any evidence for the 3 mile limit mentioned by the wiki by someone
been found?
Good question, and what about the 12nm limit?
Regards,
Peter
Cheers, Chris
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