Peter Miller wrote:
On 23 Aug 2009, at 15:50, Chris Hill wrote:
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.
So we need to commission a satellite to take photos every 30 minutes
for a 12 hour period for the whole of the UK at the appropriate time of
the lunar cycle - we haven't even discussed if we are should be using
neap times or spring tides or the mean of the two.
But really, I think we are starting to spit hairs here!
Britain has a huge tidal range. Just think of the difference of high
and low water at Morecambe bay or around the Wash.
The fact remains that aerial photography is not suitable for every job.
But you are free, of course, to use the level of accuracy that suits
you.
Cheers, Chris
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