On 04/04/18 07:56, Warin wrote:
On 03/04/18 18:32, Christoph Hormann wrote:
On Monday 02 April 2018, Warin wrote:
The present OSM wiki defintion for beach
is "Coastal beaches should be mapped down to the mean high water
spring line (natural
<https://wiki.openstreetmap.org/wiki/Key:natural>=coastline
<https://wiki.openstreetmap.org/wiki/Tag:natural%3Dcoastline>)"
(from https://wiki.openstreetmap.org/wiki/Tag:natural=beach)
I think this is incorrect .. they should be mapped past the high
water mark to the low water mark.
This has been a disputed subject for a long time. In any case the wiki
clearly does not reflect the current use of the tag here though. The
following situations exist frequently in reality:
a) coast at high water line, beach only above high water line. This
leads to very narrow beaches since the area correctly to be tagged as a
beach is only between the regular high water line and the extreme
(storm flood) high water line.
b) coast at high water line, beach down to lower end of beach (either
the low water line or the transit of the beach to a tidal flat -
sometimes, in particular in the UK, the tidal flat is also incorrectly
tagged natural=beach).
c) coast at an intermediate water level (the level shown in whatever
image is used), beach ends at this water level (i.e. mappers directly
draw what they see in the image).
All variants are common, (a) in my experience is not more common than
(b).
For clarity regarding the difference between beaches and tidal flats: A
beach is formed by waves, it therefore always has a significant slope
and is rarely wider than a few hundred meters. A tidal flat is a flat
area exposed at low tide that is shaped by the tidal currents.
Thanks Christoph, had not considered 'tidal flats'...
there are some large areas I know of ...
was thinking about them while I considered 'beaches', but had not
considered the term 'tidal flats'.
Humm tidal flats are sometimes called 'mud flats' ...
Came across this from the US Army https://definedterm.com/a/document/10633
tidal flats - (1) _Marsh <https://definedterm.com/a/definition/88100>_y
or muddy areas covered and uncovered by the rise and fall of the _tide
<https://definedterm.com/a/definition/88503>_. A TIDAL MARSH. (2) _Marsh
<https://definedterm.com/a/definition/88100>_y or muddy areas of the
seabed which are covered and uncovered by the rise and fall of tidal water.
beach - The zone of _unconsolidated
<https://definedterm.com/a/definition/88535>_ material that extends
landward from the _low water line
<https://definedterm.com/a/definition/88065>_ to the place where there
is marked change in material or physiographic form, or to the line of
permanent vegetation (usually the effective limit of storm _wave
<https://definedterm.com/a/definition/88560>_s). The seaward limit of a
beach--unless otherwise specified--is the mean _low water line
<https://definedterm.com/a/definition/88065>_. A beach includes
_foreshore <https://definedterm.com/a/definition/87684>_ and _backshore
<https://definedterm.com/a/definition/86032>_. (See Figure A-1) See also
SHORE, SUSTAINABLE BEACH, and SELF-SUSTAINING BEACH, and TIDELANDS.
So a 'beach' may include a 'tidal flat' ... confused.
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