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<div class="moz-cite-prefix">On 04/04/18 07:56, Warin wrote:<br>
</div>
<blockquote type="cite"
cite="mid:11eaf958-1d46-93be-82b2-dbc93157052c@gmail.com">On
03/04/18 18:32, Christoph Hormann wrote:
<br>
<blockquote type="cite">On Monday 02 April 2018, Warin wrote:
<br>
<blockquote type="cite">The present OSM wiki defintion for beach
<br>
<br>
is "Coastal beaches should be mapped down to the mean high
water
<br>
spring line (natural
<br>
<a class="moz-txt-link-rfc2396E" href="https://wiki.openstreetmap.org/wiki/Key:natural"><https://wiki.openstreetmap.org/wiki/Key:natural></a>=coastline
<br>
<a class="moz-txt-link-rfc2396E" href="https://wiki.openstreetmap.org/wiki/Tag:natural%3Dcoastline"><https://wiki.openstreetmap.org/wiki/Tag:natural%3Dcoastline></a>)"
<br>
<br>
(from <a class="moz-txt-link-freetext" href="https://wiki.openstreetmap.org/wiki/Tag:natural=beach">https://wiki.openstreetmap.org/wiki/Tag:natural=beach</a>)
<br>
<br>
I think this is incorrect .. they should be mapped past the
high
<br>
water mark to the low water mark.
<br>
</blockquote>
This has been a disputed subject for a long time. In any case
the wiki
<br>
clearly does not reflect the current use of the tag here
though. The
<br>
following situations exist frequently in reality:
<br>
<br>
a) coast at high water line, beach only above high water line.
This
<br>
leads to very narrow beaches since the area correctly to be
tagged as a
<br>
beach is only between the regular high water line and the
extreme
<br>
(storm flood) high water line.
<br>
<br>
b) coast at high water line, beach down to lower end of beach
(either
<br>
the low water line or the transit of the beach to a tidal flat -
<br>
sometimes, in particular in the UK, the tidal flat is also
incorrectly
<br>
tagged natural=beach).
<br>
<br>
c) coast at an intermediate water level (the level shown in
whatever
<br>
image is used), beach ends at this water level (i.e. mappers
directly
<br>
draw what they see in the image).
<br>
<br>
All variants are common, (a) in my experience is not more common
than
<br>
(b).
<br>
<br>
For clarity regarding the difference between beaches and tidal
flats: A
<br>
beach is formed by waves, it therefore always has a significant
slope
<br>
and is rarely wider than a few hundred meters. A tidal flat is
a flat
<br>
area exposed at low tide that is shaped by the tidal currents.
<br>
<br>
</blockquote>
Thanks Christoph, had not considered 'tidal flats'...
<br>
there are some large areas I know of ...
<br>
was thinking about them while I considered 'beaches', but had not
considered the term 'tidal flats'.
<br>
<br>
</blockquote>
<br>
Humm tidal flats are sometimes called 'mud flats' ... <br>
Came across this from the US Army
<a class="moz-txt-link-freetext" href="https://definedterm.com/a/document/10633">https://definedterm.com/a/document/10633</a><br>
tidal flats - (1) <u><a
href="https://definedterm.com/a/definition/88100"
class="term-pullover hidden-xs hidden-sm" data-container="body"
data-toggle="popover" data-trigger="hover" data-placement="left"
data-content="(1) A tract of soft, wet land, usually vegetated
by reeds, grasses and occasionally small shrubs. (2) Soft, wet
area periodically or continuously flooded to a shallow depth,
usually characterized by a particular subclass of grasses,
cattails and other low plants." data-original-title="" title="">Marsh</a></u>y
or muddy areas covered and uncovered by the rise and fall of the <u><a
href="https://definedterm.com/a/definition/88503"
class="term-pullover hidden-xs hidden-sm" data-container="body"
data-toggle="popover" data-trigger="hover" data-placement="left"
data-content="The periodic rising and falling of the water that
results from gravitational attraction of the Moon and Sun and
other astronomical bodies acting upon the rotating Earth.
Although the accompanying horizontal movement of the water
resulting from the same cause is also sometimes called the tide,
it..." data-original-title="" title="">tide</a></u>. A TIDAL
MARSH. (2) <u><a href="https://definedterm.com/a/definition/88100"
class="term-pullover hidden-xs hidden-sm" data-container="body"
data-toggle="popover" data-trigger="hover" data-placement="left"
data-content="(1) A tract of soft, wet land, usually vegetated
by reeds, grasses and occasionally small shrubs. (2) Soft, wet
area periodically or continuously flooded to a shallow depth,
usually characterized by a particular subclass of grasses,
cattails and other low plants." data-original-title="" title="">Marsh</a></u>y
or muddy areas of the seabed which are covered and uncovered by the
rise and fall of tidal water.<br>
<br>
beach - The zone of <u><a
href="https://definedterm.com/a/definition/88535"
class="term-pullover hidden-xs hidden-sm" data-container="body"
data-toggle="popover" data-trigger="hover" data-placement="left"
data-content="In referring to sediment grains, loose, separate,
or unattached to one another." data-original-title="" title="">unconsolidated</a></u>
material that extends landward from the <u><a
href="https://definedterm.com/a/definition/88065"
class="term-pullover hidden-xs hidden-sm" data-container="body"
data-toggle="popover" data-trigger="hover" data-placement="left"
data-content="The line where the established LOW WATER DATUM
intersects the shore. The plane of reference that constitutes
the LOW WATER DATUM differs in different regions."
data-original-title="" title="">low water line</a></u> 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 <u><a
href="https://definedterm.com/a/definition/88560"
class="term-pullover hidden-xs hidden-sm" data-container="body"
data-toggle="popover" data-trigger="hover" data-placement="left"
data-content="A ridge, deformation, or undulation of the surface
of a liquid." data-original-title="" title="">wave</a></u>s).
The seaward limit of a beach--unless otherwise specified--is the
mean <u><a href="https://definedterm.com/a/definition/88065"
class="term-pullover hidden-xs hidden-sm" data-container="body"
data-toggle="popover" data-trigger="hover" data-placement="left"
data-content="The line where the established LOW WATER DATUM
intersects the shore. The plane of reference that constitutes
the LOW WATER DATUM differs in different regions."
data-original-title="" title="">low water line</a></u>. A beach
includes <u><a href="https://definedterm.com/a/definition/87684"
class="term-pullover hidden-xs hidden-sm" data-container="body"
data-toggle="popover" data-trigger="hover" data-placement="left"
data-content="The part of the shore, lying between the crest of
the seaward berm (or upper limit of wave wash at high tide) and
the ordinary low-water mark, that is ordinarily traversed by the
uprush and backrush of the waves as the tides rise and fall."
data-original-title="" title="">foreshore</a></u> and <u><a
href="https://definedterm.com/a/definition/86032"
class="term-pullover hidden-xs hidden-sm" data-container="body"
data-toggle="popover" data-trigger="hover" data-placement="left"
data-content="That zone of the shore or beach lying between the
foreshore and the coastline comprising the BERM or BERMS and
acted upon by waves only during severe storms, especially when
combined with exceptionally high water. Also BACKBEACH."
data-original-title="" title="">backshore</a></u>. (See Figure
A-1) See also SHORE, SUSTAINABLE BEACH, and SELF-SUSTAINING BEACH,
and TIDELANDS. <br>
<br>
So a 'beach' may include a 'tidal flat' ... confused. <br>
<p><br>
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