I think it best to change the wiki beach front page.
At the moment only one method is mentioned ... and that is from the hi
tide and away from the water.
I think the other method - from the low tide and away from the water
should be stated too.
- On 04/04/18 20:58, Dave Swarthout wrote:
This is an interesting problem but it has no easy solution. Even if
the Wiki definition was clear, unless you happen to be able to measure
or otherwise determine the "mean high tide" line and other important
characteristics, what we map as beach or tidal flat is purely an
approximation, especially in areas having a large tidal range, as in
Alaska where I do the bulk of my mapping (20-30 feet). Satellite
imagery may offer a clear vision of beach and tidal flat but we cannot
determine the height of the tide when the photo was obtained.
Was it at high tide, low tide, or somewhere in between?
I agree that a beach is a place where wave action has created a
relatively steep slope. Other areas closer to the sea are flatter and
are often composed of finer particles, fine sand and clay, often
referred to as mud. Indeed, much of Alaska's coastline could be
characterized as mud_flat due to the large amount of solids Alaskan
rivers transport to the ocean. In my hometown of Homer, Alaska, spring
low tides can be so extreme that the water beyond the mud_flat is too
distant to see. What you can see is mud, lots of it.
Taginfo tells us that neither mud_flat or tidal_flat (or variations
without the underscore separator) are much in use, however, for some
of my mapping I've used the combination
natural=wetland
wetland=tidalflat (but it could just as easily be wetland=mudflat)
I've drawn those areas the best I can based on convenient satellite
imagery knowing full well it's merely a rough approximation. There may
not be a better solution.
Cheers,
Dave
On Wed, Apr 4, 2018 at 4:53 PM, Warin <61sundow...@gmail.com
<mailto:61sundow...@gmail.com>> wrote:
On 04/04/18 18:18, Christoph Hormann wrote:
On Wednesday 04 April 2018, Warin wrote:
So a 'beach' may include a 'tidal flat' ... confused.
I tried to explain the difference - a beach is primarily
shaped by waves
while a tidal flat is shaped by tidal currents.
The domination of waves can usually be seen in the form of a
smooth
surface where structures (like waves in the slope) typically form
parallel to the shore. Like here:
https://commons.wikimedia.org/wiki/File:The_beach_11111.JPG
<https://commons.wikimedia.org/wiki/File:The_beach_11111.JPG>
On tidal flats OTOH the water flow often form small or large
channels
like here:
https://commons.wikimedia.org/wiki/File:Waikaraka_Cycleway_from_Mangere_Bridge_IV.jpg
<https://commons.wikimedia.org/wiki/File:Waikaraka_Cycleway_from_Mangere_Bridge_IV.jpg>
Beaches can only form from relatively coarse material (sand or
coarser) - fine silt cannot form beaches because it does not
settle
fast enough in the fast moving water so the beach would
quickly erode
away. Tidal flats can form both from fine silt and coarse sand.
At coasts with a significant tidal range (like in the UK)
there is often
a beach in the upper part of the tidal range with a steeper
slope and
coarse sand and a tidal flat with less slope with either sand
as well
or finer material.
Example:
https://mc.bbbike.org/mc/?lon=-4.390229&lat=51.716636&zoom=14&num=3&mt0=bing-satellite&mt1=mapnik&mt2=google-satellite
<https://mc.bbbike.org/mc/?lon=-4.390229&lat=51.716636&zoom=14&num=3&mt0=bing-satellite&mt1=mapnik&mt2=google-satellite>
That is a very nice example, thanks .... I'd call them 'mud flats'
... :)
Broome, Western Australia has tides of ~10 meters and is know for
the 'Staircase to the Moon Festival'
where the moon is reflected off the beach/tidal flats ripples to
form a stair case up to the moon, very pretty ...
But I'm not certain if that is a tidal flat area or not ... the
imagery does not revel it ..
https://mc.bbbike.org/mc/?lon=-4.390229&lat=51.716636&zoom=14&num=3&mt0=bing-satellite&mt1=mapnik&mt2=google-satellite
<https://mc.bbbike.org/mc/?lon=-4.390229&lat=51.716636&zoom=14&num=3&mt0=bing-satellite&mt1=mapnik&mt2=google-satellite>
Arrr the visitors centre says tidal flats ..
http://www.visitbroome.com.au/discover/facts-figures/staircase-to-the-moon
<http://www.visitbroome.com.au/discover/facts-figures/staircase-to-the-moon>
There are better photos of the staircase ..
http://jksj.org/2015/06/10/broome/
<http://jksj.org/2015/06/10/broome/>
I'd still map the sand area as the beach as seen in the imagery,
think the 'tidal flat' would have one edge as the beach edge and
the rest be further out to sea.
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--
Dave Swarthout
Homer, Alaska
Chiang Mai, Thailand
Travel Blog at http://dswarthout.blogspot.com
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