[Tagging] Coastal beach definition for mapping.

Warin 61sundowner at gmail.com
Thu Apr 5 21:36:09 UTC 2018

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 <61sundowner at gmail.com 
> <mailto:61sundowner at 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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