[Tagging] Coastal beach definition for mapping.

[Warin]

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
>
> 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
>
> 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

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

Arrr the visitors centre says tidal flats ..
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/

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.