[OSM-talk] Rocky beaches

[OJ W]

Hi. It's nice to see the Water Cover page anticipate a tagging question :)

Just looking at wikipedia, they say that beaches need to be formed by
gradual deposit of solids from dissolved in waves, which means (a) rocky
shorelines might not be a beach, and (b) definition of beach is confusing
enough that "rocky surface covered by tidal water" is a nice neat
unambiguous description of the feature.

Whether anything renders it is another matter... ;)


[1] http://en.wikipedia.org/wiki/Beach#Beach_formation



On Mon, Apr 14, 2008 at 4:51 PM, Steve Hill <steve at nexusuk.org> wrote:

> On Mon, 14 Apr 2008, Chris Hill wrote:
>
> > High and low water marks vary every day, the height of the tides vary a
> > lot..
>
> Correct - anyone who records high and low watermarks on maps/charts will
> be using the highest and lowest astronomical tides, not the high/low tide
> of an arbitrary day.
>
> > Most measurements are made using Mean Sea Level, which
> > doesn't change (rising sea levels aside).
>
> The options are generally to record lowest, highest or mean watermarks.
> ISTR that Ordnance Survey mark all three on their Explorer maps don't
> they?  And maritime charts rarely (never?) bother with mean - they are
> marked up in heights above/below lowest astronomical tide.
>
> >  When you look at the Yahoo
> > images, how do you know what state the tide is?
>
> You don't (other than being able to guestimate based on local knowledge).
> However, in some locations the coast line data is quite inaccurate and can
> be approximated by hand based on local knowledge and the Yahoo images.
> Some of the beaches around here (Gower, South Wales) are very flat and the
> very large tidal range of the Bristol Channel means the distance between
> high and low water marks can be over a kilometer.
>
> At the moment, nothing states what natural=coastline is actually supposed
> to be documenting, so when estimating the coastline by hand you have no
> idea whether to put it at the top of the beach, at the bottom of the beach
> or somewhere in the middle.
>
> I'm not expecting to be able to record the coastline with a huge amount of
> accuracy, but even an estimate is more accurate than the (big) distance
> between high/low water marks in some locations so defining what we are
> recording is important.
>
>  - Steve
>    xmpp:steve at nexusuk.org <xmpp%3Asteve at nexusuk.org>
> sip:steve at nexusuk.org <sip%3Asteve at nexusuk.org>   http://www.nexusuk.org/
>
>      Servatis a periculum, servatis a maleficum - Whisper, Evanescence
>
>
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