Call yourself a Geographer ?

If so, can you tell  me what’s wrong with this answer taken from a question asked in the House of Lords via the excellent theyworkforyou website…

UK: Coastline

House of Lords

Written answers and statements, 23 June 2010

Lord Laird (Crossbench)

To ask Her Majesty’s Government what is the length of the United Kingdom coastline in miles at (a) low, and (b) high, tide; and what are the lengths of the coastlines of (a) England, (b) Northern Ireland, (c) Scotland, and (d) Wales.

Baroness Hanham (Parliamentary Under Secretary of State, Communities and Local Government; Conservative)

Information provided by Ordnance Survey for Great Britain and by Land and Property Services, an agency of the Department of Finance and Personnel for Northern Ireland, indicates that the lengths of the coastlines at mean high water (MHW) and mean low water (MLW), (mean high water springs [ordinary spring tides] and mean low water springs in Scotland) are:

Country Length of Coastline at Mean Low Water (MLW) [Miles] Length of Coastline at Mean High Water (MHW) [Miles]
England 8,417 9,462
Northern Ireland 620 542
Scotland 14,675 13,186
Wales 2,323 1,999
United Kingdom 26,035 25,189

These coastal lengths include all offshore islands, and land areas which are above MLW.

The precise length of coastlines will vary from time to time due to natural and gradual changes arising from coastal erosion and silt deposition.

Written and submitted from Warsaw Airport (52.177N, 20.974E)

24 replies on “Call yourself a Geographer ?”

The area of land is greater during a low tide – so it doesn’t make sense that the length of coastline for England would be LESS than during a high tide (when the area is less than during a high tide).

A quality answer always depends on the quality of the question. In my (now past) professional job, I was asked to give the lengths of the coastline for each English county, based on OS’s MHW. A few raised eyebrows when Nottinghamshire turned in a longer coastline than West Sussex…

Ah, but of course it can. At high tide many sections of land will become islands therefore giving the possibility of increasing the overall length of coastline. I’m not saying this is correct, but surely it is possible…?

David is right. There’s another situation which may contribute to odd answers – where MLW is coincident with MHW, the OS omit MLW info, even at large scales. It all shows the dangers of merely adding up numbers in a GI dataset.

Re the length of the coast at high tide, it’s possible that its longer because you could generate many inlets that didn’t exist at low tide, and, as David notes, you could also genearate more islands

Hypothetically, a given length of MHW coastline, being shaped by the combined effects of wind, sea and river, could be typically longer than the same length of MLW coastline, the latter being shaped only by the sea and hence smoother. The effect is probably greater if we consider fractal coastlines.

It makes perfect sense. At low tide the coastline is nice and straight along the sand, smooths out all the crinkles. When tide is high, the water comes up to all those crinkles in the coastline and hence the coastline is longer. Of course, the area of the country increases massively at low water I imagine. This makes perfect sense to me, I don’t see what the problem is???

Ah, well spotted David! I was trying to create some scenario like that to explain the figures but didn’t think of idland-tops. Nice!

I think it is plausible. But depends on the nature of the country looking at. I’ve been to England only twice but I have a coast with a rocky cliff in mind that stands on a sandy beach (or gravel) that is exposed at low tide and flooded at high tide. At low tide you have a straight line of coast on the sand at high tide when the water level reaches to the rocks every edge and curve in it adds up to the coastline.
A larger circumference is not necessarly linked to a large area. That is very basic geometry.

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