Monday, 13 June 2016

Mapping Mountains – Hill Reclassifications – 30m–99m Twmpau


Pt. 23.8m (SM 706 236) - Double Sub-Twmpau addition

There has been a confirmation of an addition to the listing of Twmpau (thirty welsh metre prominences and upward) hills due to a recent survey with the Trimble GeoXH 6000.  The hill is now listed in the Double Sub-Twmpau list adjoined to the 30–99m height band of Twmpau hills and is situated on the eastern part of Ynys Dewi, which is also commonly known as Ramsey, this is an island to the west of St David’s in south-west Wales.

The hill did not appear in the Sub-List which accompanied the original Welsh P30 listings on Geoff Crowder’s v-g.me website as the Sub-List only included hills whose map details showed that when surveyed they may stand a chance of qualification to the main P30 list, with the title of the Sub-List being ‘Hills to be surveyed.’  And as this hill only has an uppermost 20m ring contour it was judged that even when surveyed there was no chance of it reaching the dizzying heights of having a minimum of 30m of drop, and therefore it was not included in the Sub-List.  However, since first publication this Sub-List has been standardised and now includes all hills that have a minimum of 20m of drop and below 30m of drop.

The Trimble GeoXH 6000 survey that resulted in this hill’s confirmation as a Double Sub-Twmpau was conducted during the afternoon of 15th May 2016 in beautiful, sunny and still conditions.

As the hill is situated on an island the only way to approach is via boat and the only company with permission to land on Ynys Dewi is Thousand Island Adventures (tel: 01437-721721).  The hill can be easily accessed as it rises immediately above where the boat docks, however when I visited it I sought permission to do so as it is off the beaten track as far as visitors are concerned.

The hill does not possess either a map or local name and therefore the point (Pt. 23.8m) notation is being used.  It currently has an uppermost 20m ring contour encircling its summit on Ordnance Survey maps and is now joined to the remainder of Ynys Dewi by the walkway leading to the track above where the boat docks.  This walkway is elevated above the sea and is man-made, with the natural connection between this small hill and the bulk of the island being a small pebbled bit of land below the track, it is estimated that this natural land is c 2m high.

Therefore the survey with the Trimble GeoXH 6000 resulted in a 23.8m (converted to OSGM15) summit height and with an estimated bwlch height of c 2m, this hill has c 22m of drop and therefore qualifies as a Double Sub-Twmpau.


The full details for the hill are:

Cardinal Island:  Ynys Dewi

Summit Height:  23.8m (converted to OSGM15)

Name:  Pt. 23.8m

OS 1:50,000 map:  157

Summit Grid Reference:  SM 70677 23686

Drop:  c 22m



Pt. 23.8m (SM 706 236) now confirmed as a Double Sub-Twmpau


Myrddyn Phillips (May 2016)






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