Saturday, 11 June 2016

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

Foel Fawr (SM 705 225) - 30-99m Sub-Twmpau reclassified to 30-99m Twmpau

There has been a reclassification 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 listed in the 30m–99m height band of Twmpau hills and is situated on the southern part of Ynys Dewi (Ramsey), which is an island to the west of St David’s in south-west Wales.

The hill appeared in the original Welsh P30 listings on Geoff Crowder’s website and was included in the Sub-List adjoined to the 30m-99m height band of hills, and was the only hill listed in this Sub-List under the grouping of the Pembrokeshire Islands.

The Trimble GeoXH 6000 survey that resulted in this hill’s reclassification was conducted on the 15th May 2016 in the mid-afternoon 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 from where the boat docks as a gravelled track leads up to The Farmhouse from where a good path heads toward the southern part of the island.

The name of the hill is Foel Fawr and it is given a 72m summit spot height on current Ordnance Survey maps, and has been listed with an estimated bwlch height of c 43m based on bwlch contouring between 40m – 45m, these values gave the hill c 29m of drop and therefore it remained listed as a Sub-Twmpau.

Two points were surveyed for summit position and also for bwlch position, these are given below:

Summit 1:  72.0m (71.954m, converted to OSGM15)) at SM 70542 22567

Summit 2:  71.8m (71.821m, converted to OSGM15) at SM 70539 22566

Bwlch 1:  41.8m (41.764m, converted to OSGM15)) at SM 70504 22667

Bwlch 2:  41.9m (41.899m, converted to OSGM15) at SM 70511 22665

The surveys for bwlch position were conducted on the valley to valley traverse and therefore the higher result is taken when calculating the drop value for the hill. 

Therefore the survey with the Trimble GeoXH 6000 resulted in a 72.0m (converted to OSGM15) summit height and a 41.9m (converted to OSGM15) bwlch height, with these values giving the hill 30.1m of drop.  As the minimum drop for qualification to the main Twmpau list is 30m this means that Foel Fawr is reclassified from a Sub-Twmpau to a Twmpau.

The full details for the hill are:

Cardinal Island:  Ynys Dewi

Summit Height:  72.0m (converted to OSGM15)

Name:  Foel Fawr

OS 1:50,000 map:  157

Summit Grid Reference:  SM 70542 22567

Drop:  30.1m (converted to OSGM15)

Foel Fawr (SM 705 225) now reclassified from a Sub-Twmpau to a Twmpau

Myrddyn Phillips (May 2016)

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