Monday, 7 March 2016

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


Moel y Gadair (SH 521 391) 30-99m Twmpau reclassified to 30-99m Sub-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 30–99m height band of Twmpau hills and is situated to the south-west of the small community of Pentrefelin, which is situated between Porthmadog to the east and Cricieth to the south-west.

The hill has been reclassified from a P30 Twmpau to a Sub-Twmpau, and re-joins these ranks after being originally listed in the ‘Hills to Survey’ Sub-List that appeared on Geoff Crowder’s v-g.me website.  On subsequent reassessment the hill was promoted to full P30 status due to bwlch contour interpolation, with a drop value of c 30m based on a summit spot height of 67m and an estimated bwlch height of c 37m.

The hill is named Moel y Gadair and its summit was surveyed with the Trimble GeoXH 6000 on the 15th June 2015 giving a height of 66.7m (converted to OSGM15).  On that day I misinterpreted the bwlch contouring and therefore took a number of data sets from the incorrect place.  Having re-examined Ordnance Survey mapping and driven a Google Car on the A 497 which passes over this bwlch I was confident that I now knew where the critical bwlch was positioned.

The subsequent survey of this hill’s bwlch resulted in a height value of 38.1m (converted to OSGM15), giving the hill insufficient drop to retain its P30 Twmpau status.


The full details for the hill are:

Cardinal Hill:  Moel Hebog

Summit Height:  66.7m (converted to OSGM15)

Name:  Moel y Gadair

OS 1:50,000 map:  124

Summit Grid Reference:  SH 521 391

Drop:  28.5m (converted to OSGM15)


Moel y Gadair (SH 521 391) now reclassified from a P30 Twmpau to a Sub-Twmpau with 28.5m of drop

For details on the survey that reclassified this hill from P30 Twmpau to Sub-Twmpau status please click {here} for summit and {here} for the bwlch survey.


Myrddyn Phillips (February 2016)




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