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

Moel y Gadair (SH 521 391) 30-99m Twmpau reclassified to 30-99m Sub-Twmpau

This hill has subsequently been reinstated to 30-99m Twmpau status due to LIDAR analysis indicating this hill is a natural P30, with the raised road passing over the bwlch considered a relatively recent man-made construct; therefore it is excluded from the height of the bwlch.

There has been a reclassification to the listing of 30-99m Twmpau (thirty welsh metre prominences and upward) due to a survey with the Trimble GeoXH 6000 and subsequent LIDAR analysis.  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 30-99m Twmpau to a 30-99m Sub-Twmpau, and re-joins these ranks after being originally listed in the Hills to be surveyed Sub-List that appeared on Geoff Crowder’s v-g.me website.  On 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 15^th June 2015 giving a height of 66.7m.  During the 15^th June 2015 survey the contours at the bwlch were misinterpreted resulting in the second bwlch survey which was conducted on the 23^rd February 2016 and the subsequent LIDAR analysis resulting in a bwlch height of 36.8m.

Therefore, the reclassification of this hill to 30-99m Sub-Twmpau status is due to a 66.7m summit height and a 36.8m bwlch height, with these values giving this hill 29.9m of drop which is insufficient for 30-99m Twmpau status.

The full details for the hill are:

Group:  Moel Hebog

Summit Height:  66.7m (converted to OSGM15)

Name:  Moel y Gadair

OS 1:50,000 map:  124

Summit Grid Reference:  SH 52165 39135

Drop:  29.9m (Trimble summit and LIDAR bwlch)

Moel y Gadair (SH 521 391) now reclassified from a 30-99m Twmpau to a 30-99m Sub-Twmpau

For details on the summit survey and the bwlch survey that resulted in this hill being reclassified to a 30-99m Sub-Twmpau status.

My thanks to Aled Williams for his initial LIDAR analysis

Myrddyn Phillips (February 2016)