Mapping Mountains – Hill Reclassifications – 30-99m Twmpau

 

Moel Coed Helen (SH 475 623) – 30-99m Sub-Twmpau reclassified to 30-99m Twmpau 

There has been confirmation of a reclassification to the list of 30-99m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Moel Coed Helen (SH 475 623)

The criteria for the list that this reclassification applies to are:

30-99m Twmpau – Welsh hills at or above 30m and below 100m in height that have 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 30m and below 100m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

30-99m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Moel Coed Helen, and it is adjoined to the Yr Wyddfa group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with a minor road to its north, west and east, and the A487 road to its east, and has the town of Caernarfon towards the north-east.

When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for the main P30 category.

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 31m of drop, based on the 48m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated c 17m bwlch height, based on interpolation of 5m contouring between 15m – 20m. 

Extract from the Ordnance Survey 1:25,000 Explorer map

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales.

Therefore, the confirmation of the reclassification of this hill from 30-99m Sub-Twmpau status is due to LIDAR analysis, resulting in a 48.5m summit height and a 17.1m bwlch height, with these values giving this hill 31.3m of drop, which is sufficient for it to be classified as a 30-99m Twmpau. 

 

The full details for the hill are: 

Group:  Yr Wyddfa 

Name:  Moel Coed Helen 

OS 1:50,000 map:  114, 115

Summit Height:  48.5m (LIDAR) 

Summit Grid Reference:  SH 47595 62389 (LIDAR)               

Bwlch Height:  17.1m (LIDAR) 

Bwlch Grid Reference:  SH 47721 62272 (LIDAR) 

Drop:  31.3m (LIDAR) 

 

Myrddyn Phillips (June 2025)