Mapping Mountains – Hill Reclassifications – 100m Twmpau

Bryn Hywel (SH 515 417) – 100m Sub-Twmpau deletion

There has been a deletion from the list of 100m 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 Bryn Hywel (SH 515 417)

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

100m Twmpau – Welsh hills at or above 100m and below 200m in height that have 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

100m Twmpau by Myrddyn Phillips

The name the hill is listed by is Bryn Hywel, and it is adjoined to the Moel Hebog group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with minor roads to its west and south, the A487 road to its north-east, the B4411 road farther to its west and the A497 road farther to its south, and has the town of Cricieth towards the south south-west.

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was mistakenly included in the main P30 list.

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-assessed and it was reclassified to 100m Sub-Twmpau status and listed with an estimated c 21m of drop, based on the 159m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and an estimated c 138m bwlch height, based on interpolation of 10m contouring between 130m – 140m. 

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 deletion of this hill from 100m Sub-Twmpau status is due to LIDAR analysis, resulting in a 158.7m summit height and a 139.6m bwlch height, with these values giving this hill 19.1m of drop, which is insufficient for it to be classified as a 100m Sub-Twmpau. 

 

The full details for the hill are: 

Group:  Moel Hebog 

Name:  Bryn Hywel 

OS 1:50,000 map:  124

Summit Height:  158.7m (LIDAR) 

Summit Grid Reference:  SH 51520 41737 (LIDAR) 

Bwlch Height:  139.6m (LIDAR) 

Bwlch Grid Reference:  SH 51674 41306 & SH 51675 41305 (LIDAR) 

Drop:  19.1m (LIDAR) 

 

Myrddyn Phillips (May 2024)