Mapping Mountains – Hill Reclassifications – 200m Twmpau

 

Pen y Bryn (SO 075 896) – 200m Sub-Twmpau addition

There has been confirmation of an addition of a hill to the list of 200m 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 Pen y Bryn (SO 075 896)

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

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 200m and below 300m 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. 

200m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Pen y Bryn and this was derived from the Tithe map, and it is adjoined to the Hirddywel group of hills, which are situated in the northern part of South Wales (Region B, Sub-Region B2), and it is positioned with minor roads to its west, south and east, and the A489 road to its north-east, and has the town of Y Drenewydd (Newtown) towards the east north-east.

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was not included in the accompanying Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub 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 27m of drop, based on the 239m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and the 212m bwlch spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map. 

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 addition of this hill to 200m Sub-Twmpau status is due to LIDAR analysis, resulting in a 238.6m summit height and a 210.5m bwlch height, with these values giving this hill 28.1m of drop, which is sufficient for it to be classified as a 200m Sub-Twmpau. 

 

The full details for the hill are: 

Group:  Hirddywel 

Name:  Pen y Bryn 

OS 1:50,000 map:  136

Summit Height:  238.6m (LIDAR) 

Summit Grid Reference:  SO 07529 89658 (LIDAR) 

Bwlch Height:  210.5m (LIDAR) 

Bwlch Grid Reference:  SO 07074 89710 (LIDAR) 

Drop:  28.1m (LIDAR) 

 

Myrddyn Phillips (March 2025)