Mapping Mountains – Hill Reclassifications – Y Trechol – The Dominant Hills of Wales

 

Mynydd Cas-fuwch (SN 028 296) – Lesser Dominant deletion

There has been a deletion to the list of the Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop, dominance and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Mnydd Cas-fuwch (SN 028 296)

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

Y Trechol - The Dominant Hills of Wales - Welsh P30 hills whose prominence  equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height.  The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015, and the list is now available inits entirety on Mapping Mountains in Google Doc format. 

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The name the hill is now listed by is Mynydd Cas-fuwch, and it is adjoined to the Mynydd Preseli group of hills, which are situated in the south-western part of South Wales (Region B, Sub-Region B1), and it is positioned with minor roads to its north-west and south, the B4329 road to its south-east and the B4313 road to its north-east, and has the village of Cas-mael (Puncheston) towards the west. 

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

When the original 300m height band of Welsh P30 hills published on Geoff Crowder’s v-g.me website were standardised and interpolated heights and drop values also included, this hill was listed with 116m of drop and 33.43% dominance, based on the 347m summit spot height adjoined to a triangulation pillar that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and the 231m bwlch spot height that appears on the Ordnance Survey 1:50,000 Landranger map. 

Extract from the Ordnance Survey 1:50,000 Landranger 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 Lesser Dominant status is due to LIDAR analysis, resulting in a 346.4m summit height and a 231.5m bwlch height, with these values giving this hill 114.9m of drop and 33.17% dominance, which is insufficient for this hill to be classified as a Lesser Dominant.

 

The full details for the hill are:

Group:  Mynydd Preseli

Name:  Mynydd Cas-fuwch

OS 1:50,000 map:  145, 157, 158

Summit Height:  346.4m (LIDAR)

Summit Grid Reference:  SN 02872 29646 (LIDAR)

Bwlch Height:  231.5m (LIDAR)

Bwlch Grid Reference:  SN 05870 29855 & SN 05868 29843 (LIDAR)

Drop:  114.9m (LIDAR)

Dominance:  33.17% (LIDAR)

 

Myrddyn Phillips (March 2023)