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

Cnwc y Fedwen (SN 382 205) – 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 Cnwc y Fedwen (SN 382 205)

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 Cnwc y Fedwen and this was derived from the Tithe map, and it is adjoined to the Mynydd Pencarreg group of hills, which are situated in the south-western part of South Wales (Region B, Sub-Region B1), and it is positioned with a minor road to its north and south-west, and the A40 road to its south, has the town of Caerfyrddin (Carmarthen) towards the east.

When the original 100m 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 an estimated c 38m of drop and 34.23% dominance, based on the 111m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and an estimated c 73m bwlch height, based on interpolation of 5m contouring between 70m–75m that appear on the Ordnance Survey 1:25,000 Explorer 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 deletion of this hill from Lesser Dominant status is due to LIDAR analysis, resulting in a 111.3m summit height and a 74.4m bwlch height, with these values giving this hill 36.9m of drop and 33.16% of dominance, which is insufficient for this hill to be classified as a Lesser Dominant.

 

The full details for the hill are:

Group:  Mynydd Pencarreg

Name:  Cnwc y Fedwen

OS 1:50,000 map:  145, 159

Summit Height:  111.3m (LIDAR)

Summit Grid Reference:  SN 38266 20540 (LIDAR)

Bwlch Height:  74.4m (LIDAR)

Bwlch Grid Reference:  SN 38881 21445 (LIDAR)

Drop:  36.9m (LIDAR)

Dominance:  33.16%

 

Myrddyn Phillips (August 2022)