Mapping Mountains – Hill Reclassifications – Y Trichant - The 300m Hills of Wales

Cefn Gwrhyd (SN 73107 08600 and SN 73109 08601) – Sub-Trichant reclassified to Trichant

There has been a reclassification to the list of Y Trichant – The 300m Hills of Wales, 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 Cefn Gwrhyd (SN 731 086)

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

Y Trichant – The 300m Hills of Wales – Welsh hills at or above 300m and below 400m in height that have 30m minimum drop, with an accompanying sub list entitled the Sub-Trichant, with the criteria for this sub category being all Welsh hills at or above 300m and below 400m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips with the Introduction to the list and the renaming of it appearing on Mapping Mountains on the 13^th May 2017, and the Introduction to the Mapping Mountains publication of the list subsequently appearing on the 1^st January 2022. 

Y Trichant - The 300m Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Cefn Gwrhyd, and it is adjoined to the Mynydd Du group of hills, which are situated in the southern part of South Wales (Region B, Sub-Region B5), and it is positioned with the A474 road to its west, the A4068 road to its north and the A4067 road to its south-east, and has the town of Pontardawe towards the south, and the villages of Brynaman towards the north and Ystalyfera towards the east.  

When the original 300m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill appeared in the accompanying Hills to be surveyed sub list as it did not meet the criteria then used for the main P30 list.

When 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 an estimated c 29m of drop, based on an estimated c 303m summit height and an estimated c 274m bwlch height, with each based on interpolation of 10m contouring.

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

Since the original publication of the Welsh P30 lists on Geoff Crowder’s v-g.me website there have been a number of maps made available online.  Some of these are historic such as the series of Six-Inch maps on the National Library of Scotland website.  Whilst others were digitally updated such as the Ordnance Survey Vector Map Local that was hosted on the Geograph website and which was entitled the Interactive Coverage Map, whilst others are current and digitally updated such as the interactive mapping on the Magic Maps and WalkLakes websites.

The details for this hill were re-assessed when the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map became available online.  This mapping had many spot heights not on other publicly available Ordnance Survey maps and for this hill it had a 304m summit spot height and a 275m bwlch spot height, with these values giving this hill 29m of drop.

Extract from the Ordnance Survey Interactive Coverage Map hosted on the Geograph website showing the summit spot height

Extract from the Ordnance Survey Interactive Coverage Map hosted on the Geograph website showing the spot height on the area of this hill's bwlch

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 reclassification of this hill from Sub-Trichant status is due to LIDAR analysis, resulting in a 305.5m summit height and a 274.8m bwlch height, with these values giving this hill 30.7m of drop, which is sufficient for it to be classified as a Trichant. 

The full details for the hill are:

Group:  Mynydd Du

Name:  Cefn Gwrhyd

OS 1:50,000 map:  160

Summit Height:  305.5m (LIDAR)

Summit Grid Reference:  SN 73107 08600 and SN 73109 08601 (LIDAR)

Bwlch Height:  274.8m (LIDAR)

Bwlch Grid Reference:  SN 73885 09967 (LIDAR)

Drop:  30.7m (LIDAR)

Myrddyn Phillips (March 2019)