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

Pen y Bwlch Coch (SH 751 159) – 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 detail produced by JoeNuttall in his surface analysis progamme, with subsequent LIDAR analysis conducted by the DoBIH team and independently by Myrddyn Phillips. 

LIDAR image of Pen y Bwlch Coch (SH 751 159)

The criteria for the list that this reclassification 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 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 Pen y Bwlch Coch, and it is adjoined to the Cadair Idris group of hills, which are situated in the south-western part of North Wales (Region A, Sub-Region A3), and it is positioned with the A470 road to its north and the A487 road to its east, and has the town of Dolgellau towards the north-west.

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

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

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 26m of drop, based on the 395m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger map and the 369m bwlch spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website which was entitled the Interactive Coverage Map, however it was noted that the latter spot height was not centralised where interpolation would place the critical point of the bwlch. 

Extract from the Ordnance Survey 1:50,000 Landranger map

One of the resources recently available online is the mapping on the OS Maps website and the details for this hill were subsequently re-assessed against this mapping.  This is the replacement for OS Get-a-map and until recent times had contours at 5m intervals which were proving consistently more accurate compared to the 5m contours that sometimes appear on the Ordnance Survey 1:25,000 Explorer map and used to appear on the online Vector Map Local.  This mapping had bwlch contouring between 365m – 370m, with interpolation placing the height of the bwlch as an estimated c 366m, and when coupled with the 395m summit spot height these values gave this hill an estimated c 29m of drop.

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 395.1m summit height and a 364.9m bwlch height, with these values giving this hill 30.2m of drop, which is sufficient for it to be classified as a Trichant. 

 

The full details for the hill are: 

Group:  Cadair Idris 

Name:  Pen y Bwlch Coch 

OS 1:50,000 map:  124

Summit Height:  395.1m (LIDAR)                                                           

Summit Grid Reference:  SH 75190 15937 (LIDAR) 

Bwlch Height:  364.9m (LIDAR) 

Bwlch Grid Reference:  SH 75107 15780 (LIDAR) 

Drop:  30.2m (LIDAR) 

 

Myrddyn Phillips (September 2023)