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

 

Mynydd Deulyn (SH 756 608) – Sub-Trichant deletion

There has been a deletion from 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 Mynydd Deulyn (SH 756 608)

The criteria for the list that this deletion 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 Mynydd Deulyn and it is adjoined to the Carnedd Llywelyn group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned between Llyn Crafnant to its west and Llyn Geirionydd to its east, with the A5 road to its south, and the B5106 road, the Afon Conwy and the A470 road to its east, and has the village of Capel Curig towards the south-west and the town of Llanrwst 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 was not included in the Hills to be surveyed sub list that accompanied the main P30 list, as it was considered not to meet the criteria then used for this sub category. 

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

When the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated.  Its details were also re-examined 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 any other publicly available Ordnance Survey map. 

Extract from the interactive mapping on the OS Maps website

The details for this hill were also re-assessed when the interactive mapping on the OS Maps website became available online.  This is the replacement for OS Get-a-map and had contours at 5m intervals which were proving consistently more accurate compared to the 5m contours that sometimes appeared on Ordnance Survey 1:25,000 Explorer maps and the online Vector Map Local.  These re-assessments resulted in the hill being listed with an estimated c 20m of drop, based on its 382m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated c 362m bwlch height, based on interpolation of 5m contouring between 360m – 365m that appeared on the OS Maps website, resulting in the addition of this hill to Sub-Trichant status. 

LIDAR summit image of Mynydd Deulyn

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. 

LIDAR bwlch image of Mynydd Deulyn

Therefore, the deletion of this hill from Sub-Trichant status is due to LIDAR analysis, resulting in a 381.3m summit height and a 361.9m bwlch height, with these values giving this hill 19.4m of drop, which is insufficient for it to be classified as a Sub-Trichant. 

 

The full details for the hill are: 

Group:  Carnedd Llywelyn 

Name:  Mynydd Deulyn 

OS 1:50,000 map:  115

Summit Height:  381.3m (LIDAR)                                                           

Summit Grid Reference:  SH 75657 60898 (LIDAR) 

Bwlch Height:  361.9m (LIDAR) 

Bwlch Grid Reference:  SH 75753 61023 (LIDAR) 

Drop:  19.4m (LIDAR) 

 

Myrddyn Phillips (February 2025)