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

 

Mynydd Melyn (SN 021 362) – Sub-Trichant addition

There has been confirmation of an addition 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 Mynydd Melyn (SN 021 362)

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 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 Melyn, 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 the A487 road to its north and minor roads to its west and east, and has the town of Abergwaun (Fishguard) towards the west.

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, as it was considered not to meet the criteria then used for this sub category.

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 24m of drop, based on the 307m summit spot height adjoined to a triangulation pillar that appears on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and the 283m bwlch spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage 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 confirmation of the addition of this hill to Sub-Trichant status is due to LIDAR analysis, resulting in a 307.3m summit height and a 283.2m bwlch height, with these values giving this hill 24.0m of drop, which is sufficient for it to be classified as a Sub-Trichant. 

 

The full details for the hill are: 

Group:  Mynydd Preseli 

Name:  Mynydd Melyn 

OS 1:50,000 map:  145

Summit Height:  307.3m (LIDAR)                                                           

Summit Grid Reference:  SN 02195 36233 (LIDAR) 

Bwlch Height:  283.2m (LIDAR) 

Bwlch Grid Reference:  SN 02621 36353 (LIDAR) 

Drop:  24.0m (LIDAR) 

 

Myrddyn Phillips (September 2024)