Mapping Mountains – Hill Reclassifications – Welsh Highlands – Uchafion Cymru

Y Ddau Faen Llwyd (SH 804 310) – Welsh Highland Sub deletion 

There has been a deletion to the listing of the Welsh Highlands – Uchafion Cymru, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Aled Williams. 

LIDAR image of Y Ddau Faen Llwyd (SH 804 310)

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

Welsh Highlands – Uchafion Cymru – Welsh hills at or above 500m in height with 15m minimum drop, with an accompanying sub list entitled the Welsh Highland Subs, the criteria for which is all Welsh hills at or above 500m in height with 10m or more and below 15m of drop.  This list is authored by Myrddyn Phillips and Aled Williams with the Introduction to the list published on Mapping Mountains in November 2015 and the latest update relating to the list published on Mapping Mountains in January 2023.

Welsh Highlands - Uchafion Cymru by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Y Ddau Faen Llwyd and it is adjoined to the Arenig Fawr group of hills, which are situated in the central part of North Wales (Region A, Sub-Region A2), and it is positioned with a minor road to its north-east and south-west, and has the village of Llanuwchllyn towards the east. 

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

When the initial P10 sub list was completed in June 2020 this hill was listed with 10m of drop, based on the 537m summit spot height that appears on online mapping, including the interactive map hosted on the WalkLakes website and a 527m bwlch height, based on the 1730ft (527.3m) levelled height that appears on the Ordnance Survey series of Six-Inch maps.  Therefore, it was included as a Welsh Highland Sub when the drop value of the subs was agreed upon and revised in July 2020. 

Extract from the interactive mapping hosted on the WalkLakes website

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. 

Extract from the Ordnance Survey series of Six-Inch maps

Therefore, the deletion of this hill from Welsh Highland Sub status is due to LIDAR analysis, resulting in a 537.3m summit height and a 527.6m bwlch height, with these values giving this hill 9.7m of drop, which is insufficient for it to be classified as a Welsh Highland Sub. 

 

The full details for the hill are: 

Group:  Arenig Fawr

Name:  Y Ddau Faen Llwyd

OS 1:50,000 map:  124, 125

Summit Height:  537.3m (LIDAR)

Summit Grid Reference:  SH 80456 31074 (LIDAR)

Bwlch Height:  527.6m (LIDAR)

Bwlch Grid Reference:  SH 80534 31223 (LIDAR)   

Drop:  9.7m (LIDAR) 

 

For the additions, deletions and reclassifications to the Welsh Highlands – Uchafion Cymru reported on Mapping Mountains please consult the following Change Registers:

 

Welsh Highland P15s

 

Welsh Highland Subs

 

Aled Williams and Myrddyn Phillips (August 2023)