Mapping Mountains – Hill Reclassifications – Welsh Highlands – Uchafion Cymru

Llechwedd Diflas (SN 789 930) – 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 Llechwedd Diflas (SN 789 930)

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 Aled Williams and Myrddyn Phillips

The name the hill is listed by is Llechwedd Diflas and it is adjoined to the Pumlumon group of hills, which are situated in the northern part of South Wales (Region B, Sub-Region B1), and it is positioned with minor roads to its south south-west and east north-east, and has the village of Penffordd-las (Staylittle) towards the east.

When the initial P10 sub list was completed in June 2020 this hill was listed with an estimated c 10m of drop, based on the 514m summit spot height that appears on the contemporary Ordnance Survey 1:25,000 Explorer map, and an estimated c 504m bwlch height, based on interpolation of 5m contouring that appeared on online mapping. 

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 deletion of this hill from Welsh Highland Sub status is due to LIDAR analysis, resulting in a 513.4m summit height and a 503.8m bwlch height, with these values giving this hill 9.5m of drop, which is insufficient for it to be classified as a Welsh Highland Sub. 

 

The full details for the hill are: 

Group:  Pumlumon

Name:  Llechwedd Diflas

OS 1:50,000 map:  135

Summit Height:  513.4m (LIDAR)

Summit Grid Reference:  SN 78935 93043 (LIDAR)

Bwlch Height:  503.8m (LIDAR)

Bwlch Grid Reference:  SN 79224 92986 (LIDAR)   

Drop:  9.5m (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 (December 2023)