Mapping Mountains – Hill Reclassifications – Welsh Highlands – Uchafion Cymru

Pt. 686.3m (SH 736 136) – Welsh Highland Sub deletion 

There has been a deletion from 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 Pt. 686.3m (SH 736 136)

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 hill is being listed by the point (Pt. 686.3m) notation 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 A487 road to its south-east, and has the town of Dolgellau towards the north. 

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 an estimated c 10m of drop, based on the 2250ft (685.8m) summit height that appears on the Ordnance Survey series of Six-Inch maps and an estimated c 676m bwlch height, based on interpolation of 5m contouring that appeared on online mapping. 

Extract from the Ordnance Survey series of Six-Inch maps

When the sub list was updated with details from basic levelling surveys conducted by Myrddyn Phillips the details for this hill were re-evaluated and it was listed with 10.4m of drop, based on a basic levelling survey conducted on the 10.10.98 which gave this hill 34.0ft 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 deletion of this hill from Welsh Highland Sub status is due to LIDAR analysis, resulting in a 686.3m summit height and a 678.1m bwlch height, with these values giving this hill 8.2m of drop, which is insufficient for it to be classified as a Welsh Highland Sub. 

 

The full details for the hill are: 

Group:  Cadair Idris

Name:  Pt. 686.3m

OS 1:50,000 map:  124

Summit Height:  686.3m (LIDAR)

Summit Grid Reference:  SH 73642 13623 (LIDAR)

Bwlch Height:  678.1m (LIDAR)

Bwlch Grid Reference:  SH 73540 13543 (LIDAR)   

Drop:  8.2m (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 (October 2023)