Mapping Mountains – Hill Reclassifications – Welsh Highlands – Uchafion Cymru

Carreg Gwalch (SH 642 552) – Welsh Highland Sub addition

There has been an addition 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 detail on contemporary maps produced from Ordnance Survey data and confirmed by subsequent LIDAR analysis and a Trimble GeoXH 6000 survey conducted by Aled Williams. 

LIDAR image of Carreg Gwalch (SH 642 552)

Carreg Gwalch (SH 642 552).  Photo: Aled Williams

The criteria for the list that this addition 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 Carreg Gwalch and it is adjoined to the Yr Wyddfa group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with the A4086 road to its north and the A498 to its south-east, and has the village of Capel Curig towards the east north-east.

This hill was not included as a P14 Sub in the original list of Welsh 500m P15s that later became known as Yr Uchafion and latterly as The Welsh Highlands – Uchafion Cymru, as with a 545m summit spot height and bwlch contouring between 530m – 540m that appear on the Ordnance Survey 1:25,000 Explorer map, interpolation suggested that it did not have sufficient drop to be considered for P14 500m Sub-Uchaf status.

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

Since the original compilation of this list there are now a number of interactive maps originated from Ordnance Survey data that are available online.  One of these is available on the Magic Maps website, and it is this map that gives this hill a summit spot height of 546m.

Extract from the Magic Maps website

Another resource now available online is the WalkLakes website which hosts an interactive map originated from the Ordnance Survey Open Data programme.  This map has many spot heights not on other publicly available Ordnance Survey maps and for this hill it also shows a 546m summit spot height which is positioned at SH 64236 55249.

Extract from the WalkLakes website

The details for this hill were also re-assessed when the OS Maps website became available online.  This is the replacement for OS Get-a-map and has contours at 5m intervals which are proving consistently more accurate compared to the 5m contours that sometimes appear on Ordnance Survey 1:25,000 Explorer maps and used to appear on the online Vector Map Local.  This mapping has an uppermost 545m ring contour and bwlch contouring between 530m – 535m, with interpolation giving an estimated bwlch height of c 532m.

Extract from the OS Maps website

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.  As this hill has now been surveyed with the Trimble GeoXH 6000, it is this result that is being prioritised.

Gathering data at the summit of Carreg Gwalch (SH 642 552).  Photo: Aled Williams

Gathering data at the bwlch of Carreg Gwalch (summit at SH 642 552).  Photo: Aled Williams

Therefore, the addition of this hill to Welsh Highland Sub status is due to detail on contemporary maps produced from Ordnance Survey data, and its status confirmed from subsequent LIDAR analysis and a Trimble GeoXH 6000 survey, resulting in a 546.0m summit height and a 531.2m bwlch height, with these values giving this hill 14.7m of drop, which is sufficient for it to be classified as a Welsh Highland Sub.

The full details for the hill are:

Group:  Yr Wyddfa

Name:  Carreg Gwalch

OS 1:50,000 map:  115

Summit Height:  546.0m (converted to OSGM15)

Summit Grid Reference:  SH 64238 55249

Bwlch Height:  531.2m (converted to OSGM15)

Bwlch Grid Reference:  SH 64229 55166 

  

Drop:  14.7m 

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

The Welsh 500m P15s (Yr Uchafion)

The Welsh 500m P15s (Yr Uchafion) – 500m Subs

The Welsh 500m P15s (Yr Uchafion) – 490m Subs

The Welsh 500m P15s (Yr Uchafion) – Double Subs

Aled Williams and Myrddyn Phillips (July 2020)