Mapping Mountains – Hill Reclassifications – Welsh Highlands – Uchafion Cymru

Pen y Bwlch (SN 929 669) – 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 Pen y Bwlch (SN 929 669)

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 Pen y Bwlch it is adjoined to the Y Garn group of hills, which are situated in the northern part of South Wales (Region B, Sub-Region B1), and it is positioned with a minor road to its north-east and west, and the B4518 road to its south-east, and has the town of Rhaeadr Gwy towards the east north-east.

This hill was originally listed as a sub due to a basic levelling survey conducted by Myrddyn Phillips on the 17.08.05 resulting in a 47ft (14.3m) drop value, with the summit height listed as an estimated c 500m, based on interpolation of the small uppermost 500m ring contour that appears on the contemporary Ordnance Survey 1:25,000 Explorer map. 

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

When the initial P10 sub list was completed in June 2020 this hill was included as a sub with an accompanying note stating:

LIDAR 2m DSM bwlch by AW. BLS by MP on 17/08/2005 giving 47ft (14.3m). Adding the BLS drop result to the bwlch height determined via LIDAR analysis gives a summit height of 500.1m. Summit height is inconsistent on OS maps, giving a range of 499m to 500m. Partial coverage LIDAR 2m DSM by AW gives 498.1m summit-area high point at SN 92831 66910. The OS 6" Map (1888) gives a 1633ft (497.7m) summit-area high point at SN 93067 66918.

However, it was not until full LIDAR coverage 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 499.6m summit height and a 485.6m bwlch height, with these values giving this hill 14.05m of drop, with its height being insufficient for it to be classified as a Welsh Highland Sub. 

 

The full details for the hill are: 

Group:  Y Garn

Name:  Pen y Bwlch

OS 1:50,000 map:  136, 147

Summit Height:  499.6m (LIDAR)

Summit Grid Reference:  SN 92901 66972 (LIDAR)

Bwlch Height:  485.6m (LIDAR)

Bwlch Grid Reference:  SN 92677 66989 (LIDAR)   

Drop:  14.05m (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)