Mapping Mountains – Hill Reclassifications – The Welsh P15s

 

Cefn Gwrhyd (SN 737 096) – Welsh P15 addition 

There has been an addition to the list of The Welsh P15s, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Cefn Gwrhyd (SN 737 096)

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

The Welsh P15s – Welsh hills with 15m minimum drop, irrespective of their height, with an accompanying sub list entitled the Welsh Sub-P15s, with the criteria for this sub category being all Welsh hills with 14m or more and below 15m of drop.  The list is authored by Myrddyn Phillips, with the Introduction to the list appearing on Mapping Mountains on the 10^th May 2019. 

The Welsh P15s by Myrddyn Phillips

The name the hill is listed by is Cefn Gwrhyd, and it is adjoined to the Mynydd Du group of hills, which are situated in the southern part of South Wales (Region B, Sub-Region B5), and it is positioned with the A4068 road to its north-east, the A474 road to its west, the A4067 road to its south-east and a minor road to its immediate east, and has the community of Y Gurnos towards the east.

When the listing that became known as The Welsh P15s was being compiled, this hill was not included as with a 291m spot height in the vicinity of its summit and bwlch contouring between 280m – 290m that appear on the contemporary Ordnance Survey 1:25,000 Explorer map, it was judged not to meet the criterion for the main P15 or the accompanying P14 sub list. 

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

One of the mapping resources 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 maps and for this hill a 300m summit spot height is given.

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.

Therefore, the addition of this hill to Welsh P15 status is due to LIDAR analysis, resulting in a 300.5m summit height and a 283.1m bwlch height, with these values giving this hill 17.3m of drop, which is sufficient for it to be included in the main list of The Welsh P15s. 

 

The full details for the hill are: 

Group:  Mynydd Du 

Name:  Cefn Gwrhyd 

OS 1:50,000 map:  160

Summit Height:  300.5m (LIDAR)                                                           

Summit Grid Reference:  SN 73765 09682 (LIDAR) 

Bwlch Height:  283.1m (LIDAR) 

Bwlch Grid Reference:  SN 73543 09172 (LIDAR) 

Drop:  17.3m (LIDAR) 

 

Myrddyn Phillips (May 2024)