Mapping Mountains – Summit Relocations – The Welsh P15s

Cefn Gwrhyd (SN 737 096) 

There has been a Summit Relocation to a hill that is listed in the 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 summit relocation 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.  With an interpolated summit position later noted to an ancient cairn at SN 73735 09589. 

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. 

LIDAR summit image of Cefn Gwrhyd (SN 737 096)

LIDAR analysis gives the highest ground on this hill as 300.5m positioned at SN 73765 09682, and this position comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies to when the high point of the hill is positioned in a different field, to a different feature such as a conifer plantation, within a different map contour, a different point where a number of potential summit positions are within close proximity, when natural ground or the natural and intact summit is confirmed compared to a higher point such as a raised field boundary or covered reservoir that is considered a relatively recent man-made construct, or a relocation of approximately 100 metres or more in distance from either the position of a map spot height or from where the summit of the hill was previously thought to exist.

Therefore, the summit height produced by LIDAR analysis is 300.5m and this is positioned at SN 73765 09682, this position is not given a spot height on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, and is approximately 93 metres north north-eastward from where the ancient cairn is positioned. 

 

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 (New Position):  SN 73765 09682 (LIDAR) 

Bwlch Height:  283.1m (LIDAR) 

Bwlch Grid Reference:  SN 73543 09172 (LIDAR) 

Drop:  17.3m (LIDAR) 

 

Myrddyn Phillips (June 2024)