Mapping Mountains – Summit Relocations – The Welsh P15s

 

Cae Plu (SN 562 035) 

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 Cae Plu (SN 562 035)

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 now listed by is Cae Plu, and this was derived from the Tithe map, and it is adjoined to the Mynydd Sylen group of hills, which are situated in the southern part of South Wales (Region B, Sub-Region B5), and it is positioned with a minor road to its north, the A4138 road to its south and the M4 motorway to its east, and has the town of Llanelli towards the south-west.

When the listing that became known as The Welsh P15s was being compiled, this hill was included in the accompanying sub list with an estimated c 14m of drop, based on the 106m summit spot height that was positioned at SN 56242 03523 and which appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map, and an estimated c 92m bwlch height based on interpolation of 5m contouring between 90m – 95m. 

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

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 analysis gives the highest ground on this hill as 107.6m positioned at SN 56243 03507.  However, this is to the top of a raised field boundary and protocols dictate that as this is deemed a relatively recent man-made construct such ground is discounted from the height of a hill. 

LIDAR summit image of Cae Plu (SN 562 035)

The height produced by LIDAR analysis to the natural summit of this hill is 106.65m and is positioned at SN 56249 03517, and this comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies when the high point of the hill is found to be positioned; in a different field, to a different feature such as in a conifer plantation,  within a different map contour, to a different point where a number of potential summit positions are within close proximity, when natural ground or the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary or covered reservoir that is judged to be 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 106.65m and is positioned at SN 56249 03517, this position is relatively close to where the 106m spot height appeared, and is approximately 10 metres north-eastward from the high point of the raised field boundary. 

 

The full details for the hill are: 

Group:  Mynydd Sylen 

Name:  Cae Plu 

OS 1:50,000 map:  159

Summit Height:  106.65m (LIDAR)                                                           

Summit Grid Reference (New Position):  SN 56249 03517 (LIDAR)                                                  

Bwlch Height:  91.5m (LIDAR) 

Bwlch Grid Reference:  SN 56274 03613 (LIDAR) 

Drop:  15.15m (LIDAR) 

 

Myrddyn Phillips (February 2025)