Mapping Mountains – Hill Reclassifications – Welsh Highlands – Uchafion Cymru

Esgair Pentanau (SN 846 703) – 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 LIDAR analysis and subsequently confirmed by a Trimble GeoXH 6000 survey; the former conducted by Aled Williams and the latter by Myrddyn Phillips and Aled Williams. 

Esgair Pentanau (SN 846 703)

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 Esgair Pentanau, and it is adjoined to the Carn yr Hyrddod group of hills, which are situated in the north-western part of South Wales (Region B, Sub-Region B1), and it is positioned with a minor road to its north-east and the B4343 road to its west, and has the town of Rhaeadr Gwy (Rhayader) towards the east.

The contemporary Ordnance Survey 1:25,000 Explorer map gives this hill a 503m summit spot height, with bwlch contouring between 490m – 500m.  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. 

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

When the initial P10 sub list was completed in June 2020 this hill was listed with 8.7m of drop based on analysis of the available 2m DSM LIDAR model.  When new Welsh LIDAR became available in April 2023 this hill was again analysed via LIDAR, now using the more accurate 1m DSM model. 

LIDAR image of Esgair Pentanau (SN 846 703)

LIDAR analysis using 1m DSM gives this hill over 10m of drop and therefore qualifying for Welsh Highland Sub status, and as this hill had now been surveyed with the Trimble GeoXH 6000, it is this result that is being prioritised for this hill. 

The Trimble GeoXH 6000 gathering data at the summit of Esgair Pentanau

The Trimble GeoXH 6000 gathering data at the bwlch of Esgair Pentanau

Therefore, the addition of this hill to Welsh Highland Sub status is due to LIDAR analysis, with confirmation via a subsequent Trimble GeoXH 6000 survey, resulting in a 504.2m summit height and a 493.2m bwlch height, with these values giving this hill 11.0m of drop, which is sufficient for it to be classified as a Welsh Highland Sub. 

 

The full details for the hill are: 

Group:  Carny yr Hyrddod

Name:  Esgair Pentanau

OS 1:50,000 map:  135, 136, 147

Summit Height:  504.2m (converted to OSGM15)

Summit Grid Reference:  SN 84648 70308

Bwlch Height:  493.2m (converted to OSGM15)

Bwlch Grid Reference:  SN 84472 69977   

Drop:  11.0m 

 

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 (July 2023)