Mapping Mountains – Hill Reclassifications – Welsh Highlands – Uchafion Cymru

Cefn Blaen Merin (SN 812 810) – Welsh Highland P15 reclassified to Welsh Highland Sub 

There has been a reclassification 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 for the Welsh Highlands – Uchafion Cymru list authored by Aled Williams and Myrddyn Phillips. 

LIDAR image of Cefn Blaen Merin (SN 812 810)

The criteria for the list that this reclassification 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 Cefn Blaen Merin and 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 the A44 road to its north, the B4343 road and A4120 road to its west and a minor road to its south, and has the village of Ponterwyd towards the west.

This hill was not included in the list that later became known as the Welsh Highlands – Uchafion Cymru when the qualifying P15s were first compiled, however it was listed as a potential qualifying hill as it has an uppermost 550m ring contour estimated as c 552m in height and bwlch contouring between 530m - 540m with interpolation placing the height of the bwlch as an estimated c 537m. 

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

This hill was subsequently surveyed using a basic levelling staff on the 20^th November 2005 by Myrddyn Phillips, resulting in a 49½ft/15.1m drop value, which was sufficient for it to be classified in the main P15 list.  However, the margin of uncertainty applicable to the basic levelling method of surveying over the distance between bwlch and summit and the terrain of this hill is approximately +/- 0.5m.

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 reclassification of this hill to Welsh Highland Sub status is due to LIDAR analysis, resulting in a 552.9m summit height and a 538.1m bwlch height, with these values giving this hill 14.8m of drop, which is insufficient for it to be classified as a Welsh Highland P15. 

 

The full details for the hill are: 

Group:  Y Garn

Name:  Cefn Blaen Merin

OS 1:50,000 map:  135, 136

Summit Height:  552.9m (LIDAR)

Summit Grid Reference:  SN 81271 81064 (LIDAR)

Bwlch Height:  538.1m (LIDAR)

Bwlch Grid Reference:  SN 81424 81034 & SN 81425 81035 & SN 81427 81039 (LIDAR)   

Drop:  14.8m (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 (May 2023)