Sunday, 21 May 2017

Mapping Mountains – Hill Reclassifications – Welsh Highlands - Uchafion Cymru

Cefn Ffos yr Ewig (SN 832 692) – 500m Sub-Uchaf deletion

There has been a deletion from the listing of Yr Uchafion instigated by LIDAR analysis conducted by Aled Williams.  Yr Uchafion is the draft title for a list of the Welsh 500m P15s that takes in all hills in Wales at or above 500m in height with 15m minimum drop.  The list is a joint compilation between Myrddyn Phillips and Aled Williams with the Introduction to the list published on Mapping Mountains in November 2015.

LIDAR image of Cefn Ffos yr Ewig (SN 832 692)

Accompanying the main Yr Uchafion list are three categories of sub lists; 500m Sub-Uchaf, 490m Sub-Uchaf and Double Sub-Uchaf, with the deletion of this hill affecting the 500m Sub-Uchaf category, with the criteria for inclusion to this sub category being all Welsh hills at or above 500m in height that have 14m or more and below 15m of drop.

Prior to LIDAR analysis this hill was listed with 14m of drop which was sufficient for it to be included as a 500m Sub-Uchaf.  This drop value was based on a basic levelling survey (BLS) conducted by Myrddyn Phillips. 

To explain the process of the BLS and as Cefn yr Ewig has two adjacent summits, with each separated by a bwlch, the Ordnance Survey 1:25,000 Explorer map details are given below and listed from north to south:

Summit 1 – Cnapyn Drawsffos (SN 83443 70639) 549m

Bwlch 1 – 530m – 540m (SN 83373 70381)

Summit 2 – Banc Steffan (SN 83357 70017) no spot height with 540m uppermost contour ring

Bwlch 2 – 530m – 540m (SN 83223 69404)

Summit 3 – Cefn Ffos yr Ewig (SN 83243 69235) 549m

The BLS resulted in 46ft 6˝ (14.2m) of drop and was conducted from Bwlch 1 to summit 1 (Cnapyn Drawsffos) and as Summit 1 and Summit 3 both have 549m spot heights the BLS survey meant that whichever was lower in height would qualify as a 500m Sub-Uchaf.  However, as LIDAR gives Cnapyn Drawsffos as higher than Cefn Ffos yr Ewig, and both hills higher than Banc Steffan, it was Cefn Ffos yr Ewig that was listed as a 500m Sub-Uchaf.

Extract from the Ordnance Survey 1:25,00 Explorer map

Cefn Ffos yr Ewig is situated in the Elenydd group with its Cardinal Hill being Carn yr Hyrddod (SN 790 704) and is placed in Mid and West Wales (Region B, Sub-Region B2), and for Wales it is a relatively remote hill and a long way from any small community.

The hill is one of the remotest situated from any paved public road in Wales, therefore an ascent is likely to be a long affair, with an ascent from the east north-east following the old Monks Trod being one of the best options.  However, much of the higher Elenydd is open country and has enjoyed unrestricted access for many years and an ascent from most directions will be fulfilling, albeit very wild.

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 bwlch image for Cefn Ffos yr Ewig

The deletion of this hill from 500m Sub-Uchaf status is due to LIDAR analysis, resulting in a 547.5m summit height and a 534.3m bwlch height, with these values giving this hill 13.3m of drop which is insufficient for 500m Sub-Uchaf status.

The full details for the hill are:

Cardinal Hill:  Carn yr Hyrddod

Name:  Cefn Ffos yr Ewig

OS 1:50,000 map:  135, 136, 147

Summit Height:  547.5m (LIDAR)

Summit Grid Reference:  SN 83243 69235 (LIDAR) 
Bwlch Height:  534.3m (LIDAR)

Bwlch Grid Reference:  SN 83373 70381 (LIDAR)

Drop:  13.3m (LIDAR)

For the additions, reclassifications and deletions to Yr Uchafion / The Welsh 500m P15s reported on Mapping Mountains please consult the following Change Registers:

Myrddyn Phillips and Aled Williams (May 2017)

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