Sunday, 21 May 2017

Mapping Mountains – Hill Reclassifications – Yr Uchafion



Banc Steffan (SN 833 700) – 500m Sub-Uchaf deletion

There has been a deletion from the listing of Yr Uchafion instigated from analysis of LIDAR data 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 that have a minimum drop of 15m, the list is a joint compilation between Myrddyn Phillips and Aled Williams with the introduction to the list being published on Mapping Mountains in November 2015.

Accompanying the main Yr Uchafion list are three sub lists; 500m Sub-Uchaf, 490m Sub-Uchaf and the Double Sub-Uchaf categories, 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 analysis of LIDAR data the 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 the land where Banc Steffan is situated has three individual summits, with each separated by a bwlch, it is wise to list their details from north to south that appear on the Ordnance Survey 1:25,000 Explorer map:


Summit 1 – Cnapyn Drawsffos (SN 83443 70638) 549m

Bwlch 1 – 530m – 540m (SN 83371 70383)

Summit 2 – Banc Steffan (SN 83359 70024) no spot height with 540m uppermost contour ring

Bwlch 2 – 530m – 540m (SN 83222 69403)

Summit 3 – Cefn Ffosyrewig (SN 83242 69234) 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 data gives Cnapyn Drawsffos as higher than Banc Steffan, and Banc Steffan higher than Cefn Ffosyrewig, it is Banc Steffan that would have been listed as a 500m Sub-Uchaf.

The hill is situated in the Elenydd group of hills with its Cardinal Hill being Carn yr Hyrddod (SN 790 704) and is placed in the Region of Mid and West Wales (Region B, Sub-Region B2), and in Welsh terms the hill is a long way away 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 possibly the best option.  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 a bit wild.

The name of the hill is Banc Steffan and its deletion from the 500m Sub-Uchaf category is due to the analysis of LIDAR data by Aled.  LIDAR (Light Detection & Ranging) is highly accurate height data that is now freely available for much of England and Wales.

Aled’s analysis of LIDAR data distinguished Banc Steffan to be higher than Cefn Ffosyrewig and gives the hill the following details:


Banc Steffan

Summit Height:  548.0m

Summit Grid Reference:  SN 83359 70024

Bwlch Height:  534.2m

Bwlch Grid Reference:  SN 83371 70383

Drop:  13.8m


Therefore, the 548.0m LIDAR data produced for the summit position at SN 83359 70024 and the 534.2m LIDAR data produced for the bwlch position at SN 83371 70383 gives this hill 13.8m of drop which is insufficient for it to retain its status as a 500m Sub-Uchaf.


The full details for the hill are:

Cardinal Hill:  Carn yr Hyrddod

Summit Height:  548.0m (LIDAR data)

Name:  Banc Steffan

OS 1:50,000 map:  135, 136, 147

Summit Grid Reference:  SN 83359 70024 
  
Drop:  13.8m (LIDAR data)


The overall total for Yr Uchafion / The Welsh 500m P15s remains at 631 hills with the total for the 500m Sub-Uchaf category remains at 25.  This figure remains at it was prior to this hill's deletion as the hill was missed from this sub category when the Introduction to the list was published on Mapping Mountains in November 2015.

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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