Saturday, 25 March 2017

Mapping Mountains – Hill Reclassifications – Yr Uchafion


Fowler’s Arm Chair (SO 041 794) - Double Sub-Uchaf deletion

There has been a reclassification to 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 that have a minimum drop of 15m, the list is a joint compilation with Aled Williams, and details relating to this list were published on the Mapping Mountains site 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 reclassification of this hill affecting the Double Sub-Uchaf hills, with the criteria for inclusion to this sub category being Welsh hills at or above 490m and below 500m in height that have 14m or more and below 15m of drop.

Prior to analysis of LIDAR data by Aled the hill was listed with c 14m of drop based on an estimated summit height of c 491m and the 477m bwlch spot height that appears on the Ordnance Survey enlarged mapping hosted on the Geograph website.

The hill is situated in the Pegwn Mawr group with its Cardinal Hill being Brondre Fawr Hill (SO 041 783) and is placed in the Region of Mid and West Wales (Region B, Sub-Region B1), and is positioned between the small communities of Bwlch y Sarnau towards the south and Llanbadarn Fynydd towards the east south-east.

The hill can be accessed on public footpaths from a number of directions; however its summit is not on open access land, so if wanting to visit its high point permission to do so should be sought.

The name of the hill is Fowler’s Arm Chair and it is the first Double Sub-Uchaf to lose its status since the Yr Uchafion list was announced in November 2015, this 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 gives the hill the following details:


Fowler’s Arm Chair

Summit Height:  489.5m

Summit Grid Reference:  SO 04122 79426

Bwlch Height:  476.4m

Bwlch Grid Reference:  SO 04192 79062

Drop:  13.1m


Therefore, the 489.5m LIDAR data produced for the summit position at SO 04122 79426 and the 476.4m LIDAR data produced for the bwlch position at SO 04192 79062 gives this hill 13.1m of drop which along with its summit height is insufficient for it to retain its status as a Double Sub-Uchaf.

This now revises the listing of Yr Uchafion which will be updated accordingly and the hill is now deleted from the ranks of Double Sub-Uchaf, with this reclassification appearing in the appropriate Change Register.


The full details for the hill are:

Cardinal Hill:  Brondre Fawr Hill

Summit Height:  489.5m (LIDAR data)

Name:  Fowler’s Arm Chair

OS 1:50,000 map:  136, 147

Summit Grid Reference:  SO 04122 79426   

Drop:  13.1m (LIDAR data)


The reclassifications to the Double Sub-Uchaf category in Yr Uchafion / The Welsh 500m P15s reported on Mapping Mountains are ills of wales as follows:



DOUBLE SUB-UCHAF ADDITIONS




DOUBLE SUB-UCHAF DELETIONS

Fowler’s Arm Chair (SO 041 794) Double Sub-Uchaf deleted with 489.5m summit height and 13.1m drop




Myrddyn Phillips and Aled Williams (March 2017)

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