Wednesday, 19 July 2017

Mapping Mountains – Hill Reclassifications – Yr Uchafion

Carreg yr Ast (SN 877 591) – 500m Sub-Uchaf addition

There has been an addition 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 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 addition 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 not classified as its estimated drop was c 13m based on its 579m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and an estimated bwlch height of c 566m based on bwlch contouring between 560m – 570m.

The hill is situated in the Elenydd group of hills with its Cardinal Hill being Drygarn Fawr (SN 862 584) 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 a part of designated open access land and for those wishing to visit it can be combined with Drygarn Fawr and Gorllwyn which gives a rewarding walk on the high summits of the Elenydd, with easiest access from the north.

The name of the hill is Carreg yr Ast and its addition to 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 gives the hill the following details:

Carreg yr Ast

Summit Height:  579.2m

Summit Grid Reference:  SN 87717 59184

Bwlch Height:  564.3m

Bwlch Grid Reference:  SN 87743 58937

Drop:  14.9m

Therefore, the 579.2m (579.23m) LIDAR data produced for the summit position at SN 87717 59184 and the 564.3m (564.29m) LIDAR data produced for the bwlch position at SN 87743 58937 gives this hill 14.9m (14.94m) of drop which is sufficient for it to be classified as 500m Sub-Uchaf.

The full details for the hill are:

Cardinal Hill:  Drygarn Fawr

Summit Height:  579.2m (LIDAR data)

Name:  Carreg yr Ast

OS 1:50,000 map:  147

Summit Grid Reference:  SN 87717 59184  
Drop:  14.9m (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 increasing by one to 26 hills.

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 (July 2017)

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