Monday, 13 March 2017

Mapping Mountains – Hill Reclassifications – Yr Uchafion


Pt. 499.1m (SN 863 760) - Uchaf reclassified to 490m Sub-Uchaf

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, with the details relating to this list being published on the Mapping Mountains site in November 2015.

The listing of Yr Uchafion includes three sub lists; the 500m Sub-Uchaf, 490m Sub-Uchaf and the Double Sub-Uchaf category.  The reclassification of this hill is from Uchaf to 490m Sub-Uchaf, this sub category takes in the hills at or above 490m and below 500m in height that have 20m or more and below 30m of drop.

The hill is situated in the Elenydd group of hills with its Cardinal Hill being Draws Drum (SN 790 811) and is placed in the Region of Mid and West Wales (Region B, Sub-Region B2).  The hill is situated with the small community of Llangurig to the north-east and Cwmystwyth to the west south-west and is positioned directly above and to the north of the narrow mountain road that heads north-westward from Rhaeadr Gwy (Rhayader).

The hill can be accessed relatively easily from the minor road to its west south-west, from where a public footpath is indicated on Ordnance Survey maps heading up the stream valley to the hill’s west, from here the ascent is on relatively easy grass to a flat topped summit.

The hill was previously listed as an Uchaf and given an estimated height of c 500m based on the flatness of its summit area in relation to the small uppermost 500m contour ring that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

The name of the hill is currently being listed by the point (Pt. 499.1m) notation until this list is published and its reclassification from Uchaf to 490m Sub-Uchaf is due to analysis of LIDAR data by Aled Williams.  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:


Pt. 499.1m

Summit Height:  499.1m

Summit Grid Reference:  SN 86343 76073

Bwlch Height:  471.0m

Bwlch Grid Reference:  SN 86323 76358

Drop:  28.1m


Therefore, the 499.1m LIDAR data produced for the summit position at SN 86343 76073 and the 471.0m LIDAR data produced for the bwlch position at SN 86323 76358 gives this hill 28.1m of drop, which is in good accordance with the value produced for this hill when surveyed by John Barnard, Graham Jackson, David Purchase and myself in June 2008 using a level and staff resulting in a drop of 27.9m.  Therefore the summit height of this hill is insufficient for it to retain its Uchaf status. 


The full details for the hill are:

Cardinal Hill:  Draws Drum

Summit Height:  499.1m (LIDAR data)

Name:  Pt. 499.1m

OS 1:50,000 map:  135, 136, 147

Summit Grid Reference:  SN 86343 76073 
  
Drop:  27.9m (line survey)


This now brings the overall total for Yr Uchafion / The Welsh 500m P15s to 628 hills with the overall total for the 500m Sub-Uchaf category remaining at 26, and the 490m Sub-Uchaf total increasing by one to 62.

The additions, reclassifications and deletions to Yr Uchafion / The Welsh 500m P15s reported on Mapping Mountains are ills of wales as follows:



UCHAF ADDITIONS









UCHAF RECLASSIFICATIONS TO 500m SUB-UCHAF









UCHAF RECLASSIFICATIONS TO 490m SUB-UCHAF

Pt. 499.1m (SN 863 760) Uchaf reclassified to 490m Sub-Uchaf with 499.1m summit height




UCHAF DELETIONS






Myrddyn Phillips and Aled Williams (March 2017)





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