Tuesday, 31 January 2017

Mapping Mountains – Hill Reclassifications – Yr Uchafion

Cefn Onneu (SO 171 156) - Uchaf reclassified to 500m 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.  Details relating to this list were 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 500m Sub-Uchaf, with the criteria for this sub category being all Welsh hills at or above 500m in height that have 14m or more and below 15m of drop.

The hill is situated in the Bannau Brycheiniog (Brecon Beacons) group of hills with its Cardinal Hill being Pen y Fan (SO 012 215) and is placed in the Region of South Wales (C-2).  The hill is situated between the villages of Llangynidr to its north north-west, Cendl (Beaufort) to its south and Llangatwg to its east north-east.

The hill was listed with c 15m of drop which is the minimum drop value for inclusion as an Uchaf, with a c 530m summit based on a small uppermost 530m ring contour on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps, and an estimated bwlch height of c 515m based on bwlch contouring between 510m – 520m.

The name of the hill is Cefn Onneu and it can be easily accessed from its west as the B 4560 passes within 0.7km of its summit, and its reclassification from an Uchaf to a 500m Sub-Uchaf is due to the 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:

Cefn Onneu

Summit Height:  530.0m

Summit Grid Reference:  SO 17112 15692

Bwlch Height:  515.6m

Bwlch Grid Reference:  SO 16549 15819

Drop:  14.4m

Therefore, the 530.0m LIDAR data produced for the summit position at SO 17112 15692 and the 515.6m LIDAR data produced for the bwlch position at SO 16549 15819 gives this hill 14.4m of drop which is insufficient for it to retain its Uchaf status as its drop is below the required minimum of 15m.

The full details for the hill are:

Cardinal Hill:  Pen y Fan

Summit Height:  530.0m (LIDAR data)

Name:  Cefn Onneu

OS 1:50,000 map:  161

Summit Grid Reference:  SO 17112 15692 
Drop:  14.4m (LIDAR data)

This now brings the overall total for Yr Uchafion / The Welsh 500m P15s to 630 hills and the overall total for the 500m Sub-Uchaf category to 25.

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



Cefn Onneu (LIDAR data) (SO 171 156) Uchaf reclassified to 500m Sub-Uchaf with 14.4m of drop


Myrddyn Phillips and Aled Williams (January 2017)

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