Saturday, 24 December 2016

Mapping Mountains – Hill Reclassifications – Y Pedwarau

Craig Rhiw Berfa (SS 945 906) - 390m Double Sub-Pedwar deletion

There has been a deletion from the 390m Double Sub-Pedwar list by analysis of LIDAR data by Aled Williams.  The 390m Double Sub-Pedwarau are the hills at or above 390m and below 400m in height with a drop between 20m and below 30m, with the 390m Sub-Pedwarau being the hills within the same height band and with a minimum 30m of drop.

The hill is situated in the group of hills known as the Y Cymoedd with its Cardinal Hill being Werfa (SS 912 947) and is placed in the Region of South Wales (C-2).  The hill is positioned between the village of Cwm Ogwr (Ogmore Vale) in the valley of Cwm Ogwr Fawr to its west and the village of Gilfach Goch in the valley of Cwm Ogwr Fach to its east south-east, and it can be accessed from the west on a track that follows the course of the Nant Cwm-y-fuwch before the upper northerly slopes of the hill are ascended.

The name of the hill is Craig Rhiw Berfa and it was listed as a 390m Double Sub-Pedwar with a drop of c 21m based on the 399m summit spot height and a bwlch height of c 378m estimated from contour interpolation on the Ordnance Survey 1:25,000 Explorer map.  The hill was not included in the May 2013 Europeaklist publication and was later added via an announcement on the Mapping Mountains site on 28.02.14.

As Aled was analysing other hills in the vicinity against LIDAR data, he did likewise with Craig Rhiw Berfa.  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:

Craig Rhiw Berfa

Summit Height:  397.2m

Summit Grid Reference:  SS 94593 90610

Bwlch Height:  378.4m

Bwlch Grid Reference:  SS 94961 90750

Drop:  18.8m

Therefore, the 397.2m LIDAR data produced for the summit position at SS 94593 90610 and the 378.4m LIDAR data produced for the bwlch position at SS 94961 90750 is insufficient for this hill to retain its 390m Double Sub-Pedwar status as it only has 18.8m of drop, and therefore Craig Rhiw Berfa is taken out of the listing of 390m Double Sub-Pedwar hills and the list will be updated accordingly.

The full details for the hill are:

Cardinal Hill:  Werfa

Summit Height:  397.2m (LIDAR data)

Name:  Craig Rhiw Berfa

OS 1:50,000 map:  170

Summit Grid Reference:  SS 94593 90610

Drop:  18.8m (LIDAR data)

Therefore, Craig Rhiw Berfa is the first hill to be deleted from the 390m Double Sub-Pedwar listing from analysis of LIDAR data and the list of Y Pedwarau will be updated accordingly.  The list of Pedwar hills is available from the Haroldstreet (January 2014) website and amendments to the list since this publication have been subsequently reported on the Mapping Mountains site.

Myrddyn Phillips and Aled Williams (December 2016)

No comments: