Thursday, 22 December 2016

Mapping Mountains – Hill Reclassifications – Y Pedwarau

Cefn Bach (SO 208 038) - 400m Sub-Pedwar addition

There has been a new 400m Sub-Pedwar added to the list by analysis of LIDAR data by Aled Williams.  The 400m Sub-Pedwarau are the Welsh hills at or above 400m and below 500m in height with a drop between 20m and below 30m.

The hill is situated in the group of hills known as the Y Cymoedd with its Cardinal Hill being Mynydd Carn y Cefn (SO 187 085) and is placed in the Region of South Wales (C-2).  The hill is positioned above the town of Abertyleri (Abertillery) to its east and between the river valleys of the Afon Ebwy (Ebbw River) to the west and the Afon Ebwy Fach (Ebbw Fach River) to the east, and can be easily accessed from a track from its south, and from the continuation of the track from the west.

The name of the hill is Cefn Bach and prior to the analysis of LIDAR data the hill was catalogued as having only 7m of drop based on a 416m summit spot height at SO 20738 04263 and a 409m bwlch spot height at SO 20369 04523, with the latter spot height appearing on the Ordnance Survey enlarged mapping on the Geograph website.  The contouring near the area of the bwlch is different between the Ordnance Survey 1:25,000 Explorer map and the enlarged Geograph map and the summit position indicated by LIDAR is on the edge of the uppermost contour on current 1:25,000 maps, with the contouring disappearing at this same position on the enlarged Geograph map, indicating that the present day summit is the relic of mine spoil, this is confirmed when analysing older maps.

As Aled was analysing other hills in the vicinity against LIDAR data, he did likewise with Cefn Bach.  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 Bach

Summit Height:  427.2m

Summit Grid Reference:  SO 20819 03887

Bwlch Height:  406.2m

Bwlch Grid Reference:  SO 20893 03917

Drop:  21.0m

Therefore, the 427.2m LIDAR data produced for the summit position at SO 20819 03887 and the 406.2m LIDAR data produced for the bwlch position at SO 20893 03917 is sufficient for this hill to be reclassified to a 400m Sub-Pedwar with 21.0m of drop, and therefore Cefn Bach is included in the listing of 400m Sub-Pedwar hills and the list of Y Pedwarau will be updated accordingly.  The list of Pedwar hills is available from the Haroldstreet website (January 2014) with all subsequent changes available via the Mapping Mountains site.

The full details for the hill are:

Cardinal Hill:  Mynydd Carn y Cefn

Summit Height:  427.2m (LIDAR data)

Name:  Cefn Bach

OS 1:50,000 map:  171

Summit Grid Reference:  SO 20819 03887

Drop:  21.0m (LIDAR data)

The list of additions, reclassifications and deletions from the 400m Sub-Pedwar list since the 1st edition of the Y Pedwarau was published by Europeaklist are as follows:


Cefn Bach (LIDAR data) (SO 208 038) 21.0m drop



Myrddyn Phillips and Aled Williams (December 2016)

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