Wednesday, 25 January 2017

Mapping Mountains – Hill Reclassifications – Y Pedwarau

The two tops of Cefn Bach have now been surveyed with the Trimble GeoXH 6000, resulting in:

Surveyed on 18.08.15: 389.392m at SO 00293 37291

Surveyed on 30.12.18:  389.391m at SO 00470 38742

With 1mm difference in height the Trimble is unable to split these summits, therefore they remain deleted from 390m Double Sub-Pedwar status and are reinstated as twin Trichant tops, the post below remains as originally written for historic merit.

Cefn Bach (SO 004 387) - 390m Double Sub-Pedwar deletion

There has been a deletion of a 390m Double Sub-Pedwar by analysis of LIDAR data by Aled Williams.  The 390m Double Sub-Pedwarau is one of three categories of sub hills that accompany the main Y Pedwarau list, with the criteria for 390m Double Sub-Pedwar status being all Welsh hills at or above 390m and below 400m in height with 20m or more and below 30m of drop.

The hill is situated in the group of hills known as Mynydd Epynt with its Cardinal Hill being Clepyn Melyn (SN 961 464) and is placed in the Region of Mid and West Wales (B-2).  The hill is positioned between the small communities of Upper Chapel to the north, Lower Chapel to the south-east and Merthyr Cynog to the south-west, and between the river valleys of the Ysgir Fawr to the west and the Honddu to the east.  A narrow lane passes to the north of this hill and a public footpath leads from this to just below the summit.

The name of the hill is Cefn Bach and it had been listed in the Y Pedwarau Europeaklist booklet with c 22m of drop based on its 391m summit spot height at SO 00375 38722 and an estimated bwlch height of c 369m based on bwlch contouring between 360m – 370m.  This hill was listed as a 390m Double Sub-Pedwar in deference to its 391m map heighted twin summit which was listed as the 390m Sub-Pedwar with its 391m spot height at SO 00284 37297, these two hills are aligned in a north – south direction, with the southerly hill being listed with 55m of drop based on a 336m bwlch spot height.

Since the Europeaklist publication of the Y Pedwarau the southerly of these two 391m map heighted hills has been surveyed with the Trimble GeoXH 6000 resulting in a 389.4m (converted to OSGM15) summit height at SO 00293 37291 and a 335.0m (converted to OSGM15) bwlch height at SO 00287 36949.  However, the northerly summit remained un-Trimbled and the relative height of each summit was only ascertained from analysis of LIDAR data.

As Aled was analysing other hills in the vicinity against LIDAR data, he did likewise with the two Cefn Bach hills.  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:  389.2m

Summit Grid Reference:  SO 00471 38745

Bwlch Height:  368.9m

Bwlch Grid Reference:  SO 00075 38322

Drop:  20.3m

Therefore, the 389.2m LIDAR data produced for the summit position at SO 00471 38745 and the 368.9m LIDAR data produced for the bwlch position at SO 00075 38322 is insufficient for this hill to retain its 390m Double Sub-Pedwar status as its summit is below the required height threshold.

The full details for the hill are:

Cardinal Hill:  Clepyn Melyn

Summit Height:  389.2m (LIDAR data)

Name:  Cefn Bach

OS 1:50,000 map:  160

Summit Grid Reference:  SO 00471 38745

Drop:  20.3m (LIDAR data)

This now brings the overall total for the 390m Double Sub-Pedwarau to 27 hills with 13 additions and two deletions to this sub category of hill since publication of the list by Europeaklist in May 2013.  The hill will be taken out of the 390m Double Sub-Pedwar list in forthcoming publications of the Y Pedwarau.  The list of Pedwar hills is available from the Haroldstreet website (January 2014) with all subsequent changes available via the Mapping Mountains site.

The additions, reclassifications and deletions to the 390m Double Sub-Pedwarau since the 1st edition of the Y Pedwarau was published by Europeaklist are as follows:



Cefn Bach (SO 004 387) 389.2m summit and 20.3m drop

Cefn Bach (SO 004 387) the deleted 390m Double Sub-Pedwar

Myrddyn Phillips and Aled Williams (January 2017)

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