Wednesday, 23 September 2015

Mapping Mountains – Summit Relocations – Y Pedwarau and Y Trichant


Cefn Bach (SO 002 372) 

There has been a de-twinning of summits that is being detailed as a Summit Relocation initiated by a survey with the Trimble GeoXH 6000 in conjunction with LIDAR data analysed by Aled Williams, with this hill listed in both the Y Pedwarau and the Y Trichant, with the following details being retrospective as the Trimble survey that partly resulted in this summit relocation was conducted on 18th August 2015.

The Y Pedwarau comprise the 400m hills of Wales that have a minimum 30m of drop, accompanying the main P30 list are also a number of sub lists.  Whilst the Y Trichant comprise the 300m hills of Wales that have a minimum 30m of drop with an accompanying sub list entitled the Sub-Trichant.

The hill has twin map heighted 391m summits which are orientated north to south, both are a part of the hill named as Cefn Bach and therefore each summit is listed by this name.  Prior to the survey with the Trimble and the analysis of LIDAR data the southerly summit at SO 002 372 was prioritised and listed as a 390m Sub-Pedwar and a Trichant with 55m of drop, whilst the northerly summit at SO 003 387 was listed as a 390m Double Sub-Pedwar and Sub-Trichant with c 22m of drop.   

The survey with the Trimble GeoXH 6000 was conducted in the southern hills of Mynydd Epynt on a fine and bright day during a circuit of three hills, with the hill positioned between the small communities of Merthyr Cynog to the west and Lower Chapel to the east south-east. 

The two summits are easily accessed from a narrow lane to their south where one car can be squeezed onto the grass verge.  This ascent requires a there and back walk, alternatively a similar there and back walk can be taken from a lane to the north-west of the northerly summit.

Unfortunately there was only sufficient time to survey the southerly of these two summits with the Trimble GeoXH 6000, and therefore an accurate value for the northerly summit awaited analysis of LIDAR data.



Aled’s analysis of LIDAR data for the northerly summit of Cefn Bach gives 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




The Trimble survey and Aled's analysis of LIDAR data for the southerly summit of Cefn Bach gives the following details:




Cefn Bach

Summit Height:  389.4m

Summit Grid Reference:  SO 00293 37291

Bwlch Height:  335.0m

Bwlch Grid Reference:  SO 00293 36953

Drop:  54.4m



Therefore, as both hills are under 390m in height their status within the Y Pedwarau is deleted.  Whilst their status within the Y Trichant is now confirmed and remains as it was. 


The full details for the northerly hill are:


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)






The full details for the southerly hill are:


Cardinal Hill:  Clepyn Melyn

Summit Height:  389.4m (converted to OSGM15) (Trimble and LIDAR data)

Name:  Cefn Bach

OS 1:50,000 map:  160

Summit Grid Reference:  SO 00293 37291

Drop:  54.4m (Trimble and LIDAR data)


The Trimble GeoXH 6000 gathering data at the southerly summit (SO 002 372) which in conjunction with LIDAR data de-twinned the two 391m map heighted summits of Cefn Bach

For details on the survey that in conjunction with LIDAR data de-twinned and confirmed the summit position of this hill please click {here}

Myrddyn Phillips and Aled Williams (August 2015)




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