Wednesday, 23 September 2015

Mapping Mountains – Summit Relocations – Y Pedwarau and 300m Twmpau


Cefn Bach (SO 002 372)  


Please note; since this Summit Relocation was announced the two Cefn Bach hills have been analysed with LIDAR data resulting in the southerly hill being confirmed as the higher, this makes most of the detail given below as redundant, however it is being kept as an historical record. 


This is the seventeenth post under the heading of Summit Relocations, and the following details are retrospective as the Trimble survey that resulted in this summit relocation was conducted on 18th August 2015.

The seventeenth major summit relocation initiated from a 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.

The name of the hill is Cefn Bach and it is listed as a 390m Sub-Pedwar and as a 300m Tumpau.  The hill has twin map heighted 391m summits which are orientated north to south of one another.  It is the southerly summit at SO 002 372 that is currently listed as the 390m Sub-Pedwar with 55m of drop, whilst the northerly summit at SO 003 387 is currently listed as the 390m Double Sub-Pedwar with c 22m of drop.  These details are also applicable to the 300m Twmpau list with these summits listed as a Twmpau and Sub-Twmpau respectively.

The summits can be easily visited from a narrow lane to their south where one car can just 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.  The results and other map details and their clarification in regard to classification appear below.  These are detailed from north to south:


Cefn Bach:  391m map spot height at SO 003 387, new position for the 390m Sub-Pedwar and 300m Twmpau.  This gives a drop value of 56m.

Pt. 389.4m, Cefn Bach:  c 369m bwlch at SO 000 383.

Pt. 389.4m, Cefn Bach:  389.4m (converted to OSGM15) summit at SO 00293 37291, new position for the Double Sub-Pedwar and 300m Sub-Twmpau.  This gives a drop value of c 20m.  

Cefn Bach:  334.9m bwlch at SO 00287 36949.


This means that the hill classification is swapped between these two summits.  Therefore the position of the relocated summit for the 390m Sub-Pedwar and 300m Twmpau is at SO 003 387, and the position of the relocated summit for the 390m Double Sub-Pedwar and 300m Sub-Twmpau is at SO 00293 37291.


The full details for the 390m Sub-Pedwar and 300m Twmpau are:

Cardinal Hill:  Clepyn Melyn

Summit Height:  391m

Name:  Cefn Bach

OS 1:50,000 map:  160

Summit Grid Reference (New Position):  SO 003 387 
 
Drop:  56m



The full details for the 300m Sub-Twmpau are:

Cardinal Hill:  Clepyn Melyn

Summit Height:  389.4m (converted to OSGM15)

Name:  Pt. 389m, Cefn Bach

OS 1:50,000 map:  160

Summit Grid Reference (New Position):  SO 00293 37291 
 
Drop:  c 20m


The Trimble GeoXH 6000 gathering data at the new summit position of Pt. 389m, Cefn Bach which was the 390m Double Sub-Pedwar and is the 300m Sub-Twmpau, with the new position for the summit of the 390m Sub-Pedwar and 300m Twmpau in the centre background of this photograph

For details on the survey that relocated the summit of this hill please click {here}

Myrddyn Phillips and Aled Williams (August 2015)




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