Thursday 22 August 2019

Mapping Mountains – Summit Relocations – Yr Uchafion and 600m Twmpau


Cefn yr Ystrad (SO 086 137)

There has been a Summit Relocation to a hill that is listed in the Yr Uchafion and the 600m Twmpau with the summit height and its location being confirmed by a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips and Aled Williams on the 19th April 2019.

The criteria for the two listings that this summit relocation applies to are:

Yr Uchafion – Welsh hills at or above 500m in height that have 15m minimum drop.  The list is co-authored by Myrddyn Phillips and Aled Williams, with the Introduction to this list appearing on Mapping Mountains on the 4th November 2015.

600m Twmpau – Welsh hills at or above 600m and below 700m in height that have 30m minimum drop, with an accompanying sub category entitled the 600m Sub-Twmpau consisting of all Welsh hills at or above 600m and below 700m in height that have 20m or more and below 30m of drop.  With the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.  The list is authored by Myrddyn Phillips.

The name of the hill is Cefn yr Ystrad and it is adjoined to the Cymoedd Gwent group of hills, which are situated in the eastern part of South Wales (Region C, Sub-Region C2), and it is positioned with the A465 road to its south, with the Pontsticill Reservoir to its west and the Talybont Reservoir towards its north, and has the towns of Aberhonddu (Brecon) towards its north and Merthyr Tudful towards its south.

Extract from the Ordnance Survey 1:25,000 Explorer map

When this hill was first included in the listings that would later become known as the Yr Uchafion and 600m Twmpau the summit position was given to where the 617m map heighted triangulation pillar is situated.  The summit position for this hill was later changed to ground beside the ancient cairn which is named Carn y Bugail.  This summit relocation was based on Abney level surveys that indicated ground at the base of the ancient cairn was 0.8m higher than the flush bracket adjoined to the triangulation pillar.


Thee points were surveyed with the Trimble GeoXH 6000 and these results are given below:

Upright rock beside ancient cairn:  616.888m at SO 08810 13628

Grass at base of ancient cairn:  616.311m at SO 08793 13627

Small embedded rock beside trig pillar:  617.442 at SO 08696 13729


Gathering data on the upright rock beside the ancient cairn of Carn y Bugail

The 617.4m summit height produced by the Trimble GeoXH 6000 survey and its position in relation to the previously listed summit position on ground at the base of the ancient cairn comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

Gathering data at the base of the ancient cairn 

The term Summit Relocations applies to any listed hill whose summit meets the following criteria; where there are a number of potential summit positions within close proximity and the highest point is not where previously given, or a relocation of approximately 100 metres or more in distance from either the position of a map spot height or from where the summit of the hill was previously thought to exist, or when the summit of the hill is in a different field compared to where previously given, or when the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary that is judged to be a relatively recent man-made construct. 

Gathering data at the highest embedded rock beside the triangulation pillar

The summit height produced by the Trimble GeoXH 6000 survey is 617.4m and is positioned at SO 08696 13729, this position is approximately 140 metres north-west from where the old listed summit is positioned.


ills of Wales, and are reproduced below@
The full details for the hill are:

Group:  Cymoedd Gwent

Name:  Cefn yr Ystrad

OS 1:50,000 map:  160

Summit Height:  617.4m (converted to OSGM15)

Summit Grid Reference (new position):  SO 08696 13729
  
Bwlch Height:  439.9m (converted to OSGM15)

Bwlch Grid Reference:  SO 05261 17241

Drop:  177.5m (converted to OSGM15)



Myrddyn Phillips and Aled Williams (August 2019)






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