Sunday, 13 August 2017

Mapping Mountains – Summit Relocations – Y Pellennig –The Remotest Hills of Wales


Y Pellennig –The Remotest Hills of Wales – Summit Relocations

Y Pellennig –The Remotest Hills of Wales comprise all Welsh hills whose summit is 2.5km or more from the nearest paved public road and which have a minimum 15m of drop, with the Change Register to this list available via Mapping Mountains.

The list is co-authored by Myrddyn Phillips and Aled Williams and the posts that have appeared on Mapping Mountains detailing the summit relocations to this list appear below presented chronologically in receding order.









Mapping Mountains - Summit Relocations - Y Pellennig - The Remotest Hills of Wales

Esgair Cerrig (SN 952 432) - 2nd summit relocation

Survey post for Esgair Cerrig

Significant Name Changes post for Esgair Cerrig


There has been a Summit Relocation initiated by LIDAR data analysed by Aled Williams and confirmed by a survey with the Trimble GeoXH 6000, to the listings of Y Pellennig and Y Pedwarau, with the survey that resulted in this summit relocation taking place on the 28th December 2016 in good, clear and bright conditions.


The two lists that this summit relocation affects are:


Y Pellennig - The Remotest Hills of Wales, with the criteria being all hills in Wales whose summit is 2.5km or more from the nearest paved public road that have a minimum 15m of drop.  This list is co-authored by Myrddyn Phillips and Aled Williams.

Y Pedwarau, with the criteria being all hills in Wales at and above 400m and below 500m in height that have a minimum 30m of drop.  This list is co-authored by Myrddyn Phillips and Aled Williams.

The name of the hill is Esgair Cerrig and this was derived from local enquiry (see Significant Name Changes) and access to it is restricted due to it being positioned within the confines of the Sennybridge Artillery Range Training Area.  The hill is situated in the Mynydd Epynt range, which is placed in the south-eastern part of Mid and West Wales (Region B, Sub-Region B2), and the hill is positioned above the small community of Llangamarch (Llangammarch Wells) to its north north-west and the small town of Llanwrtyd (Llanwrtyd Wells) to its west north-west. 

This hill’s summit position was previously given as SN 956 435 and this is where the current 456m spot height appears on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps.  However, prior to the survey with the Trimble GeoXH 6000 this hill’s summit was analysed using LIDAR data by Aled Williams.  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:


Esgair Cerrig

Summit Height:  456.3m

Summit Grid Reference:  SN 95226 43298


The analysis of LIDAR data pinpointed this hill’s position and its height was confirmed with the Trimble survey:


Esgair Cerrig

Summit Height:  456.4m (converted to OSGM15)

Summit Grid Reference:  SN 95224 43297 
    

Therefore the position of the relocated summit is at SN 95224 43297 and is featureless ground consisting of grass interspersed with reed grass beside a bomb crater, this position is within the uppermost 450m ring contour on Ordnance Survey maps although no spot height is given to it, the relocated summit is approximately 490 metres south-westward from where the previously listed summit is positioned.


The full details for the hill are:

Cardinal Hill:  Clepyn Melyn

Summit Height:  456.4m (converted to OSGM15)

Name:  Esgair Cerrig

OS 1:50,000 map:  147, 160

Summit Grid Reference (New Position):  SN 95224 43297 
     
Drop:  35.6m (converted to OSGM15)


The Trimble GeoXH 6000 gathering data at the summit of Esgair Cerrig, with the old position of the summit in the centre background of this photograph



Myrddyn Phillips and Aled Williams (January 2017)







Mapping Mountains - Summit Relocations - Y Pellennig - The Remotest Hills of Wales

Bryn Llwyd (SN 835 920) - 1st summit relocation

First survey post for Bryn Llwyd

Second survey post for Bryn Llwyd

Hill Reclassifications post for Bryn Llwyd

Significant Name Changes post for Bryn Llwyd 


There has been a Summit Relocation initiated by a survey with the Trimble GeoXH 6000 to the listings of Y PellennigYr Uchafion and 500m Twmpau, with the survey that resulted in this summit relocation being conducted on the 5th and 13th May 2016.

The three lists that this summit relocation affects are:


Y Pellennig - The Remotest Hills of Wales, with the criteria being all hills in Wales whose summit is 2.5km or more from the nearest paved public road that have a minimum 15m of drop.  This list is co-authored by Myrddyn Phillips and Aled Williams.

Yr Uchafion, this is the working title for a list that takes in all hills in Wales at and above 500m in height that have a minimum 15m of drop.  This list is co-authored by Myrddyn Phillips and Aled Williams.

500m Twmpau (thirty welsh metre prominences and upward), with the criteria being all Welsh hills at or above 500m and below 600m in height that have a minimum 30m of drop.  This list is authored by Myrddyn Phillips.


As the hill only entered the ranks of Pellennig hills due to this survey this listing of hills is being included within this Summit Relocations heading. 

The survey was conducted in the Pumlumon range of hills over two beautiful sunny days, with the hill situated mid-way between the towns of Machynlleth to its north-west and Llanidloes to its south-east.  

The name of the hill where the summit has been re-located to is Bryn Llwyd (SN 835 920) and the name of the hill where the summit has been re-located from is Bryn yr Ŵyn (SN 839 925).  Both summits and respective bylchau were surveyed with the Trimble with their summits being connected by a bwlch that is only 9.9m below the summit height of Bryn yr Ŵyn and 11.4m below the summit height of Bryn Llwyd.

The summits of both hills possess a small uppermost 500m ring contour on Ordnance Survey maps with no adjoined spot height, with the uppermost ring contour for Bryn Llwyd being the larger.

The critical bwlch for the higher of these hills in positioned to the south-west and to my knowledge their drop has only been surveyed on three occasions, once using a basic levelling survey (BLS) method, and the other two using the Trimble GeoXH 6000.  The results from each survey appear below:


Bryn Llwyd:  summit to critical bwlch, 102.5ft (31.2m) drop (BLS), 30.3m drop (Trimble).

Bryn yr Ŵyn:  summit to connecting bwlch with Bryn Llwyd, 42.5ft (13.0m) drop (BLS), 9.9m drop (Trimble).   


I conducted the basic levelling survey in July 2000 and sent the details to Michael Dewey.  Michael assessed the information and decided to include Bryn yr Ŵyn in his list to The 500-Metre Tops of England and Wales.  The margin of uncertainly associated with the BLS method is within the error tolerance of the result, and I have wanted to re-visit and survey both hills and produce accurate absolute heights for each, ever since.  Their heights as surveyed by the Trimble GeoXH 6000 appear below:


Bryn Llwyd 501.4m (converted to OSGM15) summit at SN 83574 92022 (average of four surveys conducted over two days)

Bryn yr Ŵyn 499.9m (converted to OSGM15) summit at SN 83919 92571 (average of five surveys conducted over two days)


Therefore the position of the relocated summit is at SN 83574 92022 and it consists of grass atop an ancient mound.  The summit area and the hill itself has relatively easy underfoot conditions and consists of moor grass with a path leading from the critical bwlch to the south-west toward the connecting bwlch with Bryn yr Ŵyn.  

This re-located summit position is not given a spot height on current Ordnance Survey maps and it is approximately 660 metres south south-westward from the previously listed summit position.


The full details for the hill are:


Cardinal Hill:  Pumlumon Fawr

Summit Height:  501.4m (converted to OSGM15, and average of four summit surveys)

Name:  Bryn Llwyd

OS 1:50,000 map:  135, 136

Summit Grid Reference (New Position):  SN 83574 92022 
  
Drop:  30.3m (converted to OSGM15)


The Trimble GeoXH 6000 gathering data at the summit of Bryn Llwyd, with the summit of Bryn yr Ŵyn on the right and in the background of this photograph

For details on the 1st Trimble survey and the 2nd Trimble survey that relocated the summit of this hill.

Myrddyn Phillips and Aled Williams (May 2016)








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