Wednesday, 23 August 2017

Mapping Mountains – Hill Reclassifications – Y Trechol – The Dominant Hills of Wales



Coed y Gaer (SO 004 843) – Lesser Dominant addition

There has been an addition to the listing of Y Trechol – The Dominant Hills of Wales confirmed by a survey with the Trimble GeoXH 6000; resulting in this hill being included in the Lesser Dominant sub list.

With the criteria for inclusion to the Dominant list being those Welsh P30 hills whose prominence equal or exceed half that of their absolute height, whilst the criteria for the Lesser Dominant list are those additional Welsh P30s whose prominence is 33% or more and below 50% of their absolute height.

The details relating to this hill’s inclusion as a Lesser Dominant hill are retrospective as the confirmation of its addition is dependent upon a survey with the Trimble GeoXH 6000 which was conducted on the 9th February 2014, with the relevant post giving the survey details appearing on Mapping Mountains on the 11th February 2014.

When the sub category of hills accompanying the Welsh P30 lists published on Geoff Crowder’s v-g.me website were standardised with interpolated drop values, this hill was listed with an estimated c 119m of drop based on its 362m summit spot height and an estimated bwlch height of c 243m, these values gave this hill 32.87% Dominance, which was insufficient for it to be classified as a Lesser Dominant.  The drop value was subsequently altered due to a 241m bwlch spot height appearing on the Ordnance Survey enlarged mapping hosted on the Geograph website, this resulted in the hill’s Dominance also being amended.

The name of the hill is Coed y Gaer and it is listed in the Pegwn Mawr group and is placed in the Region of Mid and West Wales (Region B, Sub-Region B1) with its Cardinal Hill being Pegwn Mawr (SO 023 812), and is situated above the A 470 road and the Afon Hafren (River Severn) which are to its north, and it is positioned between the small community of Llandinam to the north north-east and the town of Llanidloes to the west.

As the hill is not a part of designated open access land permission to visit should be sought, for those wishing to do so a minor lane to the south of the hill gives access to steep slopes leading to the summit.

The qualification of Coed y Gaer to Lesser Dominant status has been confirmed by the survey with the Trimble GeoXH 6000 resulting in a summit height of 359.9m (converted to OSGM15) and a bwlch height of 238.3m (converted to OSGM15) which gives the hill 121.7m of drop and 33.80% Dominance.

  

The full details for the hill are:

Group:  Pegwn Mawr

Name:  Coed y Gaer

Dominance:  33.80%

OS 1:50,000 map:  136

Summit Grid Reference:  SO 00488 84392

Summit Height:  359.9m (converted to OSGM15)

Drop Summit to Bwlch:  121.7m (converted to OSGM15)

Drop Bwlch to ODN:  238.3m


Gathering data at the summit of Coed y Gaer


Myrddyn Phillips (August 2017)

Tuesday, 22 August 2017

Mapping Mountains – Hill Reclassifications – Humps


Llechwedd Melyn (SN 616 987) – Subhump reclassified to Hump

This is the third in a series of Hill Reclassification posts that detail hills whose status has been altered in the listing of the Humps (HUndred Metre Prominences) through map study and / or surveys that I have instigated.

The hill name used in this and forthcoming posts is that used in the listing of Humps, therefore individual names may not match those that are used in listings I am directly associated with.  However, I am of firm belief that listed hill names used by other authors should be respected when giving detail within other people’s lists, however inappropriate some hill names may be considered.

This and forthcoming posts are retrospective as many of these hill reclassifications were initiated from studying the Ordnance Survey enlarged mapping that is hosted on the Geograph website, and for the reclassifications that affected the Humps the third email I posted on the RHB Yahoo Group forum was dated 09.04.12.

The listing of Humps was published in book format by Lulu in 2009 and entitled More Relative Hills of Britain, its author; Mark Jackson gives credit to a number of people who contributed toward the formation of this list, these include; Eric Yeaman, Alan Dawson, Clem Clements, Rob Woodall, Bernie Hughes, Pete Ridges and others.  When the list was published in book format there were 2987 Humps listed with their criteria being any British hill that has 100m or more of drop, accompanying the main list is a sub category entitled the Subhumps, with the criteria being any British hill that has 90m or more and below 100m of drop.


More Relative Hills of Britain by Mark Jackson


The details for the reclassification appear below:

There has been a reclassification to the listing of the Humps (HUndred Metre Prominences) due to consulting the Ordnance Survey enlarged mapping that is hosted on the Geograph website, with these details being posted on the RHB Yahoo Group forum on 09.04.12.

Prior to this notification Mark Jackson had listed this hill as a Subhump with c 98m of drop, however with a 196m summit spot height on the Ordnance Survey 1:25,000 Explorer map and a 96m spot height appearing on the area of this hill’s bwlch on the Ordnance Survey enlarged mapping hosted on the Geograph website, these values give this hill 100m of drop, which is sufficient for it to be reclassified to Hump status.

Extract from the Ordnance Survey enlarged mapping hosted on the Geograph website showing the 96m spot height on the area of this hill's bwlch and its 196m summit spot height

The hill appears under the name of Llechwedd Melyn in the Humps, with this name having appeared in the original 100m Welsh P30 list published on Geoff Crowder’s v-g.me website and which was derived from Ordnance Survey maps.  As this hill comprises bounded land its details were examined on the Tithe map to the parish of Tywyn, and the enclosed land at the summit of the hill is named Ffridd y Garw on this map, with the enclosed land to the east of the summit named Llechwedd and the enclosed land to the south-east named Gribin.  The latter name matches that used on the Ordnance Survey enlarged mapping on the Geograph website, whilst the name Llechwedd is complimentary to the name Llechwedd Melyn and is applicable to the eastern lower slopes of this hill, whilst the enclosed land taking in the summit of this hill is named Ffridd y Garw.

The hill is adjoined to the Tarennydd range of hills and is situated overlooking the Happy Valley which is to its north-east and the A493 road and the coast which is to its west, with the town of Tywyn positioned to the north-west of the hill.

The addition of this hill to Hump status was accepted by Mark Jackson and its new classification augmented in to the listing of the Humps on the 18.04.12.


The full details for the hill are:


Name:  Llechwedd Melyn (as listed in the Humps)

Summit Height:  196m

OS 1:50,000 map:  135

OS 1:25,000 map:  23

Summit Grid Reference:  SN 61632 98767

Drop:  100m



Myrddyn Phillips (August 2017)



Monday, 21 August 2017

Mapping Mountains – Summit Relocations – 500m Twmpau


500m Twmpau – Summit Relocations

The 500m Twmpau (thirty welsh metre prominences and upward) are the Welsh hills at or above 500m and below 600m in height that have a minimum drop of 30m.  Accompanying the main P30 list is a sub list entitled the 500m Sub-Twmpau with the qualification to this sub category being all Welsh hills at or above 500m and below 600m in height with 20m or more and below 30m of drop.

The list is authored by Myrddyn Phillips and the posts that have appeared on Mapping Mountains detailing the summit relocations to the main P30 list and the sub list appear below presented chronologically in receding order.







Mapping Mountains - Summit Relocations - 500m Twmpau

Mynydd Ton (SS 949 940) - 2nd summit relocation

Survey post for Mynydd Ton

Significant Height Revisions post for Mynydd Ton


There has been a Summit Relocation initiated by a survey with the Trimble GeoXH 6000  to the listings of Yr Uchafion and the 500m Twmpau, with the survey that resulted in this summit relocation being conducted on the 23rd July 2016 in good, clear and sheltered conditions.


The two lists that this summit relocation affects are:

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.


The survey was conducted in the range of hills known as the Y Cymoedd, these are the hills associated with the south Wales valleys.  The hill is situated between Cwm Ogwr Fawr to its west and the Rhondda Fawr valley to its east and is positioned above the towns of Treorci (Treorchy) and Treherbert to its north and Nant-y-moel, Price Town and Ogmore Vale to its south-west.

Access to the hill is relatively easy as a track leaves the A 4061 near to its high point and continues south-eastward to the north-western edge of a large conifer plantation, a path continues south-eastward adjacent to the forest boundary gaining the access point to a wide forest break which is relatively near the summit of this hill.

The name of the hill is Mynydd Ton and prior to the survey with the Trimble GeoXH 6000 the height of the hill was listed as 539m at SS 94796 93958 which is beside an ancient cairn.  This height was based on a 1,769.3ft surface height given on the Ordnance Survey Six-Inch map published in 1885.  The 539m figure was a relatively new addition to this hill’s listed height as its summit position was originally listed as ground beside its map heighted 535m triangulation pillar situated at SS 94931 94058.

The highest ground at the base of and beside the ancient cairn was surveyed with the Trimble GeoXH 6000 as being 534.2m (converted to OSGM15) high.  The processed data gave Estimated Accuracies of 5-15cm: 99.41%, with the Standard Deviation being 0.0m, and the margin of uncertainty given for the height placement of the Trimble was 0.1m.  All of the above signify that the data set was good and accurate to within the parameters of the equipment.

I had previously visited this hill in February 2003 and judged ground approximately one minute walk away from the trig pillar to be slightly higher than ground at the base of the trig pillar, and as the flush bracket adjoined to the trig pillar is given a height of 535.335m in the OS Trig Database it means that ground at its base is approximately 535m high.  This figure is dependent upon the accuracy of the flush bracket height which is given as 3rd order.   Therefore the ground at the base of or near to the triangulation pillar is likely to be higher than that beside the ancient cairn.

Therefore the position of the relocated summit is at SS 94931 94058 and consists of ground at the base of, or near to the triangulation pillar.  This re-located summit position is at the hill’s originally listed summit and is given a 535m height on current Ordnance Survey maps and it is approximately 175 metres north-eastward from the previously listed summit position.


The full details for the hill are:

Cardinal Hill:  Werfa

Summit Height:  535m

Name:  Mynydd Ton

OS 1:50,000 map:  170

Summit Grid Reference (New Position):  SS 94931 94058 
      
Drop:  92m



The Trimble GeoXH 6000 gathering data beside the ancient cairn on Mynydd Ton, with the relocated position of the summit approximately 175 metres to the north-east and to the right of the forest break in the centre background of this photograph



Myrddyn Phillips and Aled Williams (August 2016)







Mapping Mountains - Summit Relocations - 500m Twmpau

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

First survey post for Bryn Llwyd

Second survey 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 (May 2016)








Saturday, 19 August 2017

Mapping Mountains – Hill Reclassifications – 200m Twmpau


Erw Penlan (SO 045 495) – 200m Sub-Twmpau addition

There has been a confirmation of an addition to the 200m Twmpau (thirty welsh metre prominences and upward) ranks of hills due to a survey with the Trimble GeoXH 6000, with the survey that confirmed this addition being conducted on the 13th June 2017.

The criteria for 200m Twmpau status is all Welsh hills at or above 200m and below 300m in height with 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 200m and below 300m in height with 20m or more and below 30m of drop, and it is the inclusion of this hill in the 200m Sub-Twmpau that has been confirmed. 

The hill did not appear in the original Welsh P30 lists on Geoff Crowder’s v-g.me website as it did not meet the criteria then adopted for the Hills to be surveyed sub list.  The hill was later classified and listed in the sub category after this was standardised and interpolated drop values added, and was included when the updates to the 200m Welsh P30s were published for the Mynydd Epynt group of hills on Mapping Mountains on the 25th August 2014.  The listing this hill is now a part of is named Twmpau (thirty welsh metre prominences and upward) and its height, drop and status was confirmed by a survey with the Trimble GeoXH 6000.   

Prior to the survey with the Trimble GeoXH 6000 the hill was listed by the name of Coetgae Fawr with an estimated c 21m of drop, based on the 213m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated bwlch height of c 192m based on interpolation of bwlch contouring between 190m – 200m.

The name that this hill is being listed by is Erw Penlan (see Significant Name Changes) and it is adjoined to the Mynydd Epynt range, which is situated in the south-eastern part of Mid and West Wales (Region B, Sub-Region B2) with its Cardinal Hill being Clepyn Melyn (SN 961 464), and it is positioned above the A 483 road which is to the hill’s north and east, with the town of Llanfair-ym-Muallt (Builth Wells) positioned to its north.

As the hill does not form a part of designated open access land permission to visit should be sought, for those wishing to do so a public footpath connects between minor country lanes to the north and south of the hill’s summit and proceeds around the upper western part of the hill.


The full details for the hill are:


Cardinal Hill:  Clepyn Melyn

Summit Height:  212.1m (converted to OSGM15)

Name:  Erw Penlan

OS 1:50,000 map:  147

Summit Grid Reference:  SO 04597 49535  

Drop:  20.9m (converted to OSGM15)


Erw Penlan (SO 045 495) now confirmed as a 200m Sub-Twmpau addition




Myrddyn Phillips (August 2017)







Friday, 18 August 2017

Mapping Mountains – Hill Reclassifications – Humps


Vivod Mountain (SJ 169 400) – Subhump addition

This is the second in a series of Hill Reclassification posts that give details to hills whose status has been altered in the listing of the Humps (HUndred Metre Prominences) through map study and / or surveys that I have conducted.

The hill name used in this and forthcoming posts is that used in the listing of Humps, therefore individual names may not match those that are used in listings I am directly associated with.  However, I am of firm belief that listed hill names used by other authors should be respected when giving detail within other people’s lists, however inappropriate some hill names may be considered.

This and forthcoming posts are retrospective as many of these hill reclassifications were initiated from studying the Ordnance Survey enlarged mapping that is hosted on the Geograph website, and for the reclassifications that affected the Humps the second email I posted on the RHB Yahoo Group forum was dated 30.01.12.

The listing of Humps was published in book format by Lulu in 2009 and entitled More Relative Hills of Britain, its author; Mark Jackson gives credit to a number of people who contributed toward the formation of this list, these include; Eric Yeaman, Alan Dawson, Clem Clements, Rob Woodall, Bernie Hughes, Pete Ridges and others.  When the list was published in book format there were 2987 Humps listed with their criteria being any British hill that has 100m or more of drop, accompanying the main list is a sub category entitled the Subhumps, with the criteria being any British hill that has 90m or more and below 100m of drop.


More Relative Hills of Britain by Mark Jackson


The details for the reclassification appear below:

There has been an addition to the listing of the Humps (HUndred Metre Prominences) due to consulting the Ordnance Survey 1:25,000 Explorer map and later followed by the enlarged mapping that is hosted on the Geograph website, with these details being posted on the RHB Yahoo Group forum on 30.01.12.

Prior to this notification Mark Jackson had listed this hill with 85m of drop, this drop value was based on a 559m summit height given in his Tumps list and a bwlch height of 474m, with the latter based on a spot height positioned at SJ 150 393.  This bwlch position was incorrect as it is approximately 1.1km west from where the critical bwlch of this hill is positioned and which already had bwlch contouring between 460m – 470m, which is lower than the 474m spot height that had been used for the height of this hill’s bwlch in the Tumps.

Extract from the Ordnance Survey 1:25,000 Explorer map showing the position of the 474m spot height and lower contouring at the position of the critical bwlch approximately 1km east of its position

The hill appears under the name of Vivod Mountain in the Humps, with this name appearing on current Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps.  The word Vivod is an anglicised corruption of the radical unmutated word Meifod, this being a Welsh word meaning middle dwelling.  The landowning estate of Vivod / Y Feifod can be found north-eastward from this hill’s summit.  Although locally known in some areas as Vivod (Feifod) Mountain, the locally known name in the Welsh speaking community is Mynydd y Feifod. 

The addition of this hill to Subhump status was accepted by Mark Jackson and its new classification augmented in to the listing of the Humps on the 30.01.12.


The full details for the hill are:


Name:  Vivod Mountain (as listed in the Humps)

Summit Height:  559m (as listed in the Humps)

OS 1:50,000 map:  125

OS 1:25,000 map:  255

Summit Grid Reference:  SJ 16965 40002

Drop:  96m (as listed in the Humps)



Myrddyn Phillips (August 2017)

Thursday, 17 August 2017

Mapping Mountains – Summit Relocations – The Welsh 500m P15s (Yr Uchafion)


The Welsh 500m P15s (Yr Uchafion) – Summit Relocations

The Welsh 500m P15s are the Welsh hills at or above 500m in height that have a minimum drop of 15m.  Accompanying the main P15 list are three sub lists; these are the 500m Subs, 490m Subs and the Double Subs with their criteria detailed in the respective Change Registers which are linked in their above titles, with details to this list given in the Introduction that was published on Mapping Mountains in November 2015.

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 the main P15 list and the sub lists appear below presented chronologically in receding order.








Mapping Mountains - Summit Relocations - The Welsh 500m P15s (Yr Uchafion)

Mynydd Ton (SS 949 940) - 2nd summit relocation

Survey post for Mynydd Ton

Significant Height Revisions post for Mynydd Ton


There has been a Summit Relocation initiated by a survey with the Trimble GeoXH 6000  to the listings of Yr Uchafion and the 500m Twmpau, with the survey that resulted in this summit relocation being conducted on the 23rd July 2016 in good, clear and sheltered conditions.

The two lists that this summit relocation affects are:

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.

The survey was conducted in the range of hills known as the Y Cymoedd, these are the hills associated with the south Wales valleys.  The hill is situated between Cwm Ogwr Fawr to its west and the Rhondda Fawr valley to its east and is positioned above the towns of Treorci (Treorchy) and Treherbert to its north and Nant-y-moel, Price Town and Ogmore Vale to its south-west.

Access to the hill is relatively easy as a track leaves the A 4061 near to its high point and continues south-eastward to the north-western edge of a large conifer plantation, a path continues south-eastward adjacent to the forest boundary gaining the access point to a wide forest break which is relatively near the summit of this hill.

The name of the hill is Mynydd Ton and prior to the survey with the Trimble GeoXH 6000 the height of the hill was listed as 539m at SS 94796 93958 which is beside an ancient cairn.  This height was based on a 1,769.3ft surface height given on the Ordnance Survey Six-Inch map published in 1885.  The 539m figure was a relatively new addition to this hill’s listed height as its summit position was originally listed as ground beside its map heighted 535m triangulation pillar situated at SS 94931 94058.

The highest ground at the base of and beside the ancient cairn was surveyed with the Trimble GeoXH 6000 as being 534.2m (converted to OSGM15) high.  The processed data gave Estimated Accuracies of 5-15cm: 99.41%, with the Standard Deviation being 0.0m, and the margin of uncertainty given for the height placement of the Trimble was 0.1m.  All of the above signify that the data set was good and accurate to within the parameters of the equipment.

I had previously visited this hill in February 2003 and judged ground approximately one minute walk away from the trig pillar to be slightly higher than ground at the base of the trig pillar, and as the flush bracket adjoined to the trig pillar is given a height of 535.335m in the OS Trig Database it means that ground at its base is approximately 535m high.  This figure is dependent upon the accuracy of the flush bracket height which is given as 3rd order.   Therefore the ground at the base of or near to the triangulation pillar is likely to be higher than that beside the ancient cairn.

Therefore the position of the relocated summit is at SS 94931 94058 and consists of ground at the base of, or near to the triangulation pillar.  This re-located summit position is at the hill’s originally listed summit and is given a 535m height on current Ordnance Survey maps and it is approximately 175 metres north-eastward from the previously listed summit position.


The full details for the hill are:

Cardinal Hill:  Werfa

Summit Height:  535m

Name:  Mynydd Ton

OS 1:50,000 map:  170

Summit Grid Reference (New Position):  SS 94931 94058 
      
Drop:  92m



The Trimble GeoXH 6000 gathering data beside the ancient cairn on Mynydd Ton, with the relocated position of the summit approximately 175 metres to the north-east and to the right of the forest break in the centre background of this photograph



Myrddyn Phillips and Aled Williams (August 2016)







Mapping Mountains - Summit Relocations - The Welsh 500m P15s (Yr Uchafion)

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

First survey post for Bryn Llwyd

Second survey 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 Pellennig, Yr 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)