Sunday, 18 June 2017

Mapping Mountains – Hill Reclassifications – 500m Twmpau



500m Twmpau – Hill Reclassifications

The 500m Twmpau (thirty welsh metre prominences and upward) are the Welsh hills at or above 500m and below 60om 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 Introduction to this list is linked in the above title.

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







Mapping Mountains - Hill Reclassifications - 500m Twmpau

Garn Fach (SO 041 815) – 500m Sub-Twmpau addition (6th reclassification)


There has been an addition to the listing of Twmpau (thirty welsh metre prominences and upward) hills due to analysis of LIDAR data by Aled Williams.  The Twmpau is the title for the list of Welsh P30s and takes in all Welsh hills that have a minimum 30m of drop, with this addition affecting the 500m height band of hills within the Twmpau.

Accompanying the main list of Twmpau hills is a sub category, with the criteria for this sub list in the 500m height band being all Welsh hills at or above 500m and below 600m in height with 20m or more and below 30m of drop.  It is this sub category that this addition affects and details to this height band of the Twmpau were published on the Mapping Mountains site on 15th June 2015.

Prior to analysis of LIDAR data the hill had been listed with 19m of drop based on the 503m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and the 484m bwlch spot height that appears on the Ordnance Survey 1:25,000 Explorer map.

The name of the hill is Garn Fach and it is situated in the Pegwn Mawr group of hills with its Cardinal Hill being Pegwn Mawr (SO 023 812) and is placed in the Region of Mid and West Wales (Region B, Sub-Region B1).  The hill is situated between the small community of Llanbadarn Fynydd towards its south-east and the town of Llanidloes towards its west north-west.

If wanting to visit the hill it is situated on open access land which is covered in a conifer plantation, however on my only visit I followed a forest track leading in from the east which gave access to a forest ride that led towards the summit.

The addition of Garn Fach to 500m Sub-Twmpau status is due to the analysis of 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:


Garn Fach

Summit Height:  504.3m

Summit Grid Reference:  SO 04184 81512

Bwlch Height:  484.3m

Bwlch Grid Reference:  SO 03783 81771

Drop:  20.0m


Therefore, the 504.3m LIDAR data produced for the summit position at SO 04184 81512 and the 484.3m LIDAR data produced for the bwlch position at SO 03783 81771 gives this hill 20.0m of drop which is sufficient for its inclusion as a 500m Sub-Twmpau.


The full details for the hill are:


Cardinal Hill:  Pegwn Mawr

Summit Height:  504.3m (LIDAR data)

Name:  Garn Fach

OS 1:50,000 map:  136

Summit Grid Reference:  SO 04184 81512

Drop:  20.0m (LIDAR data)


The overall total for the 500m Twmpau remains at 225 hills with the overall total for the 500m Sub-Twmpau increasing by one to 97 hills.  The list of the 500m Twmpau was published on 15th June 2015 with all subsequent changes having been detailed on Mapping Mountains. 


My thanks to Aled Williams for sending the details of this hill to me

Myrddyn Phillips (September 2017)






Mapping Mountains - Hill Reclassifications - 500m Twmpau

Craig Stwlan (SH 667 446) – 500m Sub-Twmpau deletion (5th reclassification)


There has been a deletion to the listing of Twmpau (thirty welsh metre prominences and upward) hills due to analysis of LIDAR data by Aled Williams.  The Twmpau is the title for the list of Welsh P30s and takes in all Welsh hills that have a minimum 30m of drop, with this deletion affecting the 500m height band of hills within the Twmpau.

Accompanying the main list of Twmpau hills is a sub category list of hills, with the criteria for this sub list in the 500m height band of hills being all Welsh hills at or above 500m and below 600m in height with 20m or more and below 30m of drop.  Details to this height band of the Twmpau were published on the Mapping Mountains site on 15th June 2015.

Prior to analysis of LIDAR data the hill had been listed with c 20m of drop based on the 568m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated bwlch height of c 548m based on interpolation of bwlch contouring between 540m – 550m.

The hill is situated in the Moelwynion group of hills with its Cardinal Hill being Moelwyn Mawr (SH 658 448) and is placed in the Region of North Wales (Region A, Sub-Region A1).  The hill is situated with the town of Blaenau Ffestiniog to the east north-east and the small village of Croesor to the west.

If wanting to visit the hill it can be easily accessed from the east north-east from the end of the paved public road which is situated above the small community of Tanygrisiau, beyond a locked gate the paved road continues up toward the reservoir of Llyn Stwlan, and Craig Stwlan is positioned just above the north-eastern part of this lake.

The name of the hill is Craig Stwlan and its deletion from 500m Sub-Twmpau status is due to the analysis of 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:


Craig Stwlan

Summit Height:  568.2m

Summit Grid Reference:  SH 66735 44655

Bwlch Height:  548.5m

Bwlch Grid Reference:  SH 66693 44715

Drop:  19.7m


Therefore, the 568.2m LIDAR data produced for the summit position at SH 66735 44655 and the 548.5m LIDAR data produced for the bwlch position at SH 66693 44715 gives this hill 19.7m of drop which is insufficient for it to retain its status as a 500m Sub-Twmpau.


The full details for the hill are:

Cardinal Hill:  Moelwyn Mawr

Summit Height:  568.2m (LIDAR data)

Name:  Craig Stwlan

OS 1:50,000 map:  124

Summit Grid Reference:  SH 66735 44655

Drop:  19.7m (LIDAR data)


The overall total for the 500m Twmpau remains at 225 hills with the overall total for the 500m Sub-Twmpau decreasing by one to 96 hills.  The list of the 500m Twmpau was published on 15th June 2015 with all subsequent changes having been detailed on Mapping Mountains


My thanks to Aled Williams for sending the details of this hill to me.

Myrddyn Phillips (May 2017)






Mapping Mountains - Hill Reclassifications - 500m Twmpau

Pt. 499.1m (SN 863 760) - 500m Sub-Twmpau reclassified to 400m Sub-Pedwar and 490m Sub-Uchaf (4th reclassification)


There has been a reclassification to the listing of Twmpau (thirty welsh metre prominences and upward) hills due to analysis of LIDAR data by Aled Williams.  The hill was previously listed in the 500m height band of Sub-Twmpau hills and it has now been reclassified to a 400m Sub-Pedwar and 490m Sub-Uchaf, with the criteria for the sub hills in the 500m Twmpau listing being 500m or more and below 600m in height with 20m or more and below 30m of drop.  Details to this height band of the Twmpau were published on the Mapping Mountains site on 15th June 2015.

The hill had been listed with 27.9m of drop and an estimated c 500m summit height based on the flat topped nature of its summit area in relation to the dimension of the small uppermost 500m ring contour that appears on current Ordnance Survey mapping.  

The hill is situated in the Elenydd group of hills with its Cardinal Hill being Draws Drum (SN 790 811) and is placed in the Region of Mid and West Wales (Region B, Sub-Region B2).  The hill is situated with the small community of Llangurig to the north-east and Cwmystwyth to the west south-west and is positioned directly above and to the north of the narrow mountain road that heads north-westward from Rhaeadr Gwy (Rhayader).

As the hill is immediately above a road access to it is relatively easy from where a public footpath is indicated on Ordnance Survey maps leaving the road to the west south-west of the summit and following a stream valley up toward the hill’s west, from here the ascent to the featureless flat topped summit area is on ground that is relatively easy compared to other hills in the vicinity.

The name of the hill is currently being listed by the point (Pt. 499.1m) notation and its reclassification from the ranks of 500m Sub-Twmpau is due to analysis of 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:


Pt. 499.1m

Summit Height:  499.1m

Summit Grid Reference:  SN 86343 76073

Bwlch Height:  471.0m

Bwlch Grid Reference:  SN 86323 76358

Drop:  28.1m


Therefore, the 499.1m LIDAR data produced for the summit position at SN 86343 76073 and the 471.0m LIDAR data produced for the bwlch position at SN 86323 76358 gives this hill 28.1m of drop, which is in good accordance with the value produced for this hill when surveyed by John Barnard, Graham Jackson, David Purchase and myself in June 2008 using a level and staff resulting in a drop of 27.9m.  Therefore with a summit height below 500m this hill is not high enough to retain its classification as a 500m Sub-Twmpau.  This now revises the total in the 500m Twmpau which will be updated accordingly.


The full details for the hill are:

Cardinal Hill:  Draws Drum

Summit Height:  499.1m (LIDAR data)

Name:  Pt. 499.1m

OS 1:50,000 map:  135, 136, 147

Summit Grid Reference:  SN 86343 76073
   
Drop:  27.9m (line survey)



My thanks to Aled Williams for sending the details of this hill to me.


Myrddyn Phillips (March 2017)






Mapping Mountains - Hill Reclassifications - 500m Twmpau

Mynydd Llangatwg (SO 202 145) - 500m Twmpau reclassified to 500m Sub-Twmpau (3rd reclassification)


There has been a reclassification to the listing of Twmpau (thirty welsh metre prominences and upward) hills due to analysis of LIDAR data by Aled Williams.  The hill was previously listed in the 500m height band of Twmpau hills and it has now been reclassified to a 500m Sub-Twmpau, with the criteria for the sub hills being 500m or more and below 600m in height with 20m or more and below 30m of drop.  Details to this height band of the Twmpau were published on the Mapping Mountains site on 15th June 2015.

The hill had been listed with c 31m of drop, based on the 529m summit spot height that appears on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps and an estimated bwlch height of c 498m based on bwlch contouring between 490m – 500m.  The summit area of the hill has two ancient cairns on it as well as a triangulation pillar with an adjoined flush bracket height of 529.044m.  

The hill is situated in the easterly part of the Bannau Brycheiniog (Brecon Beacons) group of hills with its Cardinal Hill being Pen y Fan (SO 012 215) and is placed in the Region of South Wales (C-2).  It is situated between the towns of Bryn-mawr to its south, Gilwern to its east and Crug Hywel (Crickhowell) to its north north-east.

The hill can be accessed from public footpaths originating from its north and from its south; however one of the easiest ways to its summit is from the east where a track heads toward the summit from a minor road that reaches over 350m high.

The name of the hill is Mynydd Llangatwg, however it is also recorded as Mynydd Pencyrn on Ordnance Survey maps and its reclassification to a Sub-Twmpau is due to the analysis of LIDAR data by Aled.  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:


Mynydd Llangatwg

Summit Height:  528.4m

Summit Grid Reference:  SO 20283 14511

Bwlch Height:  499.6m

Bwlch Grid Reference:  SO 18452 15398

Drop:  28.8m


Therefore, the 528.4m LIDAR data produced for the summit position at SO 20283 14511 and the 499.6m LIDAR data produced for the bwlch position at SO 18452 15398 is sufficient for this hill to be reclassified from a 500m Twmpau to a 500m Sub-Twmpau with 28.8m of drop.

This now revises the total in the 500m Twmpau which will be updated accordingly.


The full details for the hill are:

Cardinal Hill:  Pen y Fan

Summit Height:  528.4m (LIDAR data)

Name:  Mynydd Llangatwg

OS 1:50,000 map:  161

Summit Grid Reference:  SO 20283 14511 
  
Drop:  28.8m (LIDAR data)



My thanks to Aled Williams for sending the details of this hill to me.


Myrddyn Phillips (January 2017)






Mapping Mountains - Hill Reclassifications - 500m Twmpau

Cwar yr Ystrad (SO 083 142) - 500m Sub-Twmpau addition (2nd reclassification)


There has been a new addition to the listing of Twmpau (thirty welsh metre prominences and upward) hills due to analysis of LIDAR data by Aled Williams.  The hill is listed in the 500m height band of Sub-Twmpau, with the criteria for the sub hills being 500m or more and below 600m in height with 20m or more and below 30m of drop.  Details to this height band of the Twmpau were published on the Mapping Mountains site on 15th June 2015.

The hill did not appear in the Sub-List which accompanied the original Welsh P30 listings on Geoff Crowder’s v-g.me website as the Sub-List only included hills whose map details showed that when surveyed they may stand a chance of qualification to the main P30 list, with the title of the Sub-List being ‘Hills to be surveyed.’  And as this hill is a part of a quarry current 1:50,000 and 1:25,000 Ordnance Survey maps do not give it any ring contours, as is the norm for areas of land that have been quarried.  The hill is of interest as it is only now listed as a Sub-Twmpau through the quarrying activities of past years that has resulted in producing a new bwlch for the hill.   Since first publication this Sub-List has been standardised and now includes all hills that have a minimum of 20m of drop and below 30m of drop.

The hill is situated in the southern part of the Bannau Brycheiniog (Brecon Beacons) group of hills with its Cardinal Hill being Pen y Fan (SO 012 215) and is placed in the Region of South Wales (C-2).  As its name suggests the hill is a part of a quarry with its qualification as a Sub-Twmpau partly due to past quarry activities, it is situated between the Pentwyn and Pontsticill Reservoirs to its west and the Talybont Reservoir to its north north-east, with the town of Merthyr Tudful to its south south-west and the small community of Trefil to its east south-east.

The hill can be accessed from a number of directions on public footpaths including from its south-west and from its north, whilst the route from the paved road north of Trefil also gives access onto the quarry track, but if wishing to ascend from this direction it should be noted that there is a barrier across the road beyond Trefil that is locked at 5.00pm and unlocked at 6.30am with online write ups stating this barrier is locked at weekends.

The name of the hill is Cwar yr Ystrad and its inclusion as a Sub-Twmpau is due to the analysis of LIDAR data by Aled.  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:


Cwar yr Ystrad

Summit Height:  579.9m

Summit Grid Reference:  SO 08358 14245

Bwlch Height:  558.9m

Bwlch Grid Reference:  SO 08376 14189

Drop:  21.0m


Therefore, the 579.9m LIDAR data produced for the summit position at SO 08358 14245 and the 558.9m LIDAR data produced for the bwlch position at SO 08376 14189 is sufficient for this hill to be classified as a Sub-Twmpau with 21.0m of drop.

This now revises the total in the 500m Twmpau which will be updated accordingly.


The full details for the hill are:

Cardinal Hill:  Pen y Fan

Summit Height:  579.9m (LIDAR data)

Name:  Cwar yr Ystrad

OS 1:50,000 map:  160

Summit Grid Reference:  SO 08358 14245
  
Drop:  21.0m (LIDAR data)



A wintry scene with the new 500m Sub-Twmpau Cwar yr Ystrad in the background with its summit directly above the roof of Ed's car

My thanks to Aled Williams for sending the details of this hill to me.


Myrddyn Phillips (January 2017)







Mapping Mountains - Hill Reclassifications - 500m Twmpau

Twyn Walter (SN 828 175) - 500m Twmpau reclassified to 500m Sub-Twmpau (1st reclassification)

Survey post for Twyn Walter

Significant Height Revisions post for Twyn Walter


There has been a reclassification of a 500m Twmpau hill by surveying with the Trimble.   The hill is situated in the south-eastern lands of Y Mynydd Du in South Wales, and is positioned north-west of Glyntawe and the A4067 as it speeds its way between Pontsenni (Sennybridge) to the north and Ystradgynlais to the south.

These details are retrospective as the Trimble GeoXH 6000 survey that resulted in the reclassification of this hill from 500m Twmpau to 500m Sub-Twmpau was conducted on 10th July 2014, in the company of Mark Trengove when we visited the Remotest spot in mainland Wales, as well as the Remotest hill in mainland Wales.

Access to the hill from the south-east of its summit is relatively easy as a broad path ascends from near to the Campsite entrance that is adjacent to Dan yr Ogof Showcaves.  As height is gained this path resembles a vehicle track and eventually heads north-west into the remote grasslands of Mynydd Du, on its way it passes within approximately 260 metres of the summit.
     
The hill is named Twyn Walter (written as Twynwalter on current Ordnance Survey maps) and its summit is positioned at SN 828 175.  The hill was listed with c 31m of drop based on a 509m summit spot height and an estimated bwlch height of c 478m.  The area of the bwlch has a number of sink holes on it which complicates pinpointing where the critical bwlch is positioned.  However, contouring suggests that there are two distinct positional possibilities for where this critical bwlch lies, these are at SN 82525 17584 and SN 82611 17986.

The survey with the Trimble GeoXH 6000 resulted in a 502.1m (converted to OSGM15) summit height, unfortunately daylight was quickly disappearing and this was the last survey of a long day on the hill and this dictated that the two options for the position of the bwlch were not surveyed.  However, the dramatic decrease in summit height from the 509m map height to the 502.1m (converted to OSGM15) surveyed height and the re-evaluated and estimated bwlch height from contour interpolation of c 476m gives this hill a drop value of only c 26m.

This now brings the overall total for the 500m Twmpau hills to 226, please click {here} to access the list and {here} for its detailed Introduction.


The full details for the hill are:

Cardinal Hill:  Fan Brycheiniog

Summit Height:  502.1m (converted to OSGM15)

Name:  Twyn Walter

OS 1:50,000 map:  160

Summit Grid Reference:  SN 82837 17506

Drop:  c 26m


Gathering data at the summit of Twyn Walter, which resulted in this hill being reclassified from a 500m Twmpau to a 500m Sub-Twmpau

For details on the survey that reclassified this hill from 500m Twmpau to 500m Sub-Twmpau please click {here}

Myrddyn Phillips (July 2014)





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