Mapping Mountains – Hill Reclassifications – 700m Twmpau

700m Twmpau – Hill Reclassifications

The 700m Twmpau (thirty welsh metre prominences and upward) are the Welsh hills at or above 700m and below 800m in height that have a minimum drop of 30m.  Accompanying the main P30 list is a sub list entitled the 700m Sub-Twmpau with the qualification to this sub category being all Welsh hills at or above 700m and below 80om 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 - 700m Twmpau

Pt. 714.3m (SH 827 359) – 700m Sub-Twmpau addition (5th reclassification)

Significant Height Revisions post for Pt. 714.3m

There has been an addition to the listing of the 700m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Aled Williams. 

LIDAR image of Pt. 714.3m (SH 827 359)

The criteria for the list that this addition applies to are:

700m Twmpau - Welsh hills at or above 700m and below 800m in height with 30m minimum drop, with an accompanying sub list entitled the 700m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 700m and below 800m in height with 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 and is available to download in Google Doc format from Mapping Mountains.

The 700m Twmpau by Myrddyn Phillips

The hill is being listed by the point (Pt. 714.3m) notation and it is adjoined to the Arenig Fawr group of hills, which are situated in the central part of North Wales (Region A, Sub-Region A2), and it is positioned with a minor roads to the north, south-west and east, and the A4212 road farther to its north, and has the town of Y Bala towards the east.

When the list that later became known as the 700m Twmpau was first compiled, this hill was not included in the accompanying sub list due to an eye and spirit level survey conducted by John and Anne Nuttall that resulted in 60ft (18.3m) of drop, and it was originally listed with a 712m summit height based on the spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and a 694m bwlch height. 

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

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales.

Therefore, the addition of this hill to 700m Sub-Twmpau status is due to LIDAR analysis, resulting in a 714.3m summit height and a 693.6m bwlch height, with these values giving this hill 20.7m of drop, which is sufficient for it to be classified as a 700m Sub-Twmpau.

 

The full details for the hill are:

Group:  Arenig Fawr

Name:  Pt. 714.3m

OS 1:50,000 map:  124, 125

Summit Height:  714.3m (LIDAR) 

Summit Grid Reference:  SH 82741 35938 (LIDAR) 

Bwlch Height:  693.6m (LIDAR) 

Bwlch Grid Reference:  SH 82725 36128 (LIDAR) 

Drop:  20.7m (LIDAR)

 

Myrddyn Phillips (July 2023)

 

Mapping Mountains - Hill Reclassifications - 700m Twmpau

Pen y Gadair Fawr (SO 229 287) – 800m Twmpau reclassified to 700m Twmpau (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 listed in the 800m height band of P30 Twmpau hills and it has now been reclassified to a 700m Twmpau.

The criteria for 700m Twmpau status is all Welsh hills at or above 700m and below 800m in height with 30m minimum drop, whilst the criteria for 800m Twmpau status is all Welsh hills at or above 800m and below 900m in height with 30m minimum drop.  Details to the 700m Twmpau were published on Mapping Mountains on 15^th April 2015, and details to the 800m Twmpau were published on Mapping Mountains on the 15^th March 2015.

The name of the hill is Pen y Gadair Fawr and it had been listed in the 800m height band of Twmpau hills, based on the 800m summit spot height that appears on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps.  With the 800m height on Ordnance Survey maps originating from the 2624ft (799.8m) imperial bench mark height on the series of old Six-Inch maps.

The hill is situated on one of the central ridges that forms the Mynyddoedd Duon (Black Mountains) group of hills with its Cardinal Hill being Waun Fach (SO 215 299) and is placed in the Region of South Wales (Region C, Sub-Region C3).  It is situated between the steam valleys of the Grwyne Fawr to its north-east and the Grwyne Fechan to its south, with the town of Talgarth towards the north-west and Y Gelli Gandryll (Hay-on-Wye) towards the north.

As the hill is a part of designated open access land it can be accessed from most directions, however an extended circular walk taking in the ridge upon which it is positioned in conjunction with the ridge to its west is a good way to accustom oneself with this hill range.

The reclassification of Pen y Gadair Fawr to 700m 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:

Pen y Gadair Fawr

Summit Height:  799.8m

Summit Grid Reference:  SO 22944 28758

Bwlch Height:  753.2m

Bwlch Grid Reference:  SO 22657 29359

Drop:  46.6m

Therefore, the 799.8m LIDAR data produced for the summit position at SO 22944 28758 and the 753.2m LIDAR data produced for the bwlch position at SO 22657 29359 gives this hill 46.6m of drop, and as the summit height is below 800m it is reclassified to a 700m Twmpau with a 799.8m summit height.

This now revises the total in the 800m and 700m Twmpau which will be updated accordingly.

The full details for the hill are:

Cardinal Hill:  Waun Fach

Summit Height:  799.8m (LIDAR data)

Name:  Pen y Gadair Fawr

OS 1:50,000 map:  161

Summit Grid Reference:  SO 22944 28758
  

Drop:  46.6m (LIDAR data)

Pen y Gadair Fawr (SO 229 287) now reclassified from an 800m Twmpau to a 700m Twmpau

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

Myrddyn Phillips (October 2017)

Mapping Mountains - Hill Reclassifications - 700m Twmpau

Craig Eigiau (SH 713 654) – 700m Sub-Twmpau addition (3rd reclassification)

Survey post for Craig Eigiau

There has been an addition to the Twmpau (thirty welsh metre prominences and upward)  list due to a survey with the Trimble GeoXH 6000, and a subsequent survey by Alan Dawson with the Leica RX1250, with this hill being included in the 700m Sub-Twmpau.  Accompanying all the 100m height band of hills within the Twmpau are sub lists with the one attached to this list being entitled the 700m Sub-Twmpau. 

The criteria for 700m Twmpau status is all Welsh hills at or above 700m and below 800m in height with 30m minimum drop, the criteria for 700m Sub-Twmpau status is all Welsh hills at or above 700m and below 800m 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 15^th April 2015.

Prior to the survey with the Trimble GeoXH 6000 the summit of this hill had been analysed with LIDAR data by Aled Williams, resulting in a 733.9m height, and it had remained listed as an Uchaf with an estimated c 19m of drop based on the 735m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger map and the 1:25,000 Explorer map, with an estimated bwlch height of c 716m based on bwlch contouring between 710m – 720m. 

The name of the hill is Craig Eigiau and it is situated in the Carneddau group of hills and is placed in the Region of North Wales (Region A, Sub-Region A1) with its Cardinal Hill being Carnedd Llywelyn (SH 683 643).  The hill is positioned between two reservoirs; Melynllyn to its west and Llyn Eigiau to its east, with the small community of Tal-y-bont to the north-east of the hill, and it can be visited via its northern ridge which can be gained from a track leaving the high car park close to Llyn Eigiau, however it is more rewarding to combine this hill in a longer walk with a number of its higher neighbours.

The survey with the Trimble produced a summit height of 734.7m (converted to OSGM15) at SH 71314 65425 and a bwlch height of 713.9m (converted to OSGM15) at SH 71185 65473, with these values giving this hill 20.8m of drop, with the details from the Leica RX1250 survey conducted by Alan Dawson being 735.0m (converted to OSGM15) summit height at SH 71315 65425 and 714.1m (converted to OSGM15) bwlch height at SH 71191 65460, with these values giving this hill 20.9m of drop, which is sufficient for its addition to 700m Sub-Twmpau status.  This now revises the total in the 700m Twmpau which will be updated accordingly.

The full details for the hill are:

Cardinal Hill:  Carnedd Llywelyn

Summit Height:  735.0m (converted to OSGM15, Leica RX1250)

Name:  Craig Eigiau

OS 1:50,000 map:  115

Summit Grid Reference:  SH 71315 65425 

  

Drop:  20.9m (converted to OSGM15, Leica RX1250)

The overall total for the 700m Twmpau remains at 32 hills with two reclassifications to 700m Sub-Twmpau status since publication of this list on the Mapping Mountains site on 15^th April 2015.

The overall total for the 700m Sub-Twmpau is now 7 hills with two reclassifications from 700m Twmpau status and one addition since publication of the list on the Mapping Mountains site on 15^th April 2015.

The list of 700m Twmpau is available from Mapping Mountains (April 2015) with all subsequent changes detailed in the 700m Twmpau – Hill Reclassifications on the Mapping Mountains site.

The Trimble GeoXH 6000 gathering data at the summit of Craig Eigiau

For details on the survey that confirmed this hill’s 700m Sub-Twmpau status

Myrddyn Phillips (July 2017)

Mapping Mountains - Hill Reclassifications - 700m Twmpau

Fan y Big (SO 036 206) - 700m Twmpau reclassified to 700m Sub-Twmpau (2nd reclassification)

1st survey post for Fan y Big

2nd survey post for Fan y Big

Significant Height Revisions post for Fan y Big

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 listed in the 700m height band of P30 Twmpau hills and it has now been reclassified to a 700m Sub-Twmpau, with the criteria for the sub hills being 700m or more and below 800m 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 15^th April 2015.

The hill had been listed with 30m of drop, based on the 719m summit spot height that appears on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps and the 689m bwlch spot height that appears on the Ordnance Survey enlarged mapping hosted on the Geograph website. 

The hill is situated in the central part of the main ridge that forms 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 (Region C, Sub-Region C2).  It is situated between the towns of Aberhonddu (Brecon) to its north and Merthyr Tudful to its south.

The hill can be accessed from public footpaths originating from its north and from its south; or it can be combined as a longer expedition taking in the main Bannau Brycheiniog ridge either from its west or from its east.

The name of the hill is Fan y Big and its reclassification to a 700m Sub-Twmpau 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:

Fan y Big

Summit Height:  716.3m

Summit Grid Reference:  SO 03651 20662

Bwlch Height:  688.1m

Bwlch Grid Reference:  SO 03773 19876

Drop:  28.2m

Therefore, the 716.3m LIDAR data produced for the summit position at SO 03651 20662 and the 688.1m LIDAR data produced for the bwlch position at SO 03773 19876 is sufficient for this hill to be reclassified from a 700m Twmpau to a 700m Sub-Twmpau with 28.2m of drop.

This now revises the total in the 700m Twmpau which will be updated accordingly.

The full details for the hill are:

Cardinal Hill:  Pen y Fan

Summit Height:  716.3m (LIDAR data)

Name:  Fan y Big

OS 1:50,000 map:  160

Summit Grid Reference:  SO 03651 20662 

  

Drop:  28.2m (LIDAR data)

Fan y Big (SO 036 206) now reclassified to a 700m Sub-Twmpau

My thanks to Aled Williams for analysing the details of this hill

For details on the first survey of Fan y Big

For details on the second survey of Fan y Big

Myrddyn Phillips (March 2017)

Mapping Mountains - Hill Reclassifications - 700m Twmpau

Bera Mawr (SH 674 682) - 700m Twmpau reclassified to 700m Sub-Twmpau (1st reclassification)

Survey post for Bera Mawr


There has been a reclassification to the 700m Twmpau (thirty welsh metre prominences and upward) list due to a survey with the Trimble GeoXH 6000, with a subsequent survey having been conducted by Alan Dawson using a Leica RX1250.   The hill is situated in the north-western part of the Carneddau in Eryri, and is positioned south of Llanfairfechan and eastward of Bethesda.

These details are retrospective as the Trimble GeoXH 6000 survey that resulted in the reclassification of this hill from 700m Twmpau to 700m Sub-Twmpau status was conducted on 10^th March 2014 on a bright early spring day.

The hill is relatively remote for a Welsh hill and it can be accessed from above Abergwyngregyn to the north, or from the upper parts of Bethesda to the west or from the main Carneddau ridge to its south-east.  Most approaches enable the walker to visit other hills on the way.

The hill is named Bera Mawr and its summit is positioned at SH 674 682.  The hill was listed with c 31m of drop based on a 794m summit spot height and an estimated bwlch height of c 763m.  The area of the bwlch is comprised of relatively short grass and the set-up position of the Trimble for the bwlch survey was given a 0.3m margin of uncertainty for height.

The survey with the Trimble GeoXH 6000 resulted in a 793.6m (converted to OSGM15) summit height with Estimated Accuracies of 15-30cm: 55.22%, this figure is below the average and therefore it would be favourable for this hill to be revisited and another data set gathered for comparison.  The bwlch survey resulted in a 763.9m (converted to OSGM15) height and the normal Estimated Accuracies of 5-15cm: 100.00%.  The survey conducted by Alan Dawson resulted in a 793.69m (converted to OSGM15) summit height at SH 67482 68271.

This now brings the overall total for the hills listed in the 700m Twmpau to 33 and the total for the 700m Sub-Twmpau to 5,  please click {here} to access the list and {here} for its detailed Introduction.

The full details for the hill are:

Cardinal Hill:  Carnedd Llywelyn

Summit Height:  793.7m (converted to OSGM15, Leica RX1250)

Name:  Bera Mawr

OS 1:50,000 map:  115

Summit Grid Reference:  SH 67482 68270

Drop:  29.8m (converted to OSGM15, Leica RX1250 summit and Trimble GeoXH 6000 bwlch)

Gathering data at the summit of Bera Mawr, which resulted in this hill being reclassified from a 700m Twmpau to a 700m Sub-Twmpau

For details on the survey that reclassified this hill from 700m Twmpau to 700m Sub-Twmpau status please click {here}

Myrddyn Phillips (March 2014)