Tuesday, 31 July 2018

Mapping Mountains – Significant Name Changes – 200m Twmpau


Foel Tyddyn y Berllan (SH 634 051)

There has been a Significant Name Change to a hill that is listed in the 200m Twmpau, with the summit height, drop and status of the hill being confirmed by a Trimble GeoXH 6000 survey which took place on the 14th May 2018.

The criteria for the list that this name change applies to are:

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub category entitled the 200m Sub-Twmpau consisting of all Welsh hills at or above 200m and below 300m 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 hill is adjoined to the Tarennydd range of hills which are situated in the south-western part of North Wales (Region A, Sub-Region A3), and it overlooks the Dyffryn Dysynni to its north-west, and has the small community of Abertrinant towards its east and Bryn-crug towards its south-west. 

Foel Tyddyn y Berllan (SH 634 051)

The hill appeared in the 200m P30 list on Geoff Crowder’s v-g.me website under the invented name of Bryn Tyddyn-y-berllan  with an accompanying note stating; Name from buildings to the North-East. 


Bryn Tyddyn-y-berllan
233m
124
23
Name from buildings to the North-East


During my early hill listing I thought it appropriate to either invent a name for a hill, or use a name that appeared near to the summit of the hill on Ordnance Survey maps of the day.  My preference was to use farm names and put Pen, Bryn or Moel in front of them.  This is not a practice that I now advocate as with time and inclination place-name data can be improved either by asking local people or by examining historic documents, through this form of research an appropriate name for the hill can usually be found.

When visiting this hill and adjoining hills I met a number of local farmers, including Stephen Jones who farms from Llanerch-goediog (SH 640 050), which is situated directly below the hill towards the east.  Stephen is aged 55 and a Welsh speaker and except for three years when in university he has lived at this farm all of his life.  We spent a number of minutes talking about the hills and their names, and two other names that Stephen also gave me will be documented in separate Significant Name Changes posts.  Stephen told me that this hill is a part of his land and that he knows it as Foel Tyddyn y Berllan.

Stephen Jones

I later met Joanne Redman on the summit of one of the hills that Stephen had given me a name for and she recommended that I speak with her father; Tomos Lewis, who Stephen also recommended me to contact.  I phoned Tomos and three days later visited him, when I pulled up he and Joanne were gathering sheep from a road-side pen and driving them up toward a field.

Tomos farms from Nant-y-mynach (SH 644 048) and is aged 60 and a Welsh speaker, he has lived at this farm since the age of six, having moved there from the council houses in Abertrinant.  During our conversations Tomos proved very knowledgeable and gave me many hill names that do not appear on any Ordnance Survey map, and one of them was the name of this hill; Foel Tyddyn y Berllan, which matches that given me by Stephen Jones.   

Tomos Lewis

Therefore, the name this hill is now listed by in the 200m Twmpau is Foel Tyddyn y Berllan and this name was derived from local enquiry.


The full details for the hill are:

Group:  Tarennydd

Name:  Foel Tyddyn y Berllan
 
Previously Listed Name:  Bryn Tyddyn-y-berllan
 
Summit Height:  232.8m (converted to OSGM15)

OS 1:50,000 map:  124

Summit Grid Reference:  SH 63481 05158 
 
Drop:  32.5m (converted to OSGM15)


The Trimble GeoXH 6000 gathering data at the summit of Foel Tyddyn y Berllan


Myrddyn Phillips (July 2018)










Monday, 30 July 2018

Mapping Mountains – Hill Reclassifications – The Fours


Citron Seat (NY 977 102) – 400m Sub-Four deletion

There has been a deletion from the listing of The Fours due to analysis of data on the OS Maps website, which is the recent replacement for OS Get-a-map.  The Fours is the title for the list of 400m hills of England and takes in all English hills at or above 400m and below 500m in height that have a minimum 30m of drop, the list is co-authored by Myrddyn Phillips and Aled Williams and the 2nd edition of the booklet containing this list was published by Mapping Mountains Publications on the 24th April 2018.

Accompanying the main list of The Fours are three categories of sub hills, with this hill being deleted from the 400m Sub-Fours.  The criteria for 400m Sub-Four status are all English hills at or above 400m and below 500m in height that have 20m or more and below 30m of drop. 
 
Prior to analysis of data on OS Maps this hill was listed with c 20m of drop based on the 446m summit spot height given to a triangulation pillar that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and an estimated col height of c 426m based on col contouring at 10m intervals and between 420m – 430m on the 1:50,000 Landranger and 1:25,000 Explorer maps.

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

The name of the hill is Citron Seat and it is situated in the Northern and Central Pennines and is placed in Region 35, Section 35A with its Cardinal Hill being Great Shunner Fell (SD 848 972).  The hill is positioned above the River Greta and the A 66 road which are to its north and the village of Bowes which is to its north north-east.

As the summit of the hill is a part of designated open access land it can be approached from a number of directions with a public footpath leading toward the summit from its north-east, however the shortest approach from a road is via a fence line from the north-west.

The deletion of Citron Seat from 400m Sub-Four status is due to the analysis of data on the OS Maps website.  This mapping gives contour intervals at 5m which has enabled the height of the col to be narrowed down when compared to the 10m contour intervals given on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps.  Therefore with a 446m summit spot height on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and an estimated col height of c 428m, based on col contouring on OS Maps between 425m – 430m, this hill is now listed with c 18m of drop, which is insufficient for its continued inclusion as a 400m Sub-Four.

Extract from OS Maps


The full details for the hill are:

Cardinal Hill:  Great Shunner Fell

Summit Height:  446m

Name:  Citron Seat

OS 1:50,000 map:  92

Summit Grid Reference:  NY 977 102

Drop:  c 18m


For the additions, deletions and reclassifications to The Fours reported on Mapping Mountains since the December 2013 publication of the list by Europeaklist please consult the following Change Registers:










Myrddyn Phillips and Aled Williams (July 2018)



Sunday, 29 July 2018

Mapping Mountains – Hill Reclassifications – 30-99m Twmpau


Ynys Ddu (SM 886 388) – 30-99m Twmpau addition

There has been confirmation of an addition to the 30-99m Twmpau list due to LIDAR analysis conducted by Myrddyn Phillips, with the criteria for this list being:

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m 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.

This hill did not appear in the main P30 list or the accompanying Hills to be surveyed sub list when the original Welsh P30 hills were published on Geoff Crowder’s v-g.me website as it was thought not to have 30m of drop and did not meet the criteria then used for the sub category; however this sub list has now been standardised including the addition of interpolated drop values and heights.

Ynys Ddu (SM 886 388).  Photo: Jon Glew

It was Mick Moore who brought the attention of this hill’s P30 status to the hill bagging community and prior to LIDAR analysis the hill was listed with an estimated summit height of c 32m based on a small 30m uppermost contour ring on Ordnance Survey 1:25,000 Explorer maps.

The name of the hill is Ynys Ddu and as its name implies it is an island, or more strictly speaking a tidal island that is attached to mainland Wales at low tide.  The hill is adjoined to the Mynydd Preseli group of hills, which are situated in the south-western part of Mid and West Wales (Region B, Sub-Region B4), with the island being positioned on the western part of Pen-caer (Stumble Head), and has the town of Abergwaun (Fishguard) towards the east south-east.

The summit of Ynys Ddu.  Photo: Jon Glew

If wanting to visit the hill permission to do so should be sought as it is not a part of designated open access land, for those wishing to do so caution is advised as the easiest approach will probably necessitate a scramble.

The confirmation of the addition of Ynys Ddu to 30-99m Twmpau status is due to LIDAR analysis conducted by Myrddyn Phillips.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

The 2m DSM LIDAR analysis gives the hill the following details:


Ynys Ddu

Summit Height:  31.9m

Summit Grid Reference:  SM 88673 38869

Bwlch Height:  0.5m

Bwlch Grid Reference:  SM 88721 38853

Drop:  31.3m


LIDAR image of Ynys Ddu

Therefore, the 31.9m LIDAR analysis for the summit position at SM 88673 38869 and the 0.5m LIDAR analysis for the bwlch position at SM 88721 38853 gives this hill 31.3m of drop, which is sufficient for 30-99m Twmpau status.


The full details for the hill are:

Group:  Mynydd Preseli

Name:  Ynys Ddu

OS 1:50,000 map:  157

Summit Height:  31.9m (LIDAR)

Summit Grid Reference:  SM 88673 38869 (LIDAR)

Bwlch Height:  0.5m (LIDAR)

Bwlch Grid Reference:  SM 88721 38853 (LIDAR)

Drop:  31.3m (LIDAR)


My thanks to Jon Glew for permission to reproduce his photos of Ynys Ddu

 Myrddyn Phillips (July 2018)





Saturday, 28 July 2018

Determining the position and height for the Great Rhos (SO 182 638) and Pegwn Mawr (SO 023 812) bylchau



The details between a hill’s summit and its critical bwlch are one that is seldom explored outside of being a list compiler or a surveyor.  This relationship is intrinsic to the hill, as it produces the drop value, which can be used as a part of the criteria for a hill’s classification.

For the uninitiated the critical bwlch is the point of least resistance when walking between summits or between valleys.  It is the lowest point reached when traversing from a hill’s summit to the next higher summit along the watershed.  When doing so, this point will also be the highest point reached when traversing between opposing valleys.

Also for the uninitiated; the drop value of the hill is the vertical height gain between the critical bwlch and the summit of the hill, with the caveat that each hill only has one critical bwlch, and no hill can share this point, therefore it is intrinsically linked to its respective hill’s summit.  However, the position of a hill’s critical bwlch can change and this is dependent upon its known height.

It is the last sentence above that is all important for the two hills that this article relates to; Great Rhos and Pegwn Mawr, as the listed height of each hill’s critical bwlch has been within 1m, and these critical points have also been swapped between the hills.  It was my aim today to finally determine which bwlch is higher and which is lower and therefore which bwlch is adjoined to Pegwn Mawr and which to Great Rhos.

Before detailing the survey result it may be prudent to briefly describe each hill and their position relating to one another and where each bwlch is also positioned.  I will also give brief details to their known heights and the history of their listed drop values.

Great Rhos is the highest hill in the Fforest Glud range of hills, which are also referred to as the Radnor Forest, it is positioned in the eastern part of mid Wales and has the small community of Maesyfed (New Radnor) and the A44 road to its south-east.

Pegwn Mawr is the highest hill in its own hill range and is also situated in the eastern part of mid Wales; it is positioned between the roads of the A470 to its north-west and the A483 to its east and has the towns of Llanidloes towards its west north-west and Y Drenewydd (Newtown) towards its north-east.

The two hills and their bylchau are orientated in a north-west direction, with the summit of Great Rhos being the most southerly, a northern traverse then bisects one bwlch which is positioned close to Llanbister Road Station, a north-westerly traverse then heads toward the summit of Pegwn Mawr, with a westerly traverse then bisecting the second bwlch which is positioned beside the A470 road and which has the town of Llanidloes towards its north-east and the small community of Llangurig towards its west.  Next higher ground is then to be found in the Pumlumon range of hills which are situated to the north-west of the second bwlch.

The main classification of each hill and their listed heights and the history of their listed drop values are given below:

Great Rhos and Pegwn Mawr have many classifications, two of which are Marilyn and Uchaf.  A Marilyn is a British hill that has 150m minimum drop irrespective of its height, with the list author being Alan Dawson.  An Uchaf is a Welsh hill that has a minimum height of 500m and minimum drop of 15m, with the list of Yr Uchafion co-authored by Myrddyn Phillips and Aled Williams.

When the listing of Marilyns was first published in 1992 in The Relative Hills of Britain book no drop values were given, although Great Rhos was later listed with an estimated c 373m of drop when The Hewitts and Marilyns of Wales booklet was published by TACit Tables in February 1997.  This drop value was based on a 660m map summit height and estimated bwlch height of c 287m.

Pegwn Mawr was listed in the TACit Tables booklet with 300m of drop based on a 586m map summit height and a bwlch height of 286m.

When the listing of Yr Uchafion was re-evaluated these drop values and the position of their respective bylchau were examined and as Great Rhos is the higher of these two hills it should be listed with the lowest of the two bylchau.  Therefore either the heights of the bylchau were incorrect or their positioning had been transposed. 

At the time of the re-evaluation of Yr Uchafion the Marilyns listing had been published on DoBIH (Database of British and Irish Hills), and at that stage I was working closely with two of the editors of DoBIH in a survey team, therefore I informed them that their positioning of these bylchau had been transposed, resulting in these bylchau then being swapped.  This re-evaluation resulted in the following details being given to these two hills:


DoBIH:

Great Rhos    660m summit at SO 18220 63902    286m bwlch height at SN 927 801, giving 374m of drop.

Pegwn Mawr    586m summit at SO 02394 81245    286m bwlch height at SO 178 717, giving 300m of drop.



Yr Ucahfion:

Great Rhos    660m summit at SO 18217 63896    c 285m bwlch height at SN 92702 80073, giving c 375m of drop.

Pegwn Mawr    586m summit at SO 02394 81245    c 287m bwlch height at SO 17837 71756, giving c 299m of drop.



The above resulted in DoBIH swapping the positions of the bylchau but listing them as the same height, whilst the Yr Uchafion list differentiated each bwlch by height.  I do not know if Alan Dawson as the Marilyns author was informed of this by DoBIH, I did not inform him at the time but have done so with the results of my survey with the Trimble GeoXH 6000.

Before detailing the survey results I will give a brief synopsis of each bwlch, as the surrounds of each has undergone intrusion by man and until recently it was not known how this had affected their respective heights, or if the natural bwlch still survived.  The latter point is important as it is generally accepted that if the natural bwlch of a hill is still intact even if a cutting reduces the height of the hill to hill traverse, then the height of the natural bwlch is taken as a part of the drop value of the hill.

When the positions of these bylchau were swapped list compilers were in the main reliant upon spot heights and the 10m contour intervals on contemporary Ordnance Survey 1:25,000 Explorer and 1:50,000 Landranger maps.  However, the series of Ordnance Survey Six-Inch maps were now available online and these include many benchmark and levelled heights which are more accurate than the beige spot heights that appear on contemporary maps. 

The Ordnance Survey Interactive Coverage Map hosted on the Geograph website was also now available and this enlarged mapping gave many spot heights not shown on any other publicly available map and the facility of producing a ten figure grid reference for any given position.

These two forms of mapping, one old and one new, helped in determining the height of each bwlch.  The southerly bwlch has two options for its critical point, both of which are between 280m – 290m in height on contemporary maps, one of these is placed near a gravel track that heads to a farm named Maylord, the other is placed on or beside a rail track which had been laid in a cutting on the eastern side of the bwlch surrounds.  An old benchmark helped in estimating the height of this bwlch, although it was not placed where the bwlch was considered to be positioned and therefore its height was not agreed, however there was consensus that its critical point was positioned near the track that leads to Maylord.

Extract from the Ordnance Survey 1:25,000 Explorer map for the bwlch of Great Rhos

The northerly bwlch has a disused railway cutting that bisects the surrounds of the bwlch in an east to west direction, with an elevated road that bisects this disused railway in a north-east to south-west direction, both have grazing fields on either side.  The 10m map contouring also gives this bwlch between 280m – 290m in height with contemporary Ordnance Survey 1:25,000 maps giving a 286m spot height on the road toward the north-east of the land that makes up that between the 280m – 290m contours, this spot height has been rounded up from a 285.3m and 285.5m (metric equivalent) height that appears on old Ordnance Survey base maps.  There are also a series of heights given to the old railway and road prior to when the rail bridge was demolished, however consensus could not be reached between the height or position of this bwlch, and the ones used by the then author of Yr Uchafion and DoBIH are quoted above.

Extract from the Ordnance Survey 1:25,000 Explorer map for the bwlch of Pegwn Mawr

Since the time when the position of these bylchau were swapped there has been dramatic changes in how such things are determined as people are now using the facility of Google cars to examine bylchau, and 5m contouring is now available on OS Maps, however the most revolutionary progress is that of LIDAR.

The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales, and this process has resulted in an almost endless stream of hill reclassifications.  With one of its major advantages being the facility to create coloured contouring at 0.001m intervals, this facility can be used to determine if natural bylchau still exist where intrusion by man has created either a road or railway that has been cut or elevated. 

As the southern bwlch was not covered by LIDAR the area was examined from the confines of a Google car and this quickly determined that the critical point was not placed beside the gravel track that leads to Maylord farm, as land from this point consistently went downhill toward the rail track on the hill to hill traverse.  This was substantiated by examining the 5m contours on OS Maps, this mapping has the bwlch position beside the gravel track leading to Maylord farm between 285m – 290m, whilst the bwlch on or beside the rail track is between 280m – 285m.

Extract from the 5m contouring on OS Maps

The northern bwlch is covered by LIDAR and extensive analysis determined that its critical natural point was intact and had not been obliterated either from the construction of the road or disused railway.  LIDAR analysis also determined that another natural bwlch still existed for this hill, but as this was higher on the hill to hill traverse it is not the critical point for this bwlch.  However, a lower point does exist on the hill to hill traverse and its position was determined by LIDAR analysis, but as this is placed in the remains of what is now an overgrown disused rail cutting it is the existing natural and critical bwlch that is taking precedence for determining the drop value.

LIDAR image for the bwlch of Pegwn Mawr with the joining of the white contours on bottom left the meeting of the valley to valley traverse if using the disused rail cutting, the near joining of the white contours in the centre of the image being the intact natural bwlch, and the meeting of the white contours toward the top right of the image being a remaining natural bwlch of the hill that has been slightly altered in recent times due to widening of access tracks

Two points were surveyed with the Trimble GeoXH 6000 at the southern bwlch, the first of which is where the 5m contouring on OS Maps place the critical bwlch, this is on the rail track.  OS Maps give the opposing valley to valley 280m contours to be positioned between SO 17712 71770 and SO 17871 71838, a mid-way point is conveniently placed where a gated track passes over the rail line, and this is where Trimble data were gathered from.

Approaching the bwlch of Great Rhos for the 1st survey

Gathering data at the bwlch of Great Rhos on the 1st survey

The second point surveyed at the southern bwlch is where the position of this bwlch had previously been listed, and this is beside the gravel track that leads to Maylord farm.  Visual confirmation that this is higher than the rail track substantiated examination of the land via a Google car and the 5m contouring on OS Maps.

Gathering data at the 2nd survey for the bwlch position of Great Rhos with the Trimble set up on top of my rucksack at the top of the gravel track leading to Maylord farm, and the rail track in the valley below to the right with a fence line indicating its position

The Trimble set-up position at the 2nd survey for the bwlch position of Great Rhos

Three points were surveyed with the Trimble GeoXH 6000 at the northern bwlch, the first of which is where LIDAR analysis places the natural critical bwlch, this is to the north of the A470 road and the disused rail cutting, and is placed in a grazing field.

Gathering data at the critical and intact natural bwlch of Pegwn Mawr during the 3rd survey (1st survey for Pegwn Mawr)

The second point surveyed is where LIDAR analysis places a remaining natural bwlch, but not the remaining natural bwlch, this is beside a gravelled track that has either been newly laid or widened, and therefore this ground has been recently disturbed by man.

Gathering data at a remaining natural bwlch, but not the remaining natural bwlch for Pegwn Mawr duting the 4th survey (2nd survey for Pegwn Mawr)

The third point surveyed is where LIDAR analysis places the high point of the valley to valley traverse that takes in the old disused rail cutting, this is also on the northern side of the A 470 road, and it is now overgrown and on the day I visited was being grazed by three cows.

Gathering data in the overgrown and disused rail cutting during the 5th survey (3rd for Pegwn Mawr)

The Trimble GeoXH 6000 results for each of these five surveyed points are given below:


1st survey:  281.3m at SO 17776 71803

2nd survey:  287.5m at SO 17877 71735

3rd survey:  285.9m at SN 92693 80074

4th survey:  286.7m at SN 92767 80103

5th survey:  283.8m at SN 92601 80035


As the natural point of the northern bwlch is intact and is higher (3rd survey) than the southern bwlch (1st survey), this northern bwlch should be adjoined to the lower hill; Pegwn Mawr (585.2m summit at SO 02394 81245).  This gives Pegwn Mawr 299.3m of drop.

As the southern bwlch (1st survey) is lower than the northern bwlch (3rd survey) this should be adjoined to the higher hill; Great Rhos (660m summit at SO 18217 63896).  This gives Great Rhos 379m of drop.


Myrddyn Phllips (July 2018)