Mapping Mountains – Trimble Surveys – Bannau Brycheiniog

13.09.19  Pen y Fan (SO 012 215), only bwlch surveyed

For many hill classifications the connection between the summit and bwlch of the respective hill is all important, as knowledge of each height gives the drop value of the hill.  This sounds simple, and usually in practice it is, however there are examples where the nature of the summit and that of the connecting bwlch come to the fore, and for Wales there are few other hills that can compare with Pen y Fan for the sometimes fraught nature of what constitutes a summit and also a bwlch.

Pen y Fan (SO 012 215)

Pen y Fan is the highest hill in south Wales and as such one can expect its connecting bwlch to the next higher summit to be a great distance from its high point, and this is so, with its bwlch situated towards the north close to or in the village of Talerddig.

For many years the summit of Pen y Fan had an Ordnance Survey triangulation pillar on its top.  Details in the OS Trig Database give a completion year of 1939; presumably this is when the pillar was installed.  The pillar was still in situ in 1990 but it was soon removed.  The summit of Pen y Fan now has a neatly arranged conical cairn at its high point, and adorning its top is a large upright flat rock with a fixed plaque giving the name and map height of the hill.  The old trig pillar had a flush bracket height of 886.358m and was set on a concrete base approximately 0.20m high, with natural ground at its base approximately 885.8m in height.

The trig pillar that once adorned the summit of Pen y Fan

I had visited and surveyed the summit of Pen y Fan on the 25^th October 2016, taking two data sets from the summit area, one at the top of the man-made conical cairn and the other on what I deemed to be the highest remaining natural ground of the hill.  These two data sets came to 885.739m at SO 01208 21582 and 884.601m at SO 01210 21587 respectively.  Dependent upon one’s view the 885.7m height from the top of the conical cairn can be taken as that for the hill as although the cairn is man-made it is nearer to the natural height of this hill when compared to the 884.6m height to remaining natural ground.  However, neither option is perfect.

Gathering data at the summit of Pen y Fan

Gathering data at the base of the man-made conical cairn at what can be deemed the remaining natural high point of the hill

The bwlch of Pen y Fan is to its north and placed close to, or in Talerddig, dependent again on one’s view of what constitutes a bwlch.  I had endeavoured to survey this bwlch on the 18^th August 2015 arriving in Talerddig early in the morning and proceeded to take a data set from where contour interpolation and an on-site inspection suggested the critical point to be positioned.  This point was in a field close to a house whose drive led toward the main road that passes through the village. 

Prior to data collection I had assessed the lay of land for a number of minutes, and had also done so after closing the equipment down and heading toward a gate which gave access to a drive leading to a house and which was beside the main road and a minor road where my car was parked.  When I reached the gate I looked back on my set-up position and wondered if it was correct, but with a big surveying day ahead that did not end until sunset I decided I was happy enough with the placement and headed south to examine the bwlch of Allt yr Esgair.

Gathering data at the 1st bwlch survey of Pen y Fan

Between then and now LIDAR has become available.  This has revolutionised hill classification in ways that those interested in such things could only dream of a few years ago.  Subsequently the bwlch of Pen y Fan was analysed via LIDAR by Aled Williams and the critical point was found to be beside the gate where I had looked back to the Trimble set-up position.

However, LIDAR also gives the opportunity to examine the lay of land in detail by building up contours at 1mm intervals if the inclination to do so takes a hold.  It also gives an opportunity to place accurate heights to such things as road and rail cuttings, something that contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps seldom do.  And just to add complication to an already fraught situation of what constitutes a summit and a bwlch, Talerddig just happens to have a rail cutting that when built was the deepest in the world.

LIDAR image of bwlch highlighted in white on right with the northerly part of the rail cutting highlighted in yellow on left

The rail line passing through Talerddig joined Machynlleth to Newtown and was constructed in the early 1860s.  The cutting is 37m deep (120ft) deep and must have been a difficult engineering task to complete.  Using LIDAR gives an opportunity to add an accurate height to this cutting as it makes its way southward up valley to the line’s high point before descending down valley toward Caersŵs.  The high point of the rail line to the south of the cutting would also be on the hill to hill traverse for anyone making their way from Pen y Fan to the next higher hill, and dependent upon one’s view should be taken in to account when calculating the drop value of this hill.  However, there’s no fundamental rights or wrongs with whether such things as cuttings should constitute a part of the drop value of a hill,  all one can do is assess the options and form an opinion, and if a different conclusion is formed by another person; respect it even though one may not agree with it.

LIDAR image of the rail cutting on left

LIDAR close up image of the rail line and the critical point of the bwlch highlighted in white

Therefore, we have a summit whose conical cairn is now man-made, although its height is nearer that of the natural height of this hill when compared to the highest remaining natural ground at the periphery of the conical cairn, and a bwlch that has a rail cutting which is lower on the hill to hill traverse compared to what may constitute the natural bwlch.  I say ‘may constitute the natural bwlch’ as when building up the contours with LIDAR I became aware that ground beside the house named Hafan that overlooks the field and gate where the Trimble GeoXH 6000 was previously set-up and where LIDAR places one position for the bwlch, looked as if it has been terra-formed as contours appear slightly ragged compared to their usual form.  The descending hill to hill contours also indicate that the bwlch should be placed near to where the Trimble was previously set up, although this is now on a descending route down valley from the gate where LIDAR places this option for the bwlch.  Having examined LIDAR in detail I concluded that the natural bwlch had been terra-formed and although a natural bwlch can still be followed up valley to ground at the base of the gate, the building of the house named Hafan had altered the lay of land sufficiently to disturb land where the natural bwlch was situated.

LIDAR close up image of the land leading to what could be deemed the remaining natural bwlch with the meeting of the white contour lines being the critical point; note jagged contours indicating the land has been terra-formed

Sometimes it is the surveying that is the simple task, with the dilemma of what constitutes a summit and bwlch being the difficult part.

Having surveyed what I thought to be the bwlch and with LIDAR indicating this option to be beside the gate I wanted to re-visit and as Talerddig was on route from the bwlch of Newydd Fynyddog which I had just surveyed to the bwlch of Aran Fawddwy which was my next port of call, I made my way over the hill road toward Talerddig. 

Having parked in the village, I walked the short distance to the gate with Trimble and surveying steps in hand and placed the Trimble atop the solid stone pillar adjacent to the gate and at the end of the drive leading to the house of Hafan.

The gate where LIDAR gives the remaining natural bwlch of Pen y Fan

I smiled as I looked over the gate toward where I had taken data from on my previous visit and quietly opened the gate to venture in to the field to take a measurement offset between the Trimble’s internal antenna and the ground in the field at its base.  Having noted a 1.51m offset I went back through the gate entrance, locked it behind me and stood on the surveying steps to set the file up in the Trimble, and once the 0.1m accuracy level was attained I pressed ‘Log’ and marched off toward the main road where I stood and took a few photos.

The Trimble set-up position at what can be deemed the remaining natural bwlch of Pen y Fan

Once the allotted data were gathered and stored I headed back to the surveying steps,  clambered up on them and pressed ‘Done’ and closed the equipment down, packed it away and headed back to my car, such a simple survey considering the complications of what constitutes the bwlch and summit of Pen y Fan. 

           

Survey Result:

Pen y Fan

Summit Height:  885.7m (converted to OSGM15, from previous Trimble GeoXH 6000 survey)

Summit Grid Reference:  SO 01208 21582

Bwlch Height:  215.0m (converted to OSGM15, remaining natural bwlch)

Bwlch Height:  209.3m (LIDAR, rail cutting)

Bwlch Grid Reference:  SH 93136 00074 (remaining natural bwlch)

Bwlch Grid Reference:  SH 93041 99532 (LIDAR, rail cutting)

Drop:  670.7m (cairned summit and remaining natural bwlch)

Drop:  676.45m (cairned summit and rail cutting bwlch)

Dominance:  75.72% (cairned summit and remaining natural bwlch)

Dominance:  76.37% (cairned summit and rail cutting bwlch)

  

For details on the summit survey of Pen y Fan

For details on the 1st bwlch survey of Pen y Fan

For further details please consult the Trimble Survey Spreadsheet

Mapping Mountains – Trimble Surveys – Bannau Brycheiniog and Fforest Fawr

25.10.16  Craig Gwaun Taf (SO 005 207), Pen y Fan (SO 012 215), Corn Du (SO 007 213), Y Gurn (SN 988 216) and Fan Fawr (SN 969 193, bwlch only)

Corn Du (SO 007 213)

I’d long wanted to visit the high peaks of Bannau Brycheiniog and Trimble them, and doing so was long overdue.  Having visited these and the other Welsh 2,000ft hills on many occasions, re-visiting them is always a pleasure, especially after time between visits being many years, when this happens it is a clichéd expression to say that it is like visiting old friends, but that is exactly how it feels, as although the hills are inanimate objects they have an uncanny presence that on many occasions can form characteristics seemingly all their own.

As well as wanting to visit the higher peaks of Bannau Brycheiniog there was one particular hill that I was extremely interested in Trimbling, this hill is Craig Gwaun Taf, which is an outlier of Corn Du and thrusts upward on its southerly ridge beyond Bwlch Duwynt before descending south-eastward toward the Pentwyn Reservoir.

Craig Gwaun Taf is given an 824m summit spot height on current Ordnance Survey maps and has bwlch contouring between 800m – 810m, with an 815m spot height on the area of the bwlch on the Ordnance Survey enlarged mapping on the Geograph website.  These figures give this hill an approximate c 13m of drop based on interpolation of bwlch contours, or only 9m of drop if based on the 815m spot height.  However, this hill and many others has recently been checked against LIDAR data by Joe Nuttall, who is the son of John and Anne Nuttall, who are guidebook authors and list compilers to the 2,000ft mountains of both England and Wales, and who have kept me busy on the hills for many a year.

LIDAR (Light Detection & Ranging) is highly accurate height data that is now freely available for much of England and Wales, and Joe has been diligently checking a number of hills for qualification to his parents 2,000ft list.  These lists are based on a minimum qualifying drop value of 15m and Joe found that LIDAR data gave Craig Gwaun Taf a drop of 15.783m, Joe then contacted me and asked if I could Trimble the hill.  By doing so it would give a comparison for this hill between LIDAR data and Trimble data, and confirm the hill’s drop value and unless the Trimble result was within an approximate 0.1m of the required minimum drop value of 15m it would also confirm the hill’s status.

I set off from the car park at the top of the A 470 opposite the Storey Arms at 8.50am, having driven from Worcester, the first time I’d ventured into Wales for a hill walk from the recesses of this remote part of deepest, darkest England.  Although the forecast gave settled, dry conditions with little breeze, the cloud base was low and a murky greyness pervaded the hills.

Deciding that I’d leave Y Gurn until later in the afternoon when its moorland path connecting it to the north-westerly ridge of Corn Du may be visible if the thickened layer of mist broke, as predicted, I walked south-eastward adjacent to the busy road on a gravelled track on the periphery of forestry to the car park at Pont ar Daf, this meant doing the higher peaks first, in mist, but as their paths are broad and their ridges easily discernible, route finding was not a problem.

I’d only been on the path from Pont ar Daf to Pen y Fan a couple of times before, once when cycling and pushing mountain bikes to its summit in 1990 during a ten day expedition mountain biking the hill boundary of Powys, on that day it was progressively getting hotter, which was a contrast to today, where when height was gained, a slight chill pervaded the wisps of mist as they gently rolled through the land.

The path at Pont ar Daf leading toward Craig Gwaun Taf, Corn Du and Pen y Fan

By the time I arrived at Bwlch Duwynt, which is the pass between Corn Du and Craig Gwaun Taf, one person had overtaken me and a few people had headed down the hill after making an early morning ascent, all were either heading toward or coming from Pen y Fan, leaving Craig Gwaun Taf quietly forgotten in the mist, which suited me and the Trimble just fine.

Today the critical bwlch consisted of an elongated, shallow muddy puddle which stretched over the bwlch from the valley to valley direction.  I checked the ten figure grid reference for the bwlch that Joe had given me when he assessed this hill’s drop via the LIDAR data, and chose a position within a few metres of this grid reference for the first of three Trimble positions at the bwlch.  This position was central on the valley to valley traverse and I gathered two five minute data sets from the same position.  I then collected a further five minute data set from either end of the shallow puddle, firstly on its western side and secondly on its eastern side.  These four data sets will give a good value for the height of this bwlch.

Gathering data at the bwlch of Craig Gwaun Taf

Gathering data at the first of three positions Trimbled at the bwlch of Craig Gwaun Taf

Having taken a number of photos I packed the Trimble away and headed to the summit of Craig Gwaun Taf, which I found was the second rise along the ridge when ascending from its connecting bwlch with Corn Du.  The summit consists of a small grassed hummock a couple of metres east of the path, which continues following the course of the hill’s south-easterly ridge.

I placed the Trimble on the high point and waited patiently for it to reach its 0.1m accuracy level before data should be logged, once one five minute data set was collected I switched the equipment off, then switched it back on and repeated the process until another five minute data set was gathered.  I then positioned the Trimble on top of my rucksack and measured a 0.23m offset between the high point of the hill and the Trimble’s internal antenna and waited until another five minute data set was gathered.  These three data sets will give a good value for the height of this hill and when combined with the four data sets taken at its bwlch, will give sufficient data to give Craig Gwaun Taf an accurate drop value and ascertain its status.

Looking north from the summit of Craig Gwaun Taf with the Trimble gathering data

Looking south from the summit of Craig Gwaun Taf with the Trimble gathering data

As I left the summit of Craig Gwaun Taf a number of voices cast from the mist and drifted my way in the slight breeze that occasionally sprang up, and by the time I reached the path toward Pen y Fan a multitude of people were heading in all directions, some downward, others up towards Corn Du and more toward Pen y Fan, I suspected the summit of south Wales’ highest mountain may be a little busy.

Glimpsing Corn Du through the mist

The summit of Pen y Fan once had a trig pillar at its high point, nowadays it has a constructed cairn with an embedded stone marker giving the hill’s name and height, and it also has many visitors who throng to its summit in all weathers.  When I arrived I wondered how on earth I was going to keep so many people away from the high point when the Trimble was gathering its all-important summit data.  Surprisingly this proved relatively easy and I only had to explain to a few people what I wanted to do and all were extremely compliant with the wants of a mountain surveying Trimbling person.

The Trimble holding back the multitude as it gathers data at the summit of Pen y Fan

Having gathered data at the top of the solid cairn I wanted another five minute data set at the highest land at the periphery of the cairn, this again proved relatively easy to obtain. 

Gathering data at the high point on the periphery of the summit cone

Gathering data adjacent to the coned cairn atop Pen y Fan

Leaving the throng of people beside the summit of Pen y Fan I back-tracked to its connecting bwlch with Corn Du, the position of this bwlch proved easy to identify, and within a few minutes the Trimble was balanced over the northern precipice gathering data.

Gathering data at the critical bwlch of Corn Du

My next objective was Corn Du and I hoped that its summit would give a little peace and quiet when compared to that of Pen y Fan, however it didn’t want to be outdone by its higher neighbour and another multitude of people were gathered around its constructed cairn.  This summit also proved relatively easy to survey as everyone gathered around its periphery giving the Trimble time and space to gather its data.  Before heading down the north-westerly ridge of Corn Du I wanted another five minute data set from the highest natural ground remaining on the hill, I judged this to be one of the small grass hummocks on the edge of its very steep northerly drop, I placed the Trimble on it and secured it in place with a few small rocks before pressing ‘Log’ and hoping that it wouldn’t fancy a quick descent in to the cwm 250m – 300m below.

Gathering data at the summit of Corn Du

Gathering data at what I judged to be the remaining 'natural' high point of Corn Du

Once the Trimble was salvaged from its precarious position I plodded down in continuing mist, following the broad path to the obelisk commemorating Tommy Jones, who at the age of five lost his way from Cwm-llwch farm and whose body was found on this spot 29 days later.  I knew that a path went from near this obelisk toward the bwlch and then the summit of my last hill of the day; Y Gurn, but I also knew that the path was relatively narrow and that other paths probably existed heading off in a number of directions.  Finding one that took me onward I happily followed it until it seemed to be heading too far south, I stopped and checked the grid reference in the Trimble against the map and back-tracked across the moor until at the critical bwlch of Y Gurn, by now the misty conditions that had pervaded the hills started to break up and sunlight pierced out from behind the cloud, brightening the land and giving a partly hazed autumnal glow.

After gathering data at the critical bwlch of Y Gurn I followed a good path to its summit and placed the Trimble beside the small cairn that sits atop a peat hagged hummock, once the customary five minutes of data were gathered I followed the path and fence line down to connect with the main path that heads from Storey Arms to Pen y Fan.

Gathering data at the critical bwlch of Y Gurn

Gathering data at the summit of Y Gurn

There were many people on this main path, with the majority heading down to the Storey Arms, but some were heading up in what was proving to be brightening conditions with glimmers of the higher peaks tantalisingly on show as their straight edged ridges gleamed out of the cloud.

Craig Gwaun Taf above afternoon mist with people heading back to the Storey Arms on the main Pen y Fan path

Only one survey remained and that was for the critical bwlch of Fan Fawr which proved to be adjacent to the car park opposite the Storey Arms.  This was on ground next to a ditch which I followed in both directions, and which seemed to be continuous and therefore probably man-made for drainage, because of this I chose a spot that was conveniently on solid ground above the ditch beside one of the duck boards laid across it, once five minutes of data were collected I headed back to my car happy in the knowledge that 15 surveys had been conducted and that the status of Craig Gwaun Taf would be finally determined.

Gathering data at the critical bwlch of Fan Fawr

Survey Result:

Craig Gwaun Taf

Summit Height:  826.4m (converted to OSGM15) (significant height revision) 

Summit Grid Reference:  SO 00548 20720

Bwlch Height:  810.3m (converted to OSGM15)

Bwlch Grid Reference:  SO 00555 20862

Drop:  16.1m (Uchaf addition confirmed and Nuttall addition confirmed)

Dominance:  1.95%

 

Pen y Fan

Summit Height:  885.7m (converted to OSGM15)

Summit Grid Reference:  SO 01208 21582

Bwlch Height:  215.0m (converted to OSGM15, from subsequent Trimble GeoXH 6000 survey to remaining natural bwlch)

Bwlch Height:  209.3m (LIDAR, disused rail cutting)

Bwlch Grid Reference:  SH 93136 00074 (remaining natural bwlch)

Bwlch Grid Reference:  SH 93041 99532 (LIDAR, disused rail cutting)

Drop:  670.7m (cairned summit and remaining natural bwlch)

Drop:  676.45m (cairned summit and disused rail cutting bwlch)

Dominance:  75.72% (cairned summit and remaining natural bwlch)

Dominance:  76.37% (cairned summit and disused rail cutting bwlch)




Corn Du

Summit Height:  872.6m (converted to OSGM15)

Summit Grid Reference:  SO 00718 21332

Bwlch Height:  843.6m (converted to OSGM15)

Bwlch Grid Reference:  SO 00911 21394

Drop:  29.0m (Subsimm and 800m Sub-Twmpau status confirmed)

Dominance:  3.32%

 

Y Gurn

Summit Height:  618.9m (converted to OSGM15)

Summit Grid Reference:  SN 98895 21607

Bwlch Height:  591.5m (converted to OSGM15)

Bwlch Grid Reference:  SN 99173 22100

Drop:  27.4m (Subsimm and 600m Sub-Twmpau status confirmed)

Dominance:  4.42% 
 

Fan Fawr

Summit Height:  734m (spot height)

Summit Grid Reference:  SN 96997 19351 (spot height)

Bwlch Height:  439.5m (converted to OSGM15, Trimble GeoXH 6000)

Bwlch Grid Reference:  SN 98223 20289 (Trimble GeoXH 6000)

Drop:  295m (spot height summit and Trimble GeoXH 6000 bwlch)

Dominance:  40.13% (spot height summit and Trimble GeoXH 6000 bwlch)

 

For details on the 1st bwlch survey of Pen y Fan

For details on the 2nd bwlch survey of Pen y Fan

For further details please consult the Trimble Survey Spreadsheet

Mapping Mountains – Trimble Surveys – Bannau Brycheiniog

18.08.15  Pen y Fan (SO 012 215), only bwlch surveyed 

The bwlch of this hill has been surveyed for a second time with the details at the end of this post from this survey, with the text below remaining for historic merit    

The bwlch of Pen y Fan

There can be a perverse sense of fulfilment and enjoyment in surveying bylchau, this is not something that is always evident when tackling summits.  Although the high point of a hill can sometimes be found in the most unusual of places, bylchau are prone to be situated in land that can be thought of as rather esoteric.

There’s also the added excitement of making forays onto ground that is private, permission to do so should of course be sought, but occasionally circumstance necessitates a clandestine visit, assessing the ground as quickly and as accurately as time allows and getting back onto the relative safety of common or public ground as quickly as possible.

A number of today’s bylchau fitted the scenario as outlined above, with the first and the only one this blog post deals with, in a field on the outskirts of Talerddig, which is situated beside the A470 between Caersws and Glantwymyn (Cemmaes Road).

Depending upon one’s inclination this particular bwlch is one of two that are the most important in Wales, as it spits the Regional mass of North Wales from that of Mid and West Wales.  This point is also the critical bwlch for Pen y Fan, and the association between summit and critical bwlch can also be rather perverse as in this instance the former is the highest point in South Wales and dominates the skyline with its distinctive profile, whilst the latter is almost forgotten except by the occasional passing bwlch connoisseur who enjoys this kind of thing!

The critical bwlch of Pen y Fan can be found in a field on the outskirts of the small community of Talerddig, which according to many on-line entries is a small village in Mid-Wales, however topographically the village is split between the Regions of North Wales and that of Mid and West Wales.  This Regional split will be detailed in a later blog post and will form an intrinsic part of a hill list co-authored with Aled Williams. 

The area of this critical bwlch has a 218m spot height at SH 93198 00039 on Ordnance Survey maps, this spot height is placed on the A470.  Centralising the hill to hill contours suggests that the critical bwlch is placed just to the south of this road; this is backed up by driving around the area in a Google Car which suggests that the critical bwlch is placed somewhat below this road to the south in a field.  The bwlch area also has a railway cutting to its west; this cutting is substantial and formed part of the line between Newtown and Machynlleth, which was closed during the Beeching cuts.  This cutting is 37m (120ft) deep and when completed in 1862 it was the deepest railway cutting in the world, but as I was looking for the natural bwlch the old railway line and its cutting could wait for another day for a person a little more adventurous than me.

I set off relatively early from Welshpool and once in Talerddig I parked just off the A470 and walked back up the road to examine the lay of the land.  A quick inspection confirmed what I had seen when whizzing around in the Google Car as the ground fell away from the road to its south.  However, once in one of the fields I wondered where exactly the critical bwlch lay as there was a vegetated water channel running the length of a near hedge and a land bridge of earth and grass crossing it to gain access into the adjacent field through a gate.  The land then continued toward a house, it was this land that formed part of the valley to valley traverse, as with most bylchau the hill to hill traverse is relatively easy to ascertain but the valley to valley traverse can be problematic to pinpoint when doing so without the aid of an optical implement and a grid of flags.

Between me and the house was a hedge, gate and another open field with very little coverage to camouflage proceedings, thankfully the bedroom curtains of the house were still closed, so I went about my business as quickly and quietly as I could, it seemed that the valley to valley highpoint was through the gate and in the adjacent field, so within a couple of minutes I had positioned the Trimble on top of my rucksack and measured a 0.44m offset between the ground at its base and the internal antenna in the Trimble.  Before starting to log data I wandered up the field to assess the lay of land from a different direction, happy with the Trimble’s placement I pressed ‘Log’ and it started gathering data.

The Trimble GeoXH 6000 placed were I deemed the critical bwlch of Pen y Fan to be situated

The view down the field toward the Trimble with the continuation of the hill to hill traverse toward the mast in the background and on the left of this photograph

During the time that the Trimble gathered data I stood behind a hedge in the opposing field and hoped the bedroom curtains would not be thrown open for the occupant to be confronted by a mysterious blue rucksack that had an equally mysterious yellow and black object perched on top of it.  Thankfully by the time that five minutes of data were collected the village still remained quiet and I packed the equipment away and walked back up the field and onto the road.

I just hoped that the bedroom curtains weren't going to open

As I headed towards my car I looked back across the field toward where the Trimble had been placed, the adjacent house was now almost directly in front of me and the lay of land seemingly gently rising up part of the valley to valley traverse to the position where the Trimble had been placed, happy with the morning’s activities I got back into my car and drove south to examine the second of these Regional bylchau.

Looking back to the Trimble set-up position

Survey Result:

Pen y Fan

Summit Height:  885.7m (converted to OSGM15, from subsequent Trimble GeoXH 6000 survey)

Summit Grid Reference:  SO 01208 21582

Bwlch Height:  215.0m (converted to OSGM15, from subsequent Trimble GeoXH 6000 survey to remaining natural bwlch)

Bwlch Height:  209.3m (LIDAR, disused rail cutting)

Bwlch Grid Reference:  SH 93136 00074 (remaining natural bwlch)

Bwlch Grid Reference:  SH 93041 99532 (LIDAR, disused rail cutting)

Drop:  670.7m (cairned summit and remaining natural bwlch)

Drop:  676.45m (cairned summit and disused rail cutting bwlch)

Dominance:  75.72% (cairned summit and remaining natural bwlch)

Dominance:  76.37% (cairned summit and disused rail cutting bwlch)

For details on the summit survey of Pen y Fan

For details on the 2nd bwlch survey of Pen y Fan

For further details please consult the Trimble survey spreadsheet click {here}