Mapping Mountains – Trimble Surveys – Yr Wyddfa

07.07.26  Yr Wyddfa (SH 609 543, only bwlch surveyed)

The Trimble GeoXH 6000 and Leica Gs15 gathering data at the summit of Yr Wyddfa

In September 2014 along with Graham Jackson and John Barnard I surveyed the summit of Yr Wyddfa.  In attendance was Mark Greaves representing Ordnance Survey.  It was Mark who later processed the gathered data.  Our endeavours were filmed by Stephen Edwards of Cread Cyf and Aled Llŷr, with the film appearing on ITV Wales.

The summit architecture of Yr Wyddfa has changed over many years, with all manner of structures being built.  These have consisted of huts where horses were stabled and the Victorian tourists who ascended on them could rest, take in the view, if indeed one existed and recover from their exploits before the journey back down the mountain.

Over time huts evolved in to a hotel and latterly a summit café.  However, these constructions did not limit themselves to the ground surrounding the summit, they also took in the summit itself, with massive cairns of stone, a flag pole and latterly a summit plinth with a weather station and identification plague on top of what is fashioned to resemble a triangulation pillar.  This stands atop the aforementioned plinth which has been constructed over the natural summit tor.  Thankfully we have a bench mark height to the bedrock which can supposedly still be accessed from a small window on the side of the weather station.  It was the wisdom of Ordnance Survey who installed the bench mark and documented its height, as all we could do when resurveying the summit of Yr Wyddfa was take a measurement to the concrete plinth, which is an obvious man-made addition to the height of the mountain.

As with many listings, the qualification whether a hill should be included is dependent upon its drop.  This is the height difference between its summit and bwlch that connects to the next higher summit along its watershed.  The approximate position of the Yr Wyddfa bwlch had been known for many years and to my knowledge was first documented by Alan Dawson.  This connecting bwlch is positioned beside the Forth and Clyde canal in Scotland.

The Ordnance Survey give a 46m spot height on the 1:25,000 Explorer map at NS 76804 78578, which could be where the critical point of this bwlch is positioned.  However, map study shows two burns descending southward from the hillside above the small community of Kelvinhead.  As these two burns near the canal one heads westward and the other eastward, suggesting that the bwlch is positioned on ground between the two.  This is the best available evidence we have at the moment for the position of this bwlch, until LIDAR becomes available for this part of the country.

This was a survey I had wanted to do for many years, but opportunity was limited as I now rarely venture north in to Scotland.  However, with an offer to stay accompanied by John Kirk, in Mark Trengove and his wife’s newly built second home in Laide in Wester Ross, this gave us the prospect to survey this bwlch on our way north.

Arriving at Mark’s at midday we quickly packed my gear in his car and he then proceeded to drive to John’s in Burnley where we over-nighted before John took over the driving duties heading north.  As the hours of travel slowly ticked by the weather became more inclement with fine drizzled spots of rain hitting the windscreen.  By the time we left the M80 and drove in to Kelvinhead the sky was coloured light grey and light rain interspersed with more drizzle met us as I quickly got my walking boots on for the walk down to the canal. 

Heading down the path toward the bwlch

John seemed to know this area well and we followed him toward the gate giving access to the narrow path leading down beside what turned out to be one of the burns, which only showed its watery trickle as we approached the canal.  This burn was on our right as we descended, whilst the burn on our left was no more than a slight indentation consisting of lots of greenery, which as least intimated that water was in fact present. 

Nearing the bwlch

A gate gave further access to the canal towpath, and it was close to this gate where the majority of our efforts were concentrated, as all ground on the path descended to this point and beyond the gate all ground went uphill for a short distance to the canal towpath.  On our way through the gate we had a quick discussion where we considered the critical point to be positioned.  We then visited the canal which was unexpectedly wide at this point.  The surprise at its width was based on the experience of my local Montgomeryshire canal where two narrow boats crossing would be the limit; this canal was like a river.  However, John later explained that this part consisted of a water basin where boats could pass without difficulty. 

Arriving on the canal towpath

We stood beside the water for a number of minutes with John pointing out the ditch on the far side of the canal.  If whilst on the valley to valley traverse the height of a cutting was taken as the critical point of the bwlch, the ditch formed a major difficulty in our endeavours as from this vantage point it looked lower on the hill to hill traverse, but again John explained that breaking the ditch is a bank that goes in the hill to hill direction, thus increasing the high point of the valley to valley traverse if following the ditch.  Therefore, it seemed we were safe in taking the ground close to the gate as the critical point for the bwlch of Yr Wyddfa. 

The western view of the canal

Looking south on the hill to hill traverse with the ditch evident adjacent to the opposing bank

The eastern view of the canal

Once a few photos of the canal were taken we backtracked to the gate and had a good inspection of the path and its downward passage toward this point.  We initially considered gathering data from the ground immediately through and at the base of the gate, but soon the Trimble was moved to the path leading toward the gate.  Ground hereabouts within a ten metre distance looked consistently flattish and with little margin of uncertainly for such a survey the Trimble was quickly positioned on my rucksack, which in instances like this forms a convenient makeshift tripod.  Once the 0.1m accuracy level was attained before data should be logged, I pressed ‘Log’ and headed back through the gate to stand away from the equipment as it gathered its customary five minutes of data. 

The Trimble GeoXH 6000 gathering data at the bwlch of Yr Wyddfa

After data were gathered and stored I closed the equipment down and took a series of photos from various directions of the Trimble in situ.  It was then packed away and we headed up the path toward the dry confines of John’s car.  On the way we met David Henderson on his quad bike with three attendant sheep dogs scampering after him.  I flagged him down for a chat. 

The northern view from the bwlch

The eastern view from the bwlch

The southern view from the bwlch

The western view from the bwlch

We spent a number of minutes with David; he told us he’s known as Dov by all his friends.  I happily explained the significant of the land he farms and specifically the point on the path no more than five minutes down from where we were now standing.  He didn’t look amazed, which was a disappointment and seemed to take in the critical nature of this point in his stride.  Aw well! 

The view further east

David Henderson with Bessie, Roy and Peggy

Leaving the bwlch

After leaving David we continued on the slight uphill leading back to the houses in Kelvinhead.  By now the intermittent rain and drizzle had in the main relented, just long enough for me to get my walking boots off and after a quick repositioning of my gear around the back seat of John’s car, we were away on our trip heading farther north in to the beautiful wilds of northern Scotland. 

  

Survey Result:

Yr Wyddfa

Summit Height:  1084.8m (converted to OSGM15) (Ordnance Survey historical data to bedrock at summit) 

Summit Grid Reference:  SH 60985 54374 (Old triangulation pillar and Ordnance Survey historical data to bedrock at summit) 

Bwlch Height:  47.6m (converted to OSGM15, Trimble GeoXH 6000)

Bwlch Grid Reference:  NS 75797 78295 (Trimble GeoXH 6000)

Drop:  1037.2m (Ordnance Survey historical data to bedrock at summit and Trimble GeoXH 6000 bwlch)

Dominance:  95.61% (Ordnance Survey historical data to bedrock at summit and Trimble GeoXH 6000 bwlch)

 

 

My thanks to Alan Dawson with help processing these data

 

For details on the 1^st summit survey of this hill

 

For details on the 2^nd summit survey of this hill

 

For further details please consult the Trimble Survey Spreadsheet 

Mapping Mountains – Trimble Surveys – Yr Wyddfa

13.05.25  Castell (SH 625 512) 

Castell (SH 625 512) 

A day in the company of Mark Trengove and John Kirk investigating Cwm Llan with a small prominence hill thrown in to keep the surveyor happy.  Cwm Llan is impressive and almost alpine like as it heads skyward from the confines of Nant Gwynant.  This cwm eventually butts up against the southern face of Yr Wyddfa, which is mainly hidden on the lower section of the Watkin Path due to the bulk of Yr Lliwedd as its south-western façade tumbles down toward the upper cwm.

The continuing high pressure system gave idyllic conditions, with a welcome slight breeze, beautiful blue sky and warmth predominating.  We had a number of objectives during our planned walk and were at the car park and starting our ascent of the Watkin Path by 11.20am. 

The south face of Yr Wyddfa

The car park is positioned at approximately 80m in height and therefore the Watkin Path gives the greatest ascent of any of the six major walking routes leading to the summit of Wales’ highest peak.  In its lower part are a series of waterfalls and these today were gathering the masses with a number of bikini clad young ladies venturing up the path.

We had no intention of aiming for the delights of the summit of Yr Wyddfa, but planned on reaching the upper quarry and examine the rocks hereabouts as well as on our route up. 

The start of the Watkin Path

The Watkin Path was built under the guidance of Sir Edward Watkin, who in the late 1800s had purchased the southern side of Yr Wyddfa and built the Chalet; his residence in North Wales.  Watkin was a remarkable person and the Wikipedia page dedicated to his life is a much better place to read of his exploits rather than any I could attempt to write.

Unfortunately the Chalet burnt down in 1960, but we wanted to find its remains and also examine the rocks close by.  Our interest in the rocks en route was partly based on having two enthusiastic geologists in our midst, the third person being the surveyor and blogger. 

The greens of early summer

The initial route up the path was beautiful in late morning dappled light casting through the greened trees, giving both intimacy and welcome shade.  John had pinpointed where the remains of Watkin’s Chalet were and they are easily found, being straight beside the path just before it joins another path heading up from the lane that leads to the farm of Hafod y Llan. 

The flat grassed area that was once the front garden of Walkin's Chalet

We investigated the remains for quite sometime, finding the stone walled corner of the building as well as the old stove, which was now upturned on top of one of the two small piles of discarded remains, now forgotten amongst a plethora of bricks and debris.

It was here that Gladstone stayed when he visited Sir Edward and officially opened the path to the summit.  The plaque commemorating the event is pinned to what is known as the Gladtone Rock and was one of a number of things we wanted to visit during our exploration; however this exploration mainly consisted of taking fragments of rock for later analysis, all of which were labelled and bagged. 

The old stove, now upended

We stopped for lunch under an outcrop of rock just above the remains of Watkin’s old residence.  It was shaded here and relatively quiet with just a few people heading down from the hill and a few also heading up.  We waved and asked where they were heading to and from; many that were heading up were aiming for the stream and waterfalls having seen them on TikTok.

After lunch we continued up out of the shaded confines of the lower wooded area and now in to the direct sunlight, which remained with us for the majority of the day ahead, only disappearing due to the relative lateness of our descent. 

The continuation of the path leading to the waterfalls

We broke off from the main path before the waterfalls and headed toward a small prominence hill beside the steep disused incline that wedged its way through the bwlch of the hill.  This incline would at one time have been used in conjunction with one of a number of working quarries that dot the upper cwm.

The recorded name of the hill is Castell and it looked attractive from our approach, with steep sides of rock and grass and newly sprouted fern and bluebells as accompaniment.  As I headed up, John settled in the shade of the flat bedded incline at the bwlch, whilst Mark followed me. 

The view of Yr Wyddfa and the waterfalls from Castell

The top of the hill had a couple of candidates for high point, each relatively close to one another.  I chose my spot for high point and proceeded to assemble the Trimble to gaher summit data.  As it quietly beeped away gathering its individual datum points I stood a safe distance away so as not to disturb satellite reception, scribbled all necessary detail in my surveying notebook and admired the view down to Nant Gwynant and up toward the summit of Yr Wyddfa.  It really was a marvelous place to be on such a beautiful day, and one that can only have an occasional visit from a rogue hill walker or two. 

Gathering data at the summit of Castell

Once the Trimble had done its stuff I hesitantly made my way down through the stepped rock and joined John and Mark in the shade for late lunch and conversation.  We still had a bit of ascent to do until reaching the top quarry and therefore after packing everything away we headed back to the main path and up past the series of waterfalls and bathers. 

The path above the waterfalls

On our way to the upper quarry we visited the Gladstone Rock.  This is where William Ewart Gladstone, who at the time was aged 83 and serving his fourth term as Prime Minister, spoke to the gathered masses of Eryri and for want of a better phrase declared the Watkin Path open. 

The plaque commemorating Gladstone's visit

I was looking forward to another shaded rest when we reached the memorial plaque, but all too soon we were off upward, following the path as it headed beyond the upper waterfalls to the quarry masters old residence and the upper quarries beyond the great spur of Craig Ddu, which plummets downward from the south-western façade of Y Lliwedd. 

The quarry master's old residence

It was here we rested, but not for long as Mark had his eye on a large rock around the upper cwm that had no doubt deposited itself from the ridge of Allt Maenderyn above, so as he headed off John and I sat in shade, chatted and relaxed. 

Heading toward the upper quarry

Mark was gone for 30 minutes or so, we watched him make progress toward his boulder and then heard the distinct sound of hammer on rock as another sample was bagged and labelled.  As he started his descent back toward us John headed up to an intermediary high point waiting his return. 

Yr Aran

All that remained was the descent to the valley below.  An easy thing to write, but by now the toil in the sun had taken its toll and on the lower section I suffered as sweat continued to bubble from my brow and my steps were getting shorter in length as my willpower ebbed.  However, I’ve encountered many such descents and all one has to do is put one step in front of the other and eventually the car is reached. 

The south face of Yr Wyddfa

Having arrived at the car I changed quickly in to dry clothes and we headed down valley to the delights of a welcome meal in the Prince Llewelyn pub.  After the meal Mark drove back to Mold and I eventually arrived home just before midnight.  It had been a long but very rewarding day.

 

Survey Result:

 

Castell                                        

Summit Height:  157.2m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 62554 51296 (Trimble GeoXH 6000)

Bwlch Height:  147.2m (LIDAR)

Bwlch Grid Reference:  SH 62525 51293 (LIDAR)

Drop:  10.0m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  6.36% (Trimble GeoXH 6000 summit and LIDAR bwlch)

                                       

 

For further details please consult the Trimble Survey Spreadsheet 

Mapping Mountains – Trimble Surveys – Crib Goch

 

05.10.24  Crib Goch (SH 624 551), Pt. 914.6m (SH 623 551), Pt. 901.8m (SH 622 551), Pt. 906.2m (SH 619 551), Pt. 563.0m (SH 638 551) and Carreg Gwalch (SH 642 552) 

The early birds had already gathered at Pen y Pàs, but pure thriftiness, or perhaps self-imposed meanness, had destined my course past them for a lower starting point near the bottom of Bwlch Llanberis.  As I wearily stumbled out of the car, I spotted lights up on the darkened skyline as an even earlier bird traversed along the north ridge of Crib Goch.  This mountain was the primary surveying objective for the day. 

Sunrise.  Photo: Aled Williams

A steep ascent was tempered by scenes of sunrise, with the silhouette of a cloud-capped Moel Siabod beautifully framed by the walls of Y Pàs, its narrow road conspicuously snaking up the valley below.  Periodic rests allowed me to appreciate the ruggedness of these mountains, vast slopes riddled with rock features of various character.  I marvelled at these being the workplaces of the shepherds, the true “mountain men”. 

Base of the north ridge.  Photo: Aled Williams

I had now arrived at the base of the north ridge.  A fair-weather day had been promised but with 30mph wind speeds and these were most definitely present with occasional blusterier spells.  As I ventured onto the start of the arete, I took note of the greasy rocks, not yet dried from the dampening effects of the overnight mists.

The lower arete.  Photo: Aled Williams

Before continuing further I decided to prepare myself for surveying, in case the winds made it difficult to retrieve the various pieces of equipment whilst on the ridge.  The downside of this was that the collection of objects hanging around my neck and stuffed into pockets restricted movement and tended towards imbalance!  I would have to take the traverse carefully and slowly. 

The upper arete.  Photo: Aled Williams

Despite a few uncomfortable blasts from the wind, the ascent of the north ridge went by without incident and I soon found myself at the eastern end of the summit arete, where a few flocks of those early birds were resting having ascended via the east ridge.  I decided that it would be best to go on before them, thus giving me the opportunity to set up the Trimble GeoXH 6000 while they traversed past me, meaning that data collection could then occur without interference from passers-by. 

The summit arete.  Photo: Aled Williams

My memory of the highest point was thankfully incorrect and it proved a relatively sheltered and safe position to spend what would otherwise be a disproportionate amount of time on such an airy summit.  I immediately started to collect 5 minutes of data once the first group of people passed by and was not interrupted by others.  I packed away the equipment happy with the thought that the summit of Crib Goch had now been surveyed. 

Surveying the summit of Crib Goch.  Photo: Aled Williams

The next objective was to survey the bwlch and then the summit of the highest of Crib Goch’s famous pinnacles.  Both points were easily surveyed, with an Abney level being used to locate the highest spike of rock atop the pinnacle. 

A window on the world.  Photo: Aled Williams

As I packed away the equipment atop the highest pinnacle, numerous groups were now making their way along the summit arete.  It was getting busier and this would make surveying the lowest of the pinnacles very difficult. 

The highest of the pinnacles.  Photo: Aled Williams

The problem became apparent once I arrived at the bwlch of the lowest pinnacle.  Its position was a nick between two rocks, exactly at the start of the easiest route that allows passage up and over the pinnacle.  The best approach was to survey it in a time window between the groups of people.  Unfortunately, the tight confines of the bwlch impacted the Trimble’s ability to reach its required accuracy level for measurement.  Just as it was close to reaching this level, a group of people would pass and it would shoot back up to inaccurate levels again! 

The problematic tight bwlch of the lower pinnacle.  Photo: Aled Williams

After a frustrating 45 minutes at the bwlch, data was eventually collected.  I quickly scrambled to the top of the lowest pinnacle and located the highest spike of rock through use of an Abney level.  In contrast, this survey went smoothly and within 10 minutes it had been completed. 

Surveying the summit of the lowest pinnacle.  Photo: Aled Williams

I descended to Bwlch Coch and headed straight to the bwlch of the next top to be surveyed (Pt. 906.2m at SH 619 551).  This was formerly listed as a Welsh Highlands Sub, but was deleted in March 2023 following LIDAR analysis that gave the top only 9.8m of drop.  Given the highly marginal nature of the LIDAR result, this was a priority survey to complete. 

The bwlch of Pt. 906.2m.  Photo: Aled Williams

As the Trimble gathered data, I sat on the grassy edge looking down to Cwmglas Mawr.  The vista of lakes and peaks beyond was stunning, as was the one behind me of Clogwyn y Garnedd and Lliwedd.  A short walk along the narrow ridge of the top brought me to the summit rocks and the Trimble was duly positioned for 5 minutes of measurement. 

Surveying the summit of Pt. 906.2m.  Photo: Aled Williams

After packing up the equipment I headed back to Bwlch Coch, taking the unpleasantly steep descent to Llwybr Pyg during the height of the midday heat.  My final objectives of the day were two Welsh Highland Subs found on the ridge between Bwlch y Moch and Pen y Pàs: Pt. 563.3m and Carreg Gwalch.  These surveys were completed efficiently with not a single walker met along the entire length of the pleasant undulating ridge that joins the two tops together.  All that remained of an excellent day’s surveying was the long plod back to the car.

Pt. 563.0m and Carreg Gwalch.  Photo: Aled Williams.

Survey Result: 

 

Crib Goch

Summit Height:  924.0m (converted to OSGM15, Trimble GeoXH 6000) (average of three surveys)

Summit Grid Reference:  SH 62418 55182 (Trimble GeoXH 6000)

Bwlch Height:  857.2m (LIDAR)

Bwlch Grid Reference:  SH 62168 55116 (LIDAR)

Drop:  66.8m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  7.23% (Trimble GeoXH 6000 summit and LIDAR bwlch)  

 

 

Pt. 914.6m

Summit Height:  914.6m (converted to OSGM15)

Summit Grid Reference:  SH 62309 55153

Bwlch Height:  904.1m (converted to OSGM15)

Bwlch Grid Reference:  SH 62336 55149

Drop:  10.6m

Dominance:  1.16%

 

 

Pt. 901.8m

Summit Height:  901.8m (converted to OSGM15)

Summit Grid Reference:  SH 62258 55130

Bwlch Height:  892.5m (converted to OSGM15, Trimble GeoXH 6000)

Bwlch Grid Reference:  SH 62268 55133 (LIDAR)

Drop:  9.3m

Dominance:  1.03%

 

 

Pt. 906.2m

Summit Height:  906.2m (converted to OSGM15)

Summit Grid Reference:  SH 61983 55146

Bwlch Height:  896.1m (converted to OSGM15)

Bwlch Grid Reference:  SH 61885 55154

Drop:  10.1m (Welsh Highland Sub Reinstatement)

Dominance:  1.11%

 

 

Pt. 563.0m

Summit Height:  563.0m (converted to OSGM15)

Summit Grid Reference:  SH 63821 55162

Bwlch Height:  552.8m (converted to OSGM15)

Bwlch Grid Reference:  SH 63750 55175

Drop:  10.2m (Welsh Highland Sub addition)

Dominance:  1.82%

 

 

Carreg Gwalch

Summit Height:  546.0m (converted to OSGM15)

Summit Grid Reference:  SH 64238 55249

Bwlch Height:  531.2m (converted to OSGM15)

Bwlch Grid Reference:  SH 64229 55166

Drop:  14.7m (Welsh Highland Sub addition)  

Dominance:  2.70%

 

 

For further details please consult the Trimble Survey Spreadsheet