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 – Garn Fawr

17.06.25  Carn Llidi (SM 737 280) 

Carn Llidi (SM 737 280)

Carn Llidi is rock strewn in its higher reaches and protected from any off-path ascent by copious amounts of tough undergrowth.  The hill is positioned north-west of Tyddewi (St David’s) which purports to be the smallest city in the British Isles.  It looks out over a jagged coastline which the Pembrokeshire Coast Path follows.  Although the hills hereabouts are good, it is the coastal path that is the highlight. 

Pentre Ifan

We were based at Caerfai for a few days, which is just to the south and easy walking distance from Tyddewi.  On our way to Caerfai we visited Pentre Ifan, which is one of Wales’ most impressive ancient burial sites with its upper monolith delicately balanced. 

Inside the chapel at St Non's

The coastal path was next to where we stayed; we walked to Solfach (Solva) and bussed it back to the city and on another day headed to the delights of St Non’s; a Catholic retreat beside the coast path. 

The cathedral at Tyddewi

Whilst at Tyddewi the first Welsh Bible was transferred to the cathedral.  It was translated by Bishop William Morgan and published in 1588.  It had never been on public display and along with the first Bible published in Irish was now at the cathedral.  Whilst visiting to see this Bible I stood and listened to four elderly ladies talking amongst themselves in Welsh, whilst pointing at the book housed in its display cabinet.  I found this scene rather emotional as this book played a crucial role in preserving the Welsh language and over 430 years later this small group of neatly dressed women were a testament to the importance of this book and the strength of the language. 

The first Welsh Bible

As well as hills, coastal walks and the cathedral, the land surrounding Twddewi also looks west to a series of islands dominated by Ynys Dewi (Ramsey), which I had visited and surveyed its three P30 hills in May 2016.  However, there are many more islands scattered beyond Ynys Dewi with the main grouping being Emsger, Carreg Rhoson and North Bishop.  And when at Caerfai we took two boat trips; the first around Ynys Dewi and the second a magical evening trip to North Bishop. 

On the coastal path

However stunningly beautiful the coastal path and islands are, and however interesting and historically significant the cathedral is, we also needed a hill to visit.  The one that looked the most impressive was Carn Llidi.  I contemplated bringing the Trimble to survey its summit, but the prospect of carrying the equipment for six days with only one hill to visit was not appealing and therefore the Trimble remained at home and LIDAR would have to suffice for the numerical details of this hill. 

The highest of the chain of islands known as North Bishop

We parked on a grass verge on the B4583 road at it descends to its end at Whitesands beach.  This gave opportunity for a circular walk with only the uphill section back on the narrow paved road at the end of the walk as a repeat. 

Beside the narrow road leading down to Whitesands

Setting off the weather was again lovely; with crisp blue sky heralding what we hoped would be another glorious day.  However, weather hereabouts was proving fickle.  Each evening I watched from the elevation of Caerfai as thin cloud banks quickly rolled landward and then quickly dissipated as the sun cast out again, only for another cloud bank to follow.

Our route took us down to the beach, where we were confronted by a multitude of school children, all donned out in wet suits with their paddle boards aimed at the sea.  It was good to walk on the beach, somewhere we would revisit for an afternoon during a particularly warm spell of weather later in the week.  Our walk this time on its sands was only short as we headed north and soon joined the coastal path. 

Suzanne on the coastal path leading north from Whitesands

This section was like others we had visited with dramatic plummeting views downward to rocky coves, sandy beaches and towering sea stacks, and all experienced with the sea a constant blue and today the sky casting radiant.  It was indeed a good day to be out, but that weather hereabouts is a fickle beast. 

The view back toward Whitesands

We were looking for a path on our right leaving the main coastal path and which, hopefully, would take us toward our hill.  Thankfully we found it as the prospect of walking through the tough undergrowth away from any path is not recommended.

The path swung up gaining ground and always heading toward the western end of the Carn Llidi summit ridge.  As with many similar hills leaving the path can course calamitous results of floundering in copious amounts of evil undergrowth.  Therefore, I thought it prudent to ask one or two fellow walkers who were heading down in the opposite direction, whether and where the path continued.  We were met with conflicting advice, some encouraged going back down to another path and others seemed to discourage anything to do with venturing high on the hill.  I found this advice rather unusual, thanked them and off we went forever upward. 

Murky conditions starting to set in over Ynys Dewi

The path eventually swung up on to a concreted section leading to the summit of Carn Llidi Bychan; an outlier of the main peak and the farthest extension of the rocky western end of the summit ridge.  As height was gained we looked out toward Ynys Dewi, which was now being overtaken by one of those fickle weather conditions with grey murk approaching.

Ancient burial chamber beside the path on the way to Carn Llidi

The initial continuation toward the main peak was easy enough, with a variety of narrow paths leading toward the upthrust of the summit cone.  As we reached where path butted against rock, Suzanne decided that was far enough for her and found a sheltered spot away from the increasing strength of the wind, to wait until I visited the summit and hopefully descended safely back to where she was now happily sitting and admiring the view northward. 

Approaching the summit cone of Carn Llidi

When approaching Carn Llidi from the west its highest point requires hands on rock to reach its summit.  I used to hunt out any scramble and have many fond memories of weekends spent in Nant Peris, evenings in the Vaynol Arms, breakfasts in Pete’s Eats and late mornings and afternoons venturing on to Eryri peaks via scrambling on rocky ridges.  This at that point of my life was the norm.  I found it highly enjoyable and considered myself competent enough to know when to back off from something that looked beyond my limit.  However, age and scrambling not being the norm can quickly lead to lack of confidence on rock, and this was only confounded when in October 2023 I slipped and fell from a rocky ridge close to Moel Hebog.  Falling on the opposite side of the ridge would probably have resulted in death.  I was fortunate to walk away with just a large bruise on my upper thigh and a few scratches.  This experience dampened any confidence I had left when confronted with hands on rock and those scrambles that in my younger days were the norm.  Today was the first time I had encountered rock since the day I had fallen.  This all sounds rather melodramatic, but it is as it is and it feels good to write about such things and be as honest as I can.

Before venturing up the rock I took my rucksack off and left it at the base of the summit cone and safely zipped my camera in its case.  The way up was obvious as the rock was discoloured through many peoples visits over the years, it involved two sections of scrambling before reaching the high point, the first up a diagonal wide groove and the second a metre or two traverse to the left and then up a few steps to where the summit opened up.  By the time I reached the top it was definitely windy, not so much to be dangerous but enough that I was thankful I had decided not to bring the Trimble.

The view north-eastward up the coast from the summit of Carn Llidi

Reversing my upward route was relatively easy, as with most things of a similar nature, taking ones time is essential.  Soon I was back at my rucksack and shortly afterward sitting beside Suzanne tucking in to some yummy morsel of food.  As we gathered our stuff to head down we felt the first drop of rain that was being pushed landward beyond the grey sky murk that we had seen over Ynys Dewi on the latter part of our ascent.

Our route down was easy, reversing the summit ridge to Carn Llidi Bychan and the narrow concrete path leading down to the main path, here we continued down toward the road, instead of swinging rightward and rejoining the coastal path.  This soon brought us out on to the road and that nasty little bit of uphill at the end of the walk, never the best at the end of any walk. 

Relaxing in the car with our picnic with the cloud base now enveloping Carn Llidi

During our descent the weather continued to close in, with those succulent blue skies of earlier now replaced by greying murk with intermittent spells of light coastal drizzle being brought in on the wind.  The rain was never heavy enough for me to put waterproofs on and we arrived back at the car still dry from our endeavours.  All that remained was a quick change whilst the kettle was boiling and to have a feast of a picnic sitting in comfort looking out of the car window as the whole upper ridge of Carn Llidi disappeared under grey murk. 

 

Survey Result: 

 

Carn Llidi 

Summit Height:  182.1m (LIDAR)  

Summit Grid Reference:  SM 73797 28001 (LIDAR)

Bwlch Height:  57.8m (LIDAR)

Bwlch Grid Reference:  SM 76096 28625 & SM 76132 28642 (LIDAR) 

Drop:  124.3m (LIDAR)

Dominance:  68.27% (LIDAR)

 

 

For further details please consult the Trimble Survey Spreadsheet 

Mapping Mountains – Trimble Surveys – Carnedd Wen

 

13.07.23  Yr Allt (SJ 242 100, previously Trimbled) 

Yr Allt (SJ 242 100)

It was my pleasure today to join Sarah Kerr on part of her Offa’s Dyke walk.  Sarah had contacted me a few weeks ago and asked if I would like to join her for a few hours as she was walking part of the long distance footpath north of Welshpool.

Considering how wet recent days have been we were ever so fortunate with the weather as although an occasional slow moving shower was forecast for parts of Wales, any grey cloud that materialised did not develop in to rain and our walk remained dry. 

Sarah Kerr

I met Sarah at 8.30am on the Rhallt Lane outside the recently built and large property where she overnighted.  The morning was beautiful with blue sky and the hint of warmth in the air.  It was good to see her as the last time our paths crossed were a number of years ago when trips to Welsh islands and lighthouses were organised.

Prior to meeting I suggested the possibility of including an ascent of Yr Allt from the Rhallt Lane and dropping off the hill back on to the canal towpath which hereabouts also forms a part of Offa’s Dyke footpath.  Sarah was on for this, therefore after pleasantries we walked up the steep lane chatting about all manner of things.  The conversation must have been good as even though I’d been this way a number of times over recent years we overshot the footpath I planned for us to follow.  This meant we remained on the lane as it turned in to a track and we followed it to its high point. 

In the field leading toward the trig pillar

At the end of the track a footpath continues through undergrowth to connect with a forest track, however we now headed to our right on to a steepening field where wild flowers predominated, with a plethora of butterflies flitting this way and that in the warmth of the strengthening sun. 

Approaching the trig pillar

This part of the field forms a ridge that leads ever upward to where the triangulation pillar sits confidently looking north-eastward out toward the Breiddin and the higher hills to the west.  The western horizon was dominated by the Y Berwyn ridge with the higher Aran also on show, with their elongated ridge still battling with wisps of cloud which no doubt would soon be burnt off. 

The distant Y Berwyn

Leaving the trig pillar we lost height heading toward the corner of the lower field, where a stile gives access to another field leading past the large mast that can be seen from many miles away signifying the summit area of this hill.  Shortly beyond is the high point, it doesn’t afford the view that the ground beside the trig pillar does, but it is the summit and therefore with my bagging hat on it had to be visited. 

Sarah at the summit of Yr Allt

To get on to our descent route we now doubled back to the trig pillar and followed the ridge downward past pheasant pens and the Gamekeepers Cottage at the end of the forest track.  Down we went heading toward the Coppice Cottage where many a year ago I used to live.  However, before the cottage is a forest track on the right that heads down through the wood.  I had always wanted to investigate this track and see where it leads.  Having already mentioned this to Sarah she had no objection to us investigating this route.

The track led us down through the wood and seemed to grind to a halt where summer undergrowth of nettles and brambles then took over.  Just below us was a high pheasant fence which conveniently for us had been flattened due to a tree bow falling on it.  However, between us and it was all manner of debris which entailed an assault course to get through, which we eventually did, emerging on to an open field and with the aid of mapping on Sarah’s mobile phone we were soon directed down the field to a footbridge crossing the canal.

After crossing the footbridge we had one barb wired fence to negotiate before reclaiming the canal towpath.  Our onward routes now headed in opposite directions, Sarah farther northward following the footpath of Offa’s Dyke and southward for me back toward Welshpool. 

Sarah heading off on the canal towpath to continue her Offa's Dyke journey 

Before heading our separate ways we had a hug and I thanked Sarah for the invite to join her.  It had been an immensely enjoyable few hours with good company, good conversation and a hill thrown in for good measure!

Survey Result: 

 

Yr Allt

Summit Height:  231.3m (converted to OSGM15, from previous Trimble GeoXH 6000 survey)

Summit Grid Reference:  SJ 24240 10005 (from previous Trimble GeoXH 6000 survey)

Bwlch Height:  125.9m (LIDAR)

Bwlch Grid Reference:  SJ 21855 08773 (LIDAR)

Drop:  105.4m (Trimble GeoXH 6000 summit and LIDAR bwlch) 

Dominance:  45.57% (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

 

For details on the first Trimble GeoXH 6000 summit survey of Yr Allt

For details on the second Trimble GeoXH 6000 summit survey of Yr Allt

For details on the Trimble GeoXH 6000 bwlch survey of Yr Allt

For details on a third visit to the summit of Yr Allt

For details on a fourth visit to the summit of Yr Allt

For details on a fifth visit to the summit of Yr Allt

 

 

For further details please consult the Trimble Survey Spreadsheet

 

 

Mapping Mountains – Trimble Surveys – Yr Eifl

 

17.09.22  Mynydd Mawr (SH 140 258) 

Mynydd Mawr (SH 140 258) from a previous visit to the hill

As a child my family holidayed at Morfa Nefyn and Edern.  I have a distant memory that during one of these holidays we headed to the end of Pen Llŷn and drove up the concrete road that leads to the summit of Mynydd Mawr.  We could have done this more than once, but my memory only retains small segments from my childhood and even these only give me the semblance of one distant childhood visit. 

For many years we spent our holidays in this house in Morfa Nefyn

It would be many years later when I next visited this hill and since then I have been back to survey its summit and visited again with my brother.  This time I was with my aunt, cousin and brother.  We were staying in Nantlle and a road trip taking in the beauty of the Llŷn had been suggested. 

The view from the coast at Nefyn

It is all too easy to accept the land one lives in; after all it is the land one is used to.  However, heading from Welshpool to Nantlle my aunt and cousin both marvelled at the beauty of the land we were travelling through.  I had done this journey countless times over many years and although I would like to think my eye is still appreciative of this land, there is no doubt an acceptance on my part, as for me it is a constant.  Seeing it with new eyes through the experience of my aunt and cousin gave me added appreciation of just how beautiful this land is and by that fact, how fortunate I am to live where I do.

On our way down Pen Llŷn we visited the old houses where we holidayed, reminiscing on times now long gone.  A multitude of narrowing lanes lead west down the Llŷn toward the paved road that starts its way up Mynydd Mawr, this soon turns in to a concrete road ending at the top of the hill, where a levelled section gives adequate parking for a number of cars.  We weren’t the only ones heading up this hill, there were a few walkers on the manicured green paths, but in the main it was the convenience of a car that brought people here. 

Looking inland toward the high Eryri peaks

Having parked I sauntered off to stand on the high point and before joining Bryn, Shirley and Julie I took a few minutes to look inland toward the higher peaks of Eryri which were framed by a sweeping coastline.  It was a stunning view, whilst behind the great swathe of the Irish Sea dominated, following this around and the bulk of Ynys Enlli looked back as a darkened silhouette, whilst to its right a slight greyed outline of the distant Wicklow hills, south of Dublin could just be picked out.

Leaving the summit I joined Bryn, Shirl and Julie on the series of steps leading down with the distant Ynys Enlli ahead.  We followed these for a while before stopping, all round was the expanse of sea, a huge blue mass stretching to the horizon. 

Looking out toward Ynys Enlli

We stayed looking out to sea for quite some time and once heading back up the steps we veered rightward to join one of the paths leading up the hill toward the top, this soon led us back to the car.  It’s always good to visit this summit, be it by foot or car.  It signifies an end of land and if the weather conditions are favourable, as they were today, it can give a dramatic element to this beautiful land that we live in. 

 

Survey Result:

 

Mynydd Mawr

Summit Height:  160.0m (converted to OSGM15, from previous Trimble GeoXH 6000 survey)

Summit Grid Reference:  SH 14021 25869 (from previous Trimble GeoXH 6000 survey)

Bwlch Height:  64m (spot height)

Bwlch Grid Reference:  SH 14952 26292 (spot height)

Drop:  96m (Trimble GeoXH 6000 summit and spot height bwlch)

Dominance:  60.00% (Trimble GeoXH 6000 summit and spot height bwlch)

 

 

For details on the survey of Mynydd Mawr

For details on the 2^nd visit to Mynydd Mawr

 

For further details please consult the Trimble Survey Spreadsheet