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 Laird 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