Tuesday, 23 January 2018

Mapping Mountains – Trimble Surveys – Arenig


23.12.17  Graig Wen (SH 739 394, bwlch only at SH 763 403)

The bwlch of Graig Wen

I’m not averse to standing in a bog, they do have unusual pleasures that are mainly ones centred on either remoteness or peacefulness, and solitude is also a quality associated with a good bog. 

Bogs are seldom purposely visited by a hill walker, little detail is needed to explain this as they are usually wet, occasionally impenetrable and sometimes oozing with methane, all of these are seldom sought by a hill walker; usually the summit and the view is priority, but a good bog can also give fulfilment.

Today’s bog looked forlorn when I pulled my car up, it looked particularly wet, mist hugged the adjoining hillsides and a slight drizzle was slowly sweeping up the westerly valley. 

I had little option as far as parking was concerned and pulled by car to the side of the B road that makes its way from Llyn Celyn to Ffestiniog and hoped that it would not obstruct any traffic.

Thankfully during my hour’s immersion in said bog few vehicles passed, and all that did so, easily avoided the seemingly abandoned car pulled up on the side of the road, and for any inquisitive driver catching site of me in the bog I suspect I must have looked an unusual site as I spent the majority of the time waiting patiently for data to be gathered as the Trimble sat on top of my rucksack as I stood a number of metres away scribbling all necessary detail in my notebook whilst taking another photograph of the damp and misty land.

The bog in question is the critical bwlch for Graig Wen (SH 739 394) whose summit was surveyed earlier in the year and whose height came to 555.585m (converted to OSGM15).  This bwlch is given a 417m spot height on Ordnance Survey 1:25,000 Explorer maps, if accurate this would give the hill 138.6m of drop.  However, the bwlch contouring on OS Maps (the recent replacement for OS Get-a-map) is between 410m – 415m, if this contouring is correct it would give Graig Wen over 140m of drop which is sufficient for it to be classified as a Submarilyn.  Not news to excite every hill walker, let alone every hill bagger, but new Submarilyn’s do not appear every day of the week.

As I left my car I donned wellies and quickly made my way down beside reed grass and a vehicle track to the point of the bwlch.  Thankfully the bwlch was only a short distance from the B road and although the majority of time I was immersed in its delights proved misty, my car was always in view.

I spent a few minutes assessing the lay of land and followed a water course westward to where the ground visibly descended, and then retraced my steps to where I had initially thought the critical bwlch to lie.  It was here that I took the first of what proved to be four data sets.  The second being where I had walked to, both positions were wet and beside the oozingly green water course.

Gathering the first data set

Gathering the second data set

Wellies were proving essential as I squelched around the bwlch for the next 50 minutes or so, this way and that, balancing from one wet tuft of moorland grass to another.

The third data set was taken from where the 417m spot height is positioned on the ground, visibly this was higher than the position of the first two data sets, but the ground also seemed to ever so slightly rise and then dip again, and it was the water course that led me to thinking where my preferred critical bwlch position to be.

Gathering the third data set

I had a prior appointment with Aled in Porthmadog at 11.00am, so quickly set the Trimble up for the fourth data set on the eastern side of the fence that crosses the area of the bwlch and positioned it beside the continuation of the water course and where the land visually then descended.

Gathering the fourth and last data set

Once the fourth data set was stored and happy with my hour’s activity I abandoned the delights of the bog and walked back up to my car and the onward journey to Porthmadog.      



Survey Result:


Graig Wen

Bwlch Height:  414.6m (converted to OSGM15)  

Bwlch Grid Reference:  SH 76301 40330

Drop:  141.0m (prospective Submarilyn addition)

Dominance:  25.38%






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