Mapping Mountains – Trimble Surveys – Moel Hebog

 

10.04.21  Graig Goch (SH 496 485), Graig Goch (SH 495 484), Graig Goch (SH 497 485), Mynydd Graig Goch (SH 497 485), Graig Goch (SH 498 483), Garnedd Goch (SH 511 495) and Pt. 733.4m (SH 525 502) 

Garnedd Goch (SH 511 495)

Since getting the Trimble there are few places that I’ve wanted to survey more than the hills that comprise the Nantlle ridge.  In the past these hills dominated many of my weekends as my mother lived in Nantlle.  When visiting I would open the skylight at night in the converted attic bedroom, let my eyes become accustomed to the dark and then follow the ridge line from the upper part of Garnedd Goch to the ground above Craig Cwm Silyn.  On moonlit nights these hills sparkled with their crags plummeting to the darkened moorland and grazing fields below. 

The Nantlle ridge is one of the walking highlights of Wales.  It beckons with many a subline hill profile.  Many years ago I took every opportunity to visit, the majority of which were two car linear walks; either with a friend to accompany me doing the ridge or with someone to drop me off at one end of it.  These were the days before Mynydd Graig Goch was declared a 2,000ft mountain, this ‘news’ still entertains many of the locals. 

When the survey result of Mynydd Graig Goch hit the headlines I proceeded to visit its high point each month until my monthly round total matched the other 2,000ft Welsh hills, this entailed 16 ascents.  I’d set off usually from the parking area close to the high mast that dominates the skyline to the north-west of the hill.  Occasionally I investigated the paths leading up the hill via its bwlch connecting it with Garnedd Goch. The hill never disappoints; its summit tors are marvellous to either walk or scramble up.  The hill is also the last 2,000fter in Wales before the Llŷn heads westward.  Mynydd Graig Goch is a fine hill and I hadn’t visited it for 12 years.  Neglecting such a hill can also enthuse to re-visit and when this hill and its many tors were suggested for a surveying expedition I was easily tempted. 

The person doing the tempting was Aled who wanted one particular tor surveyed.  Mark joined us for the day and by around 10.30am we were parked and walking up the track leading toward Llyn Cwm Dulyn.  As both Aled and Mark are quicker than me, I set off before them slowly gaining height on the path that heads up from the track leading to the lake.  This was the same path that we used when originally surveying Mynydd Graig Goch in 2009.  Then the weather deteriorated and proved positively vile on the summit, where we hunkered down for over two hours as James Whitworth’s Leica equipment gathered the all-important summit data. 

Garnedd Goch rising above Llyn Cwm Dulyn

Today the forecast gave mainly dry conditions with the prospect of wintery showers in the afternoon brought on by a chilled northerly breeze.  As I made steady progress up the well-defined path I occasionally glanced backward and although other people were using the same path there was no sign of Aled or Mark. 

By the time I neared the upper rocky part of the hill I had two pairs of gloves, an ear warmer and fleece balaclava on as the northerly breeze was wind-like.  However, the ridge was clear as indeed were all near hills.  It was a sheer joy to be back on this hill, its tors brought back so many memories, the people with me and the reasoning for repeating visits, all add to the varied texture of memory, the company shared and the weather conditions encountered, even that chilled two hour wait for data to be gathered when I ended up shivering and soaked through, this still brings a smile to my face when I think of it. 

The first tor I reached was the one I thought Aled wanted surveying.  Its high point consisted of a flake of rock.  I positioned the Trimble with its internal antenna aligned with the high point and then wedged it in place with a number of rocks.  By the time five minutes of data were gathered and stored I was joined by Aled, who looked at me and asked why I was surveying this tor, when I replied that I thought this was the one he wanted surveying, he laughed and pointed down to our south-west where a lower but more prominent tor was positioned.  I laughed back at him, but as the summit of this first tor had been surveyed we decided to do likewise for all the other major tors on the hill. 

Gathering data at the first rock tor - Graig Goch (SH 496 485)

As the Trimble was packed away Mark emerged with a broad grin on his face and was soon standing in celebratory fashion beside the flag pole that now adorns this tor.  The second rock tor we surveyed is impressive, we collected data from its connecting bwlch and summit during which Aled and Mark hunkered down out of the chilled northerly wind and I stood an appropriate distance away from the equipment so as not to get in the way of satellite reception and waited for the allotted data to be gathered and stored. 

Gathering data at the second rock tor - Graig Goch (SH 495 484)

Between the second tor and the high point of Mynydd Graig Goch is another tor of similar, but importantly slightly lower height.  This was surveyed with the Leica Smartrover in 2009 and also proved to break through the magical 609.6m / 2,000ft benchmark height.  The same tor was now surveyed with the Trimble GeoXH 6000. 

Gathering data at the third rock tor - Graig Goch (SH 497 485)

The next tor on our continuing surveying agenda was the pinnacle of rock that constitutes the summit of Mynydd Graig Goch.  To my knowledge this is the first time this point has been surveyed since the Leica equipment was strapped to its side.  Then just over two hours of data were gathered, today it was six minutes. 

The Leica SmartRover gathering data at the summit of Mynydd Graig Goch

During data collection I stood below the equipment looking out toward Garnedd Goch as it rose skyward with its impressively built wall framing its south-westerly flank.  Shadows danced across near hills, whilst others sank in shade with their profiles rearing skyward.  This part of Wales as with many others is always special as valley and hill meet in usually dramatic fashion. 

Gathering data at the fourth rock tor - Mynydd Graig Goch (SH 497 485)

Garnedd Goch with the snow-capped Yr Wyddfa and Y Lliwedd in the background

Once the Trimble was closed down we had one last remaining tor to visit and survey, this had its bwlch and summit Trimbled before we headed down to the path across the moor that heads for the connecting bwlch between Mynydd Graig Goch and Garnedd Goch. 

Gathering data at the fifth rock tor - Graig Goch (SH 498 483)

Reaching the bwlch we said our goodbye’s to Mark as he wanted to visit the Pedwar of Ffridd Arw Uchaf and that would entail repositioning his car.  This left Aled and I to survey the bwlch of Mynydd Graig Goch which proved one of the easiest to identify as it was tight on both the hill to hill and the valley to valley traverse.  Once the allotted data were gathered and stored I followed Aled on the same path that Mark was now descending, toward the connecting wall that heads up to the summit of Garnedd Goch. 

Heading toward the bwlch of Mynydd Graig Goch

Gathering data at the bwlch of Mynydd Graig Goch

I rested a few times heading up beside the wall but made steady progress.  Eventually the remains of the weather battered trig pillar came in to view as did the large ancient cairn that now incorporates the summit of this hill.  When I joined Aled at the summit we debated where data should be gathered.  There were two large rocks below the trig pillar, but as other smaller rocks were higher and these seemed solid enough we decided that as they had been there an inordinate amount of time they could be deemed as being a part of this hill’s summit. 

Gathering data at the summit of Garnedd Goch

From the summit of Garnedd Goch the view opens to the high Eryri peaks with Yr Wyddfa still snow-capped and looking forever inviting with its great ridges curving around its higher domain.  It always entices from this view and more so from the highest point of the Nantlle ridge which was now ahead of us. 

Yr Wydfa from Garnedd Goch

Between us and this high point was the connecting bwlch of Garnedd Goch and we were soon there assessing where its critical point lay.  Its whereabouts was not too difficult to pinpoint and soon the Trimble was set up quietly beeping away gathering its all-important data. 

Gathering data at the bwlch of Garnedd Goch

Just the last major uphill of the day remained; toward the high point of the Nantlle ridge.  This is given as Craig Cwm Silyn in many hill lists, however this name is strictly applicable to its northerly cliff face and not to the hill itself, as this is known locally by a different name which, for now, is being kept back, so the hill is being listed by the point notation. 

Approaching the high point of the Nantlle ridge

The summit of this hill is positioned in its wind shelter where two small embedded rocks vie for its high point.  Having chosen our preferred highest I set the Trimble up on top of my rucksack to give it elevation above its immediate surrounds, measured the offset between its internal antenna and the ground at its base and waited for the 0.1m accuracy level to be attained before data should be logged.  Once this figure appeared on the screen I pressed ‘Log’ and joined Aled sitting on a part of the tumbled rock making up the wind shelter as the allotted data were gathered and stored. 

Gathering data at the summit of Pt. 733.4m (SH 525 502)

This summit affords one of the best views anywhere in Wales with Yr Wyddfa as backdrop and the slender grassed ridge leading from Mynydd Tal y Mignedd to Trum y Ddysgl as foreground, with the latter seemingly suspended in motion.  Similar to a painted picture hung and admired, this view never disappoints. 

One of the best views in Wales

All that remained was to devise a route off the hill and I left Aled to do that.  I happily followed as we looked down the steep crags of a part of Craig Cwm Silyn as our path slithered across its top.  Beyond this we encountered rough ground, leaving the path to cross the wall that makes its way up Garnedd Goch from its north-west.  The rough ground continued beyond with tough moor grass and hidden rocks and it did not make for a quick descent although it felt as if we sped across it. 

Heading down

Down we went and eventually connected with the path that leads upward to the bwlch where Mark had left us.  This now gave favourable underfoot conditions giving relatively easy going and led us to the outflow of Llyn Cwm Dulyn where a footbridge joined with our mornings inward track.  The last hour or so had given beautiful colour with the hills starting to glow in early evening light.  It was a fitting end to a magical day on the hill. 

 

Postscript 

Since visiting these hills full LIDAR coverage is now available.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height and positional data that is now freely available for England and Wales.  Consequently the numerical details for these hills have been analysed using this technique, resulting in the LIDAR height and position being used for some of these hills.

 

Survey Result: 

 

Graig Goch

Summit Height:  607.4m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 49645 48570 (Trimble GeoXH 6000) 

Bwlch Height:  c 603m (interpolation)

Bwlch Grid Reference:  SH 49671 48586 (interpolation)

Drop:  c 4m (Trimble GeoXH 6000 summit and interpolated bwlch)

Dominance:  0.72% (Trimble GeoXH 6000 summit and interpolated bwlch)

 

 

Graig Goch

Summit Height:  597.9m (converted to OSGM15)

Summit Grid Reference:  SH 49522 48444   

Bwlch Height:  585.9m (converted to OSGM15)

Bwlch Grid Reference:  SH 49541 48497

Drop:  12.0m

Dominance: 2.01%

 

 

Graig Goch

Summit Height:  609.6m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 49707 48555 (Trimble GeoXH 6000) 

Bwlch Height:  606.3m (LIDAR)

Bwlch Grid Reference:  SH 49717 48534 (LIDAR)

Drop:  3.3m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  0.54% (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

 

Mynydd Graig Goch

Summit Height:  609.8m (converted to OSGM15, Trimble GeoXH 6000) 609.8m (converted to OSGM15, Leica SmartRover 1200)

Summit Grid Reference:  SH 49729 48515 (Trimble GeoXH 6000) SH 49729 48515 (Leica SmartRover 1200)    

Bwlch Height:  535.9m (converted to OSGM15)

Bwlch Grid Reference:  SH 50929 48808

Drop:  73.8m (Trimble GeoXH 6000) 73.9m (Leica SmartRover 1200 summit and Trimble GeoXH 6000 bwlch)

Dominance: 12.11% (Trimble GeoXH 6000) 12.11% (Leica SmartRover 1200 summit and Trimble GeoXH 6000 bwlch)

 

 

 

Graig Goch

Summit Height:  607.35m (converted to OSGM15)

Summit Grid Reference:  SH 49877 48393   

Bwlch Height:  599.8m (converted to OSGM15)

Bwlch Grid Reference:  SH 49858 48418

Drop:  7.6m

Dominance:  1.24%

 

 

Garnedd Goch

Summit Height:  701.9m (converted to OSGM15)

Summit Grid Reference:  SH 51114 49522   

Bwlch Height:  676.8m (converted to OSGM15)

Bwlch Grid Reference:  SH 51908 49970

Drop:  25.1m

Dominance: 3.58%

 

 

Pt. 733.4m

Summit Height:  733.4m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 52555 50262 (Trimble GeoXH 6000)   

Bwlch Height:  334.9m (LIDAR)

Bwlch Grid Reference:  SH 55308 49663 (LIDAR)

Drop:  398.5m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance: 54.34% (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

 

For further details please consult the Trimble Survey Spreadsheet