Mapping Mountains – Trimble Surveys – Hirddywel

 

07.05.21  Domen Ddu (SO 016 782), Pt. 540.0m (SO 019 787), Crugyn Llwyd (SO 024 796), Pegwn Mawr (SO 023 812) and Pegwn Bach (SO 017 805) 

Crugyn Llwyd (SO 024 796)

Having asked permission to park my car at the entrance to Grach farm I was walking along the continuation of the narrow lane that heads south by just past 8.00am.  My plan for the day was to visit and survey the hills on the southerly part of the main Pegwn Mawr ridge.  I’d visited Domen Ddu and Crugyn Fawr on two previous occasions, but along with these hills I wanted to survey Pegwn Bach; as its name implies a lower and adjacent hill connected to Pegwn Mawr. 

There was a slight chill in the air as I set off, with low light accentuating the rippled shadows moving across the land, pushed along by a wakening breeze.  The forecast gave generally dry conditions with an outside chance of an early afternoon shower materialising. 

Early morning heading toward the southerly part of the main Pegwn Mawr ridge

The main ridge of Pegwn Mawr is now dominated by its wind farm.  I visited this hill before the turbines were installed and remember it being a wild moorland hill.  Now the access tracks lessen this effect, but it is still a good hill to visit, and although I had no definite plan to head as far north as its summit tumulus, it was relatively near Pegwn Bach and especially so as the latter has two potential points for its bwlch and the furthest north of these was literally just below the summit dome of Pegwn Mawr. 

I soon left the narrow lane and continued on a track and again left this after only a short distance to climb a steep closely cropped grass slope upward to a fence.  The grazing fields now relented and moorland took over.  Shortly after crossing the fence I followed a vehicle track contouring upward to the edge of forestry which is situated close to a bwlch that I later surveyed.  But my first objective was the summit of Domen Ddu; a hill that I had surveyed on two previous occasions, the first in September 2002 when assisted by Eryl Selly and Steven Hughes we surveyed the hill for drop using my old basic levelling staff, resulting in 81ft / 24.7m.  The second in June 2008 with John Barnard, Graham Jackson and David Purchase when we line surveyed the hill resulting in 24.3m of drop.  Now I wanted to put an accurate height to its summit and also, if time and inclination was forthcoming, its bwlch, as it is always good to compare data produced by the Trimble GeoXH 6000 against other surveying methods. 

By the time I neared the summit tumulus on Domen Ddu cloud had built up, therefore the land was cast in patches of direct sunlight and shade and when the sun enhanced the colour I took every opportunity to take photographs and approaching the summit tumulus the greens, beiges and rusted fawns of moor grass swept toward the upper part of the hill.  At times like this, when on my own and the beauty of upland landscape is fleetingly enhanced by direct sunlight, it still has the power to stop me in my tracks and just look and take in the scene. 

Approaching the summit tumulus atop Domen Ddu

I was soon on top of the tumulus and set the Trimble up atop my rucksack with its internal antenna aligned with the highest part of the hill, and once the measurement offset was taken I set it to gather data and stood on the periphery of the tumulus looking north to the other hills I planned to visit. 

The onward route with Pegwn Bach on the left and Crugyn Llwyn central right

Gathering data at the summit of Domen Ddu

Having packed the Trimble away I headed back toward the corner of forestry and then followed reed grass upward to where a bwlch lay.  This bwlch connected to a small prominence hill just to its north.  I took two data sets, each on the valley to valley traverse before heading to its summit.  The high point was relatively easy to identify and consisted of a patch of grass amongst copious amounts of heather and moor grass. 

This summit was an excellent vantage point to look north toward the remaining hills to visit and between it and the summit of my next hill; Crugyn Llwyd was a morass of bleached moor and no doubt bog.  I hoped a semblance of a path existed otherwise it would prove a wet and unrelenting route onward.  Thankfully a vehicle track on the moor contoured around the north-easterly flank and this would at least help me on my way.  Once on it, it led all the way over the connecting bwlch and up toward the summit of Crugyn Llwyd. 

As Domen Ddu had previously been line surveyed I had no definite plan to Trimble its bwlch, but I had noted the ten figure grid reference for it.  However, although the bwlch could have been positioned in a desolate quagmire it was conveniently placed at the track and even without the aid of the ten figure grid reference its position would have been easy to identify.  As I was now there I surveyed it with the Trimble.  As the equipment gathered its allotted data I sat on the edge of the track and watched a Red Kite circle overhead.  As it did so, its head moved leftward looking straight down at me.  I watched it for a number of minutes as it glided the air, circling as it did so; a wonderful sight. 

Gathering data at the bwlch of Domen Ddu

I left the continuation of the track as it was waterlogged from recent heavy rain that had swept the blue skies away over the last few days, and followed a fence line up the southern part of Crugyn Llwyd.  This hill was central on my day’s route and gave good extensive views.  Its high point was easy to identify and after surveying it I continued heading north. 

Pegwn Bach from the summit of Crugyn Llwyd

Gathering data at the summit of Crugyn Llwyd

The continuation of the route from the summit of Crugyn Llwyd was now on moor grass.  I picked up an occasion sheep track on the moor which headed down toward its connecting bwlch and passed over a green track crossing from east to west on my way.  Later in the day I would use this as my descent route back to Grach farm and my car.  But now I had a formidable bwlch to tackle.  It looked horrendous.  It extended across the land in front of me with high tussocks, reed grass and what turned out to be a water laden bog.  I wandered its realm for a number of minutes, balancing from one wobbly tussock to another, always aiming to where I envisaged the valley to valley traverse met with that of the hill to hill traverse.  My chosen spot could easily be 100 – 200 metres out in placement.  However, as I was there I set the Trimble up and gathered the allotted five minutes of data.  During data collection I sat on a tussock which slowly collapsed with the bog progressively making me wetter and wetter. 

Approaching the bwlch of Crugyn Llwyd with Pegwn Mawr in the background

Gathering data at the bwlch of Crugyn Llwyd

Leaving the bog I made my way up toward one of the bylchau that connect with Pegwn Bach.  This small prominence hill has two potential positions for its bwlch.  My initial plan was just to survey one, but I knew that in all likelihood I would survey the two.  I also knew that as the second of these two positions was just below the summit of Pegwn Mawr, I would probably also visit this summit. 

The Trimble was set up beside a small puddle of a pool at the first bwlch and on the moor for the second, and leaving the summit of Pegwn Bach for my return I then continued toward the top of Pegwn Mawr. 

As my hill life is now mainly dictated by surveying I have learned that preparation pays dividends and therefore prior to each walk I analyse available LIDAR and make a note of all relevant grid references.  This takes time, but also saves it when on the hill.  However, I always gain pleasure from unplanned visits and as Pegwn Mawr was not planned for today, I enjoyed heading up to its summit.  This brought back so many memories from my first visit prior to the wind farm being built, to when John, Graham and I surveyed the hill for summit position, to my last visit three years ago with Aled when we surveyed the hill with the Trimble.  As I was now on the summit I set the Trimble up and gathered another summit data set. 

Gathering data at the summit of Pegwn Mawr

Although the equipment was initially placed facing south where the majority of satellites are positioned, after ten minutes of waiting the accuracy level only attained 0.15m, therefore I re-positioned it facing north and within a couple of minutes the 0.1m accuracy level before data should be logged appeared on the screen and I pressed ‘Log’ and stood below it whilst it quietly beeped away gathering data. 

The view north from the summit of Pegwn Mawr

Having said my goodbye’s to the summit of Pegwn Mawr I retraced my inward route back to the first potential bwlch position of Pegwn Bach and continued on a sheep path leading toward its summit.  This is crowned by another ancient tumulus, which is grassed with a prominent cairn positioned on it.  The Trimble was soon set up gathering its eleventh and last data set of the day. 

Gathering data at the summit of Pegwn Bach

It was a relatively easy descent from this hill toward my awaiting car.  One thing I did not want to do was retrace my route back over the connecting bwlch with Crugyn Llwyd.  My eventual route of descent lay on the southern side of a steep stream valley that headed down toward Grach farm.  Leaving the summit of Pegwn Bach I took a direct line toward the summit of Domen Ddu which looked back across the intervening land and then followed a green track of sorts as it headed toward an old rusted gate which gave access to the other side of the stream. 

Nearing Grach farm

Beyond the stream I connected with the descending green track which I had walked over when heading down to the bog laden bwlch of Crugyn Llwyd.  The green track proved a delightful route down, leading me on a steady and comfortable gradient with the early afternoon sun bringing warmth replacing the chilled air from early morning. 

 

Survey Result:

 

Domen Ddu  

Summit Height:  551.8m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SO 01690 78262 (Trimble GeoXH 6000)

Bwlch Height:  527.6m (converted to OSGM15, Trimble GeoXH 6000) (and also relative to 24.262m line survey for drop)

Bwlch Grid Reference:  SO 02166 79025 (Trimble GeoXH 6000)

Drop:  24.3m (line survey)

Dominance:  4.40% (Trimble GeoXH 6000 summit and line survey for drop)

 

 

Pt. 540.0m  

Summit Height:  540.0m (converted to OSGM15)

Summit Grid Reference:  SO 01946 78794

Bwlch Height:  528.0m (converted to OSGM15)

Bwlch Grid Reference:  SO 01979 78656

Drop:  12.0m

Dominance:  2.23%

 

 

Crugyn Llwyd  

Summit Height:  570.0m (converted to OSGM15)

Summit Grid Reference:  SO 02407 79622

Bwlch Height:  531.2m (converted to OSGM15)

Bwlch Grid Reference:  SO 02308 80404

Drop:  38.8m

Dominance:  6.81%

 

 

Pegwn Mawr

Summit Height:  585.3m (converted to OSGM15, average of two Trimble GeoXH 6000 surveys)

Summit Grid Reference:  SO 02391 81239

Bwlch Height:  285.9m (converted to OSGM15, from previous Trimble GeoXH 6000 survey, natural bwlch)

Bwlch Height:  283.8m (converted to OSGM15, from previous Trimble GeoXH 6000 survey, disused rail cutting)

Bwlch Grid Reference:  SN 92693 80074 (from previous Trimble GeoXH 6000 survey, natural bwlch)

Bwlch Grid Reference:  SN 92601 80035 (from previous Trimble GeoXH 6000 survey, disused rail cutting)

Drop:  299.3m (natural bwlch)

Drop:  301.5m (disused rail cutting bwlch)

Dominance:  51.14% (natural bwlch)

Dominance:  51.51% (disused rail cutting bwlch)

 

 

Pegwn Bach  

Summit Height:  567.5m (converted to OSGM15)

Summit Grid Reference:  SO 01766 80573

Bwlch Height:  557.4m (converted to OSGM15)

Bwlch Grid Reference:  SO 01944 80714

Drop:  10.1m

Dominance:  1.78%

 

 

For details on the 1^st summit survey of Pegwn Mawr

For details on the bwlch survey of Pegwn Mawr

For an in-depth examination of the bylchau of Pegwn Mawr and Great Rhos

 

 

For further details please consult the Trimble Survey Spreadsheet