Mapping Mountains – Trimble Surveys – Mynydd Hiraethog

18.09.19  Pen yr Orsedd (SH 892 555), only bwlch surveyed

Pen yr Orsedd is a fine unassuming hill with its high point consisting of a few rogue embedded rocks amongst its grassland moored summit.  The last time I visited was in June 2014 with Mark Trengove and Aled Williams.  As the Trimble gathered its customary summit data we lazed in the sun with Llyn Alwen forming a majestic backdrop.

Gathering data at the summit of Pen yr Orsedd (SH 892 555)

Since the summit survey the 5m contouring on the OS Maps website has become available and this is proving an excellent resource when checking on height values and their placement, and in the main, is proving more accurate compared to the standard contouring on Ordnance Survey 1:25,000 Explorer maps. 

The summit height produced by the Trimble GeoXH 6000 for Pen yr Orsedd is 442.211m and with an estimated bwlch height of c 409m based on contouring between 400m – 410m it meant that this hill was relatively safe as a Pedwar with an estimated c 33m of drop.  However, the 5m bwlch contours on the OS Maps website is between 410m – 415m with interpolation giving an estimated bwlch height of c 412m, with this value giving the hill an estimated c 30m of drop, which is the minimum drop value for Pedwar status.  Therefore the bwlch needed to be surveyed and given an accurate height.

The bwlch of Pen yr Orsedd is positioned close to the A543 road as it makes its way north-eastward from the outskirts of Pentrefoelas toward Dinbych (Denbigh).  Google maps indicated I could park at the entrance to a small disused quarry a couple of hundred metres from where a gate gives access down to the area of the bwlch.  Having parked I walked the short distance to the gate where there is now a long flat gravelled area beside the road with sufficient space for a number of cars to be parked.

The bwlch looked relatively inviting with beige tinged moor grass predominating, interspersed with occasional rogue tussocks.  Leading from the gate was a sheep path and a line of vehicle tracks on the moored grass.

The bwlch of Pen yr Orsedd

I was soon at the area of the bwlch and the sheep path crossed directly over it, although contour interpolation placed its critical point slightly to the north.  Having deposited my rucksack on where I judged the bwlch to be positioned, I walked a short distance up the opposing hillside to look down on it from a different viewpoint.  I then contoured to the south and decided that my rucksack was placed at its critical point.

Sauntering back to the bwlch I aligned the placement of the Trimble atop my rucksack with the critical point of the bwlch and set it to gather data.  During data gathering I again ventured up the opposing hillside and decided that I should take a second data set from just south of the equipment’s current position.

Gathering data at the bwlch of Pen yr Orsedd

Whilst the Trimble quietly beeped away gathering its individual datum points I took a series of photos with a succulent yellowed moor as foreground and the great mass of sun drenched Yr Wyddfa floating above all surrounds as backdrop.

Yr Wyddfa floating above the moor

Once the allotted data were gathered and stored I headed a short distance southward and positioned the Trimble again atop my rucksack to give it elevation above its immediate surrounds.  This time it was placed directly on top of one of many impressive rounded green grassed tussocks beside the start of a bogged water course that indicated this placement to be lower than the first, which agreed with my visual inspection.

The set-up position for the second data set at the area of the bwlch of Pen yr Orsedd

Bwlch surveying was proving very enjoyable.  It is much easier than summit surveying and especially so if positioned beside a road.  This bwlch proved another wonderful place with just the occasional sheep as company, the bwlch just sat there, seldom visited and giving tranquillity to an otherwise busied scene with the main road being so close. 

Once the allotted data were gathered from the impressive greened grassed tussock I packed the Trimble away and walked the short distance back to my car, checked the map and headed further north-east to the next bwlch, which connects to the Pedwar of Bryn Trillyn.

Survey Result:

Pen yr Orsedd

Summit Height:  442.2m (converted to OSGM15, from previous Trimble GeoXH 6000 survey)

Summit Grid Reference:  SH 89294 55542 (from previous Trimble GeoXH 6000 survey)

Bwlch Height:  409.2m (converted to OSGM15)

Bwlch Grid Reference:  SH 90076 55064

Drop:  33.0m

Dominance:  7.47%

For details on the summit survey of Pen yr Orsedd

  

For further details please consult the Trimble Survey Spreadsheet

Mapping Mountains – Trimble Surveys – Mynydd Hiraethog

29.06.14  Llys Dymper (SH 894 591), Pen yr Orsedd (SH 892 555), Moel Rhiwlug (SH 885 552), Pen Bryn Ci (SH 872 563) and Moel Seisiog (SH 860 573)

Moel Seisiog (SH 860 573)

Mynydd Hiraethog is an expanse of moor land on the edge of Eryri with its western confines looking out towards the highest peaks in Wales.  Forty square miles of its central land is now covered in the Clocaenog Forest which was planted in 1905; this coniferous forest has Llyn Brenig and the Alwen Reservoir on its western fringe with Llyn Aled and Llyn Alwen just to its north-west.  The area is sometimes referred to as the Denbigh Moors and is crossed by the A543 as it heads north-east from its junction with the A5 near Pentrefoelas to the town of Dinbych (Denbigh).  Outside of the conifer plantation the land gives a feeling of openness, one that is seldom visited except by farmer and the occasional hill walker.

Today’s walk was proposed by Aled as a horseshoe from the hamlet of Gwytherin (SH 876 615), heading clockwise around a number of Pedwar hills, with alternatives for a descent route dependent upon time and energy.

We met at Mark’s house on the outskirts of Yr Wyddgrug (Mold) and headed in one car to Gwytherin.  Parking can be found on the road in the hamlet next to the Lion Inn, a pub we hoped to visit after the walk for drinkies and eaties, unfortunately it doesn’t cook on a Sunday and its door was locked when we did visit.  However, it does look good and probably well worth a visit.

Our route to the hills headed southward out of Gwytherin on a narrow dead end lane that soon turned in to a track beyond the farm of Bryn-y-clochydd (SH 878 608).  This track proved an easy way to gain height toward our first hill; Llys Dymper.  The forecast for the day was ideal with a slight northern wind giving clarity of colour as the showers of yesterday and the lingering cloud on the higher Eryri peaks was replaced with big blue sky and pleasant warmth.

Aled and Mark on the track heading toward Llys Dymper

The high point of Llys Dymper has a number of rocks on it and what looks like the remains of part of an old plough, as Aled made conversation with a farm worker who was seeing to the gathered sheep, I set the Trimble on the high point of the hill for five minutes of data collection. 

The summit of Llys Dymper (SH 894 591)

As we set off toward the marginal Sub-Pedwar of Moel Llyn (SH 899 573) the view west was a constant backdrop, a line of mountains from the Rhinogydd, Moelwynion, Yr Wyddfa, Glyderau and Carneddau, all grey profiles etched in sun and shadow.  This view remained with us for much of the day, never disappointing.

(L-R)  Yr Aran, Moel Siabod, Yr Wyddfa and Crib y Ddysgl

(L-R) Yr Wyddfa, Crib y Ddysgl, Glyder Fawr, Glyder Fach and Tryfan

The high Eryri peaks from the western Hiraethog

On our way toward Moel Llyn we flagged a Landrover down as it drove toward us; the driver was the local farmer who Aled then spent a half hour with.  The farmer was more than welcome to impart his knowledge of the hills which Aled noted on his map.  Many names and anecdotes were given, some of the names matched those on contemporary Ordnance Survey maps, others did not, whilst some names on current maps were no longer in use and had been supplemented by others.  Aled will write all of this up and do further research in to the names the farmer gave him.

Aled with map in hand making place-name enquiries with the local farmer

Beyond Moel Llyn we dropped down to Ty’n-llyn, a now deserted farmhouse next to the waters of Llyn Alwen.  Access to this house is only by track, it has an outbuilding that was once a boathouse, its position both a lonely but stunningly desolate place to make a life’s living.  Today we sat in the sunshine, listened to fish jumping in the lake and appreciated the surroundings.

Heading toward the quiet waters of Llyn Alwen

Where sky, moor and water meet

The remains of Ty'n-llyn beside Llyn Alwen

The access track to Ty’n-llyn took us toward our next summit of the day; Pen yr Orsedd, before heading east over the moor to its summit we watched three off-road vehicles pass us slowing edging their way on the track toward the ruined house.

As the Trimble gathered five minutes of summit data from Pen yr Orsedd we sat in the sunshine and chatted.  The high point of the hill proved to be an embedded rock with moss growing on it, a good hill with the blue waters of Llyn Alwen as backdrop.

Gathering data at the summit of Pen yr Orsedd (SH 892 555)

The next hill; Moel Rhiwlug is listed as a Sub-Pedwar with 29m of drop, it was this hill that we were most interested in for data collection, as with one more metre of drop it would enter the ranks of Y Pedwarau.  It has two options for its critical bwlch, one to the west and one to the east of its summit.  The western bwlch option is probably higher and therefore where the critical bwlch is positioned, the eastern option has two possibilities for its bwlch position.  As we re-joined the track from the summit of Pen yr Orsedd I quickly surveyed each eastern bwlch option with a spirit level and placed the Trimble on the high point of the valley to valley traverse on the lower of the two.  During this Mark and Aled lounged in the sun patiently waiting for the Trimble to do its stuff.  Next stop was the summit of Moel Rhiwlug, again another five minutes of data were gathered from the high point.

Moel Rhiwlug (SH 885 552) a Sub-Pedwar with 29m of drop

Gathering data at the summit of Moel Rhiwlug

As I packed the Trimble away and Mark collected his ten figure grid reference for the summit on his hand-help GPS, Aled headed off toward the western bwlch, this looked rather expansive from the summit.  Slowly Aled got further and further away becoming no more than a silhouetted figure in an expanse of open moor as the higher Eryri peaks looked on.

Aled disappearing in to the expanse of moor as he heads toward the bwlch of Moel Rhiwlug

Soon Mark and I headed down to join Aled, Mark had input the coordinates of the ten figure bwlch spot height that appears on the Ordnance Survey enlarged Geograph map.  The whole area proved a flatland of tussock and heather outcrop where the thought of accurate line surveying would be a novel experience.  By the time we met Aled, he had stomped around on the flatland and had decided upon the position where he thought the critical bwlch lay, Mark had followed the spot height grid coordinates and was standing no more than 15 metres from where Aled was, quite remarkable considering how expansive and wild the area of the bwlch is.  I positioned the Trimble on its improvised Tupperware and draughts board tripod so it had some elevation above the morass of undergrowth.  The measurement offset between ground level and the position of the Trimble’s internal antenna will be taken off the processed result.  Once the required data had been gathered it was packed away and we headed toward the hill we have listed as Pen Bryn Ci.

The Trimble GeoXH 6000 on its improvised Tupperware and draughts board tripod

Relaxing in the sun waiting for the Trimble to gather its allotted bwlch data

As we headed toward the summit of Pen Bryn Ci we came across three horses with two small foal’s running on the hillside, a welcome addition to such an open landscape.  The underfoot conditions on the way to this summit proved mainly pathless but an occasional stop for munching on bilberry’s seemed to help progress.  The summit has a cairn on top fashioned to resemble a small wall, as the Trimble gathered its data we sat in the sun and admired the view.  Just one summit remained, the highest of the day; Moel Seisiog.

Heading toward the summit of Pen Bryn Ci

Looking back at Moel Rhiwlug from the lower slopes of Pen Bryn Ci

Relaxing at the summit of Pen Bryn Ci (SH 872 563)

The land between the summit of Pen Bryn Ci and Moel Seisiog was surprisingly easy to walk, especially so beyond the connecting bwlch, where a vehicle track on the moor helped progress up to a gate which gave access to the summit trig point.  By now the sun had moved toward the western sky and the earlier detail edged on the high Eryri peaks had been replaced by a gentle smoothness as blue and grey merged to outline their growing bulk.  The Trimble was placed on the highest ground I could find adjacent to the trig pillar and gathered another five minutes of data.

The summit trig point atop Moel Seisiog (SH 860 573)

Our downward route was north-eastward across the moor toward the old farmhouse of Ddol-frwynog (SH 872 579).  From here we picked up a track at the head of the valley that became the paved road, all around was the luxuriance of high summer with vivid greens of grass and hedgerow with overhead deep blues of sky, sounds of distant farm dog’s and the gentleness of a moving stream, and all passed through in an instant, never to be replaced.  The paved road continued for quite some time leading us forever nearer to our starting point at Gwytherin, where we found the pub shut – Boo Hoo!

Part of the outbuilding adjoined to the old farm house of  Ddol-frwynog

The track at the head of the valley that leads down to the hamlet of Gwytherin

On the way down the road we came upon this house sign; almost but not quite!

Postscript:

Since surveying 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, and where appropriate LIDAR has been used in preference to that produced by the Trimble.

LIDAR image of Moel Rhiwlug (SH 885 552)

Survey Result:

Llys Dymper

Summit Height:  466.2m (converted to OSGM15, Trimble GeoXH 6000) 

Summit Grid Reference:  SH 89467 59177 (Trimble GeoXH 6000) 

Bwlch Height:  396.45m (LIDAR)

Bwlch Grid Reference:  SH 89377 56945 & SH 89383 56940 (LIDAR)

Drop:  69.8m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  14.96% (Trimble GeoXH 6000 summit and LIDAR bwlch)

Pen yr Orsedd

Summit Height:  442.2m (converted to OSGM15)

Summit Grid Reference:  SH 89294 55542

Bwlch Height:  409.2m (converted to OSGM15, from subsequent Trimble GeoXH 6000 survey)

Bwlch Grid Reference:  SH 90076 55064 (from subsequent Trimble GeoXH 6000 survey)

Drop:  33.0m

Dominance:  7.47%

Moel Rhiwlug

Summit Height:  433.5m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 88525 55275 (Trimble GeoXH 6000)

Bwlch Height:  404.6m (LIDAR)

Bwlch Grid Reference:  SH 88058 55301 & SH 88063 55302 & SH 88061 55303 (LIDAR)

Drop:  28.9m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  6.67% (Trimble GeoXH 6000 summit and LIDAR bwlch)

Pen Bryn Ci

Summit Height:  447.4m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 87220 56352 (Trimble GeoXH 6000)

Bwlch Height:  400.6m (LIDAR)

Bwlch Grid Reference:  SH 88883 55346 (LIDAR)

Drop:  46.8m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  10.46% (Trimble GeoXH 6000 summit and LIDAR bwlch)

Moel Seisiog

Summit Height:  467.2m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 86093 57306 (Trimble GeoXH 6000)

Bwlch Height:  398.8m (LIDAR)

Bwlch Grid Reference:  SH 87063 56679 (LIDAR)

Drop:  68.4m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  14.64% (Trimble GeoXH 6000 summit and LIDAR bwlch)

For details on the bwlch survey of Pen yr Orsedd

For further details please consult the Trimble survey spreadsheet click {here}