Mapping Mountains – Trimble Surveys – Arenig Fach

 

02.04.21  Pt. 522.7m (SH 744 433), Pt. 516.0m (SH 742 433), Y Garnedd (SH 741 431) and Carreg y Foel Gron (SH 744 427) 

Carreg y Foel Gron (SH 744 427)

Between the lockdowns imposed last year, Aled and I surveyed a number of hills around and including Graig Goch (SH 751 447).  This hill is impressive with its westerly facing crags always a delight to view.  The day proved wonderful with clear blue skies, albeit chilled for much of the day. 

To the south of Graig Goch lies Y Garnedd, these two hills can be easily combined but surveying necessitates an inordinate amount of time spent concentrating on one patch of land, therefore when visiting Graig Goch it was this hill that we concentrated our efforts on and the survey of Y Garnedd would have to wait for another day.  That materialised today and conditions were remarkably similar to our outing on Graig Goch; with clear blue skies but with a chilled easterly breeze. 

I met Aled in the parking area beside Llyn Dubach and we soon had the second car parked at the end of the fisherman’s track, which enabled us to also survey the connecting bwlch between Y Garnedd and Graig Goch. 

The route to this bwlch is simple but can be rather boggy.  We found the critical point of the bwlch positioned beside a stone wall below an imposing lump of rock.  As the Trimble gathered its allotted data we caught up with all manner of things, mainly hill related, but as ever it was good to chat.  Email contact or zoom meetings for those inclined, was a means to keep in contact during the various Covid lockdowns, but nothing betters face to face contact. 

Heading toward the bwlch of Y Garnedd

Between this bwlch and the summit of Y Garnedd are two lower prominence hills that we wanted to survey.  I’d surveyed each with my basic levelling staff in September 2004, now we had the opportunity to produce far better data and determine an accurate drop value for each. 

Pt. 522.7m (SH 744 433)

The first of these hills is given a 522m summit spot height on the Magic Maps website and its high point was easy to identify and consists of rock.  As the Trimble quietly beeped away I scribbled all necessary details in my notebook and after the allotted data were gathered and stored, I closed the equipment down and joined Aled as we sauntered the short distance down to its connecting bwlch. 

Gathering data at the summit of Pt. 522.7m

Gathering data at the bwlch of Pt. 522.7m

Prior to our visit Aled had assessed the details for these hills using 5m contouring and produced interpolated ten figure grid references for each bwlch position, these proved a good indicator for where these critical points lay and once there we then assessed the lay of land by eye.  The critical bwlch for this first hill was positioned amongst moor grass close to an unsavoury pool of stagnant water, which I plunged a boot in to when trying to step across it. 

Pt. 516.0m (SH 742 433) 

It was only a short distance to the second of these two lower prominence hills and we found its connecting bwlch to be positioned on an attractive flat rocky rib, and within a few minutes the Trimble was set up gathering data. 

Gathering data at the bwlch of Pt. 516.0m

Gathering data at the summit of Pt. 516.0m

The summit of this second hill has a wonderful viewpoint with the crags of Graig Goch and the dappled blue waters of Llynnau Gamallt on grand display, whilst the bulk of Y Garnedd rose to our south with its westerly facing cliff looking impressive. 

Y Garnedd

Whilst summit data were gathered I sat with Aled and enjoyed a couple of sandwiches, it was good to be here.  The hills are wonderful places, they can be investigated on solo expeditions or in company, they give individual as well as shared experience and today these hills were an ideal place to catch up after many months of lockdown and enjoy their surroundings. 

Heading up Y Garnedd

Once the Trimble was packed away I followed Aled up the steep grassed and broken ground beside the edge of the westerly cliff of Y Garnedd, stopping occasionally to look back toward Graig Goch.  What a place to be, with the higher Eryri peaks dominating the extended view and unadulterated blue sky stretching in all directions. 

Graig Goch and Llynnau Gamallt

Graig Goch

The high point of Y Garnedd is beside the lower of two cairns and once the Trimble was set up gathering data I joined Aled in the near wind shelter and waited for data to be stored.  During this we heard the rumbling of a vehicle; it sounded similar to a quad bike but once the allotted data were gathered and stored and the Trimble closed down, a 4x4 vehicle suddenly emerged making its way toward us.  This was a surprise to say the least; I’d rarely seen such a vehicle so high on a Welsh hill before. 

Gathering data at the summit of Y Garnedd

I scampered the few metres to say hi to the driver and he pulled up straight next to the summit.  We spent about ten minutes chatting with Tom Ashman and his friend, they’d come from Penmachno and Tom said that he’d driven to this summit a few times before.  I took a number of photos as the vehicle looked so unusual parked beside the summit. 

An unexpected visitor

We left Tom and his friend at the top of the hill and followed the vehicle track down toward the access track that makes its way to the disused Foel Gron Quarry; this gave us our onward route to the last summit and survey of the walk. 

Carreg y Foel Gron is an unusual hill as its connecting bwlch with Y Garnedd is relatively flat.  The flat part of this bwlch is due to waste spoil from the old quarry and therefore is not natural.  The natural bwlch is now buried under who knows how many metres of waste spoil.  Dotted across the bwlch are large boulders, a single one being prominent whilst others are grouped together. 

Approaching Carreg y Foel Gron

As the summit of this hill is given a small uppermost 500m ring contour and bwlch contouring between 470m – 480m on contemporary Ordnance Surveys maps it was a candidate for Dewey status many years ago.  Therefore, armed with my old basic levelling staff I surveyed this hill for drop, resulting in a value of 86ft / 26.2m.  This was in June 2000; and in April 2008 John Barnard and Graham Jackson line surveyed this hill, resulting in 26.52m of drop.  These measurements were taken from the flat bedded connecting bwlch and not natural ground at its base; however John and Graham also took measurements from this area and proved that the drop value for the hill cannot exceed 29.4m.  Today we wanted to give the hill an accurate summit height. 

Aled arrived at the summit first and directed me to where the Trimble should be positioned.  It was soon set up gathering its all-important data; during this we sat, rested, chatted and enjoyed the view.  Once the Trimble was packed away we retraced our inward route back to the bwlch and continued down the old quarry track to the paved road and my awaiting car parked beside Llyn Dubach. 

The Trimble set-up position at the summit of Carreg y Foel Gron

I then drove the short distance up the road and then the rutted fisherman’s track to collect Aled’s car.  Leaving Aled to get his walking boots off, I waved my goodbye’s and headed east for another small walk taking in Garth Goch (SH 952 357) and Garth Rhiwaedog (SH 950 349) which are positioned to the east of Y Bala.

 

Survey Result: 

 

Pt. 522.7m

Summit Height:  522.7m (converted to OSGM15)

Summit Grid Reference:  SH 74459 43396 

Bwlch Height:  508.8m (converted to OSGM15)

Bwlch Grid Reference:  SH 74498 43304

Drop:  13.9m

Dominance: 2.66%

 

 

Pt. 516.0m

Summit Height:  516.0m (converted to OSGM15)

Summit Grid Reference:  SH 74296 43367 

Bwlch Height:  504.4m (converted to OSGM15)

Bwlch Grid Reference:  SH 74371 43318

Drop:  11.6m

Dominance: 2.24%

 

 

Y Garnedd

Summit Height:  552.9m (converted to OSGM15)

Summit Grid Reference:  SH 74199 43111 

Bwlch Height:  475.2m (converted to OSGM15)

Bwlch Grid Reference:  SH 74780 43642

Drop:  77.6m

Dominance:  14.04%

 

 

Carreg y Foel Gron

Summit Height:  500.7m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 74464 42764 (Trimble GeoXH 6000) 

Bwlch Height:  471.3m (relative to Trimble GeoXH 6000 summit and line survey drop)

Bwlch Grid Reference:  SH 74595 42835 (hand-held GPS via survey)

Drop:  29.4m (line survey using highest remaining natural ground at bwlch)

Dominance: 5.87% (Trimble GeoXH 6000 summit and line survey drop) 

 

 

For further details please consult the Trimble Survey Spreadsheet

 

Mapping Mountains – Trimble Surveys – Arenig Fach

 

27.09.20  Tomen y Mur (SH 705 386)  

Tomen y Mur (SH 705 386)

When I first discovered hill walking one of the joys was winter time.  The shortened daylight hours gave opportunity to open maps and plan routes for the following year.  When looking through these Ordnance Survey maps I remember first coming across references to a Roman Amphitheatre, Roman Road, Roman Fort and Roman Practice Works.  All of which were placed just to the north of Trawsfynydd.  I was intrigued, but the pull of higher hills dominated my perspective for many years to come. 

All of the above relate to a Roman Fort complex known as Tomen y Mur, and today, along with my brother; Bryn, I visited for the first time.  The visit did not disappoint. 

The Fort complex was built during the governance of Gnaeus Julius Agricola in AD 78, and was abandoned around AD 140.  A thousand years later during the Norman period the site was re-occupied and fortified with a Motte within the walls.  It is this Motte that is now the centrepiece of the complex. 

A number of months ago I’d analysed the summit and bwlch of this hill via LIDAR, partly for any prospective future visit, but also to determine the drop value for the hill.  The LIDAR image for Tomen y Mur appears below. 

LIDAR image of Tomen y Mur

We met on the outskirts of Trawsfynydd and then drove the short distance up a minor road to the small car park that serves visitors to the site.  An information board and large stone with the Parc Cenedlaethol Eryri / Snowdonia National Park emblem with the name Tomen y Mur appearing below are positioned beside the parking area, with the information board giving a suggested walking route through the complex. 

The Snowdonia National Park emblem

We’d picked a good day to visit as early autumnal skies were blue and the air had a slight crispness to it.  A gate gave access to the site and a path led toward an old ruined house at the foot of the Motte, which lends itself to the extended name of Castell Tomen y Mur. 

Heading toward the old ruined farm house and the Motte

The Motte dominates the site and rises similar to an ancient Bronze Age burial mound.  Close to its base are the old ruined farmhouse and a reconstructed part of the walled complex. 

Part of the reconstructed wall

Wandering around Tomen y Mur reminded me of one aspect why I love Wales so, as the site has little fanfare and benefits for it.  Today we had the whole complex to ourselves.  With information, if needed, given by a number of unobtrusive interpretation boards, each positioned beside places of importance. 

Approaching the high point of Tomen y Mur

Being here I wanted to survey the high point of the site which nowadays is the top of the Motte.  Steep on all sides and with the signs of a few routes of ascent we plodded up to where the view opened across to the higher Eryli peaks with the near Moelwynion lined one hill after another, and to our south the expanse of Llyn Traswfynydd glistened in the early morning sunshine. 

Bryn at the summit of Tomen y Mur

It only took a few moments to set the Trimble up and gather its allotted data.  Once data were stored I closed the equipment down and savoured the view. 

Gathering data at the summit of Tomen y Mur

We now headed toward the remains of the bath house on a part of the old Roman road of Sarn Helen.  Close by was where this road bridged a stream tributary and you can still make out where the bridge must once have been. 

Our route back took us to the remains of the amphitheatre which is beside the small parking area, and separated from it by a sturdy Welsh stone wall.  We walked its embankments before heading back to the car.  The visit took a leisurely hour and was one I’d recommend. 

 

Survey Result: 

 

Tomen y Mur  

Summit Height:  303.2m (converted to OSGM15, Trimble GeoXH 6000) (significant height revision)

Summit Grid Reference:  SH 70544 38679 (Trimble GeoXH 6000)

Bwlch Height:  288.1m (LIDAR)

Bwlch Grid Reference:  SH 70674 38754 (LIDAR)

Drop:  15.1m (Trimble GeoXH 6000 summit and LIDAR bwlch) (Welsh Sub-P15 reclassified to Welsh P15)

Dominance:  4.99% (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

 

For further details please consult the Trimble Survey Spreadsheet

 

 

 

 

Mapping Mountains – Trimble Surveys – Arenig Fach

 

20.09.20  Pt. 513.4m (SH 760 439), Graig Goch (SH 751 440), Graig Goch (SH 752 444), Graig Goch (SH 751 447), Graig Goch (SH 750 447), Graig Goch (SH 749 447), Y Clochdy (SH 749 450), Pt. 516.5m (SH 745 449), Pt. 509.0m (SH 745 446) and Pt. 502.6m (SH 743 440) 

Y Clochdy (SH 749 450)

There are few small groupings of hills that are as contrastable when viewed from their east compared to their west than the grouping that takes Graig Goch as their highest.  It is this group that splits the land between the Moelwynion and the Y Migneint that then merges in to the higher Arenig.  From their east it is the moorland of tussock grass, heather and bog that is on show; this is typical Migneint territory and one to be savoured when in its realm.  From the west the crags that give the highest hill its name are on display, with attractive lakes at their base.  Even though the underfoot conditions can still be torturous it is the western aspect of these hills that show them at their best.  This contrast is greatest when approaching the lower southerly part of the Graig Goch ridge from the east.  This is when the crags only manifest when on the ridge and the lakes of Llynnau Gamallt and Llyn Bryn Du spring in to view. 

It was this eastern approach that Aled and I took today.  Meeting at the small parking area beside Llyn Dubach, we soon had our cars re-positioned with one left at the end of the track leading to the fisherman’s path and the other beside Ffynnon Eidda. 

We had a number of surveying objectives for the day which consisted of ten hills; many of these were on the Graig Goch ridge and the majority of the remainder in the land to the west beside the lakes.  Our first hill was literally just above where Aled parked his car and we were soon walking up toward its high point. 

A strong easterly breeze blew as we approached the summit, heralding the onset of autumn.  The summit of this small hill is given a 514m spot height on the Ordnance Survey 1:25,000 Explorer map and its bwlch a 503m spot height.  Both positions were surveyed.  From here pathless moor leads toward the Graig Goch ridge. 

Heading toward the Graig Goch ridge

It was slow going on the moor, picking out two landmarks we wandered toward each before resting for a few minutes and then setting off for the next.  Slowly our first hill of the hill became more distant and we reached the southern end of the ridge.  The contrast couldn’t be greater.  The great sweep of broken crags swept north before swinging north-westward with the two lakes of Llynnau Gamallt stretching below.  I hadn’t been on this hill for 16 years and the memory held from that day matched this as I stood and looked and savoured the view. 

The southern end of the Graig Goch ridge

Llynnau Gamallt

The surveys came thick and fast as we surveyed all summits and connecting bylchau before reaching the high point of the day; the summit of Graig Goch.  This is crowned by a large flattish rock with a neatly constructed cairn on it.  Soon the Trimble was set-up and beeping away collecting its individual data points. 

Gathering data at the summit of Graig Goch (SH 751 447)

Beyond Graig Goch we still had three hills to survey before dropping down to our west and the land beside the lakes.  Two of these are minor prominence tops connected to Graig Goch whilst the third is Y Clochdy; which is a fine hill and especially so when viewed from the west looking east when its bell-like profile is on grand display. 

The cold east breeze of early morning was now slowly being replaced with warming sunshine as the high grey cloud was burnt away, leaving blue skies for the remainder of the day.  Having surveyed the bwlch and summit of Y Clochdy we joined the path leading down toward the wild lands close to Llyn Bryn Du.  Here we left the path and contoured the lower westerly slopes of Y Clochdy to a small notch which proved to be the bwlch of our next hill to survey which overlooks the quiet surrounds of Llyn Bryn Du. 

I’d been surveying around these parts many years ago with my old basic levelling staff but have very little memory of it.  It was good to be back with Aled, who was ever enthusiastic to survey all small tops to add to our ever increasing data for our 500m Welsh list. 

Llyn Bryn Du with Y Clochdy beyond

The next hill was positioned just to the south of Llyn Bryn Du and before its summit we had its bwlch to assess.  This took time as the territory consisted of tussocks, heather and bog, but happy with our chosen position I set the Trimble up and we waited for the allotted data to be gathered and stored.  The summit of this hill consisted of a large rock overlooking Llynnau Gamallt, and proved another fine small hill and one well worth visiting. 

The descent to the lake was past huge rocks with massive clefts splitting their vertical faces.  Edging our way down I made a mental note not to visit this area when misty as there are few navigational aids on the ground and if whatever path exists is not found, the going underfoot would be problematic. 

Thankfully, the afternoon was proving blissful with blue skies above and descending toward the northern edge of the smaller of the Llynnau Gamallt lakes a path contoured around its shore heading toward our next bwlch to survey.  This bwlch connects with a 502m map heighted hill which is listed in the Deweys as Moel Gamallt; this hill is marginal on both height and drop and needed an accurate survey. 

As the Trimble gathered data at the bwlch I sat with Aled on a rock and waited for the allotted data to be stored.  The day had been a long one and this survey was the nineteenth and with one last summit survey afterward it was going to join the ranks of days with 20 or more surveys completed.  There had been one or two of these over the years since I bought the Trimble, but not too many. 

The fisherman's hut beside Llynnau Gamallt

After the bwlch survey was completed I packed the equipment away and we walked the short distance to the fisherman’s hut which is named Shooting Box on the Ordnance Survey map.  This hut is now showing signs of neglect with a few holes in its roof.  We looked inside and found a framed photograph of David Bowie beside mugs, frying pans and an empty milk carton.  There are few places like this amongst the Welsh hills; the ones on the higher hills are mountain refuges and a few others are fisherman’s huts, with the latter usually locked.  This was open and its darkened interior was at contrast to the unadulterated colour and warmth outside. 

Inside the fisherman's hut

Just one summit remained and it was a slow plod to its high point across more tussocks until its grassed summit was reached.  I needed to sit and rest during data collection, relaxing in the sun looking across the larger of the Llynnau Gamallt lakes to the great sweep of crags beyond.  It was a shame to leave, but as ever one must. 

Gathering data at the summit of Pt. 502.6m (SH 743 440)

All that remained was the walk down the hill’s broad easterly flank to connect with the fisherman’s path leading around the southern shore of the larger lake.  From here Y Clochdy and the cliff of Graig Goch dominated the view with its conically shaped profile set against the blue of the lake, a marvellous sight. 

Y Clochdy and Graig Goch from the southern shore of Llynnau Gamallt

It was lovely to reach the car and get my boots off and change before driving on the rutted track to the minor road and heading the short distance north to Aled’s car.  The walk had taken 8 hours 20 minutes, and although not great in length we accomplished all surveying objectives with 20 surveys taken and some special little hills visited.  A stunningly beautiful area!

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. 

 

Survey Result: 

 

Pt. 513.4m  

Summit Height:  513.4m (converted to OSGM15)

Summit Grid Reference:  SH 76032 43918

Bwlch Height:  503.2m (converted to OSGM15)

Bwlch Grid Reference:  SH 76084 44174

Drop:  10.2m

Dominance:  1.99%

 

 

Graig Goch  

Summit Height:  548.2m (converted to OSGM15)

Summit Grid Reference:  SH 75134 44061

Bwlch Height:  539.2m (converted to OSGM15)

Bwlch Grid Reference:  SH 75141 44092

Drop:  9.0m

Dominance:  1.64%

 

 

Graig Goch  

Summit Height:  576.3m (converted to OSGM15)

Summit Grid Reference:  SH 75223 44423

Bwlch Height:  564.4m (converted to OSGM15)

Bwlch Grid Reference:  SH 75201 44487

Drop:  11.9m

Dominance:  2.07%

 

 

Graig Goch  

Summit Height:  589.5m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 75124 44714 (Trimble GeoXH 6000)

Bwlch Height:  466.3m (LIDAR)

Bwlch Grid Reference:  SH 73958 45093 (LIDAR)

Drop:  123.1m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  20.89% (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

 

Graig Goch  

Summit Height:  587.2m (converted to OSGM15)

Summit Grid Reference:  SH 75092 44781

Bwlch Height:  577.8m (converted to OSGM15)

Bwlch Grid Reference:  SH 75131 44759

Drop:  9.4m

Dominance:  1.60%

 

 

Graig Goch  

Summit Height:  585.1m (converted to OSGM15)

Summit Grid Reference:  SH 74997 44799

Bwlch Height:  577.9m (converted to OSGM15)

Bwlch Grid Reference:  SH 75073 44794

Drop:  7.1m

Dominance:  1.22%

 

 

Y Clochdy  

Summit Height:  577.6m (converted to OSGM15)

Summit Grid Reference:  SH 74972 45046

Bwlch Height:  559.4m (converted to OSGM15)

Bwlch Grid Reference:  SH 75075 45001

Drop:  18.1m

Dominance:  3.14%

 

 

Pt. 516.5m  

Summit Height:  516.5m (converted to OSGM15)

Summit Grid Reference:  SH 74568 44934

Bwlch Height:  506.0m (converted to OSGM15)

Bwlch Grid Reference:  SH 74620 44956

Drop:  10.5m

Dominance:  2.03%

 

 

Pt. 509.0m  

Summit Height:  509.0m (converted to OSGM15)

Summit Grid Reference:  SH 74586 44601

Bwlch Height:  499.7m (converted to OSGM15)

Bwlch Grid Reference:  SH 74643 44752

Drop:  9.3m

Dominance:  1.84%

 

 

Pt. 502.6m  

Summit Height:  502.6m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 74376 44064 (Trimble GeoXH 6000)

Bwlch Height:  471.4m (LIDAR)

Bwlch Grid Reference:  SH 74446 44361 (LIDAR)

Drop:  31.2m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  6.21% (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

 

For further details please consult the Trimble Survey Spreadsheet