Mapping Mountains – Trimble Surveys – Bryniau Dyfi

20.10.16  Cribin Fawr (SH 794 152), Waun Oer (SH 785 147) only bwlch surveyed), Craig Portas (SH 801 141), Mynydd Gartheiniog (SH 807 142), Mynydd yr Hewyrch (SH 816 150) and Maen Du (SH 822 151)

Cribin Fawr (SH 794 152)

Bwlch Oerddrws is one of the gateways between the east and its gentle sloping hills and the ruggedness of the west at it plunges toward the coast, and at over 360m it is also a convenient starting point to tackle the Aran ridge to its north or part of Bryniau Dyfi to its south.  It was the latter Alan and I visited today, this was the second day out with the Leica and Trimble and I was enthusiastic to see how my right knee dealt with the rigours of two consecutive days in the hills after I twisted it a number of weeks ago.

By the time we parked the Dyfi hills were clear of cloud and the forecast for the remainder of the day was good with only an occasional shower predicted to meander across the country.

I’d only ascended Cribin Fawr once from this high starting point and then used a zig zagging path that takes an almost direct route onto the hill’s northern ridge, today we decided to explore the path that skirts the hill’s eastern ridge and continues westward to gain the ridge north of the summit.

I set off first and toiled in the overly warm conditions as little breeze was present, but progress was made, as it always is, and as I plodded up the final slopes toward the ridge, Alan appeared in front having taken a path directly up the eastern ridge, and by the time I joined him on the summit of Cribin Fawr he had assembled his Leica RX1250 and it was gathering data.

Alan beside the Leica RX1250 at the summit of Cribin Fawr

When on a part of the Berwyn yesterday we’d used a surveying method with the Leica gathering data for approximately 20 minutes, followed by the Trimble set up over the same point for five minutes, and whilst the latter gathered data Alan headed toward the next survey point to set up his Leica and I would later join him to set up my Trimble, this method worked extremely well and we used it again today.

Gathering data with the Trimble GeoXH 6000 at the summit of Cribin Fawr

Once Leica and then Trimble data were gathered I followed the wet path beside a fence past a number of oozing black peat channels and continued south-eastward down to the first bwlch of the day.  We planned on surveying three main bylchau with each having map contours between 550m – 560m, and therefore their respective hills may swap dependent upon which is higher or lower.

By the time I arrived the Leica was gathering another 21 minute data set, this we listed as the critical bwlch for Waun Oer; a 670m map heighted hill to the south-west of Cribin Fawr.  These meetings at each summit and bwlch gave an opportunity to chat and relax as the equipment gathered its data.

Relaxing at the bwlch of Waun Oer

Gathering data with the Trimble GeoXH 6000 at the critical bwlch of Waun Oer

Looming above us were the steep slopes of Craig Portas which is a 605m map heighted Simm, Dewey and Twmpau, and after Alan had packed the Leica away he headed up as I assembled the Trimble, a few minutes later and with data stored I followed him up to the hill’s featureless summit.  During the first few hours of the walk the sky remained a dulled light grey and the ever present threat of rain pervaded as showers were breaking out further west and north, and occasional spits of rain fell our way on the light breeze that ebbed across the hills, but thankfully no persistent rain or heavy shower materialised during the day on the hills we visited.

Craig Portas (SH 801 141)

The summit of Craig Portas is one that must be usually bi-passed unless visited by a bagger as the main path skirts its upper northern cwm, leaving its summit lonely and tussock ridden, today it was surveyed with both the Leica RX1250 and Trimble GeoXH 6000.  After Alan headed off toward the next bwlch, I remained at the summit and waited for the Trimble to gather its customary five minutes of data and stood looking west toward the higher peaks radiating out from Cadair Idris, whose profile always stands out from the Dyfi ridge.

Alan beside the Leica RX1250 at the summit of Craig Portas

Waun Oer (SH 785 147) from the summit of Craig Portas

I soon joined Alan at the next bwlch, this we listed as the critical one for Craig Portas, the bwlch is a tight affair with a few rogue conifers to its immediate south, and a fence and plunging drop to its immediate north, Alan had set his Leica on an extended pole and after it had gathered 20 minutes of data I placed the Trimble on the top of the Leica antenna and noted a 1.12m measurement offset between its internal antenna and the critical point of the bwlch, and the two of us waited for five minutes of data to be gathered.  As the equipment beeped away gathering its individual data points an occasional flash of sunlight brightened the land giving colour to the otherwise dulled surrounds.

Alan setting the Leica RX1250 up at the critical bwlch of Craig Portas, with Mynydd Gartheiniog in the background

Alan beside the Leica RX1250 at the bwlch of Craig Portas

The Trimble GeoXH 6000 gathering data perched on top of the Leica RX1250 at the bwlch of Craig Portas

The next summit along the ridge is another that must usually be bi-passed unless visited by a bagger as its high point is positioned away from the path which continues toward the high point of these hills; Mynydd yr Hewyrch.  We both visited its top, and as I set the Trimble up Alan continued toward the next bwlch.  This hill is a part of Mynydd Gartheiniog and is listed as such in the 500m Twmpau, whilst Michael uses the name of Craig Portas – East Top in his listing of Deweys.  Its summit consists of soft tussocks with a slight path of sorts leading toward its high point.

Ascending Mynydd Gartheiniog from Craig Portas

Dramatic cloud out to the west

Gathering data at the summit of Mynydd Gartheiniog

As I joined Alan at the next bwlch the western sky started showing signs of late afternoon light as dramatic clouds built up out to the west, this late light remained with us for the remainder of the walk giving beautiful conditions over Cadair Idris and succulent autumnal colours on the high Aran.

As data were gathered at the last of the three main bylchau Alan spotted two people near the summit of Craig Portas, they continued toward Mynydd Gartheiniog and eventually disappeared into the day.  Beyond this bwlch lay a fence line heading toward the summit of Mynydd yr Hewyrch; the high point of Bryniau Dyfi, and as the Trimble gathered the last of its allotted 300 datum points I watched Alan make progress up the slope, beside the fence line and disappearing beyond view.

The Trimble GeoXH 6000 gathering data at the critical bwlch of Mynydd Gartheiniog

Looking toward Cadair Idris from the ascent of Mynydd yr Hewyrch

The summit of Mynydd yr Hewyrch consists of a large watery puddle with four grassed peat hags vying for its high point; it is an unusually attractive place and is one that we spent a great amount of time at, as three points were each surveyed with the Leica and Trimble, with each having been Distoed by Alan.

The Leica RX1250 gathering data at one of the three points surveyed atop Mynydd yr Hewyrch

Late afternoon light above Cadair Idris

The Leica RX1250 gathering data at one of the three points surveyed atop Mynydd yr Hewyrch

The Leica RX1250 gathering data at one of three points surveyed atop Mynydd yr Hewyrch

The Trimble GeoXH 6000 gathering data at one of three points surveyed atop Mynydd yr Hewyrch

The Leica RX1250 gathering data at one of three points surveyed atop Mynydd yr Hewyrch

The Trimble GeoXH 6000 gathering data at one of three points surveyed atop Mynydd yr Hewyrch

As the Leica was set up at the third summit point I headed off toward Maen Du, the 674m map heighted top further east which for many years was the recognised high point of the hill.  As I followed the narrow peaty path colour cascaded down across the hills, it was radiant and piecing in its intensity, giving brilliance to the autumnal colour.  I stopped and soaked in the scene as grey shadowed summits were edged against the glowing greens, oranges and autumnal yellows.

On my way toward Maen Du I stopped and surveyed its connecting bwlch with Mynydd yr Hewyrch and then continued to its summit, where Alan joined me a few minutes later.  The summit of Maen Du was the eleventh survey with the Trimble during the day and once data were gathered and the equipment packed away we followed the path southward around the edge of Craig Maesglase and its impressive plunging waterfall.

Long shadows and autumnal colours at the bwlch of Maen Du

Aran Fawddwy

Gathering data at the summit of Maen Du

By now the colour was intense as the last of the days light illuminated Aran Fawddwy, this late intensity of colour only lasts for a few short minutes as the sun sinks ever lower and once gone it was replaced by a subdued light that crept ever onward toward darkness.

Our route down following the escarpment edge above Craig Maesglase

Aran Fawddwy illuminated in late afternoon light

Succulent autumnal colour illuminating Aran Fawddwy

Maen Du with the high Aran in the background

We arrived back at the awaiting car at 6.55pm in dimmed light, having followed the path down onto a lane with the ever present upper reaches of the cwm nestling the Nant Maesglase at its heart, giving us a wonderful darkened and almost silhouetted view up to the ridge line that we had just followed down.

Survey Result:

Cribin Fawr

Summit Height:  658.7m (converted to OSGM15, Trimble GeoXH 6000) 658.8m (Leica RX1250)

Summit Grid Reference:  SH 79452 15285

Bwlch Height:  566m (spot height)

Bwlch Grid Reference:  SH 78954 15066 (spot height)

Drop:  93m (Leica RX1250 summit and spot height bwlch)

Dominance:  14.09% (Leica RX1250 summit and spot height bwlch)

 

Waun Oer

Summit Height:  670m (triangulation pillar)

Summit Grid Reference:  SH 78556 14786 (hand-held GPS via DoBIH)

Bwlch Height:  549.4m (converted to OSGM15, Trimble GeoXH 6000) 549.6m (Leica RX1250)

Bwlch Grid Reference:  SH 80115 14398

Drop:  120m (triangulation pillar summit and Leica RX1250 bwlch)  

         

Dominance:  17.97% (triangulation pillar summit and Leica RX1250 bwlch)

  

Craig Portas

Summit Height:  603.8m (converted to OSGM15, Trimble GeoXH 6000) 604.2m (Leica RX1250)

Summit Grid Reference:  SH 80154 14120

Bwlch Height:  549.7m (converted to OSGM15, Trimble GeoXH 6000) 550.0m (Leica RX1250)

Bwlch Grid Reference:  SH 80530 14218

Drop:  54.2m (Trimble GeoXH 6000) 54.2m (Leica RX1250)  

       

Dominance:  8.97% (Leica RX1250 summit and bwlch)

 

Mynydd Gartheiniog

Summit Height:  586.3m (converted to OSGM15)

Summit Grid Reference:  SH 80794 14282

Bwlch Height:  552.8m (converted to OSGM15, Trimble GeoXH 6000) 553.1m (Leica RX1250)

Bwlch Grid Reference:  SH 80951 14527

Drop:  33.3m (Trimble GeoXH 6000 summit and Leica RX1250 bwlch) (Dewey and 500m Twmpau status confirmed)

Dominance:  5.67% (Trimble GeoXH 6000 summit and Leica RX1250 bwlch)

 

Mynydd yr Hewyrch

Summit Height:  678.3m (converted to OSGM15, Trimble GeoXH 6000)  678.5m (Leica RX1250) (significant height revision)

Summit Grid Reference:  SH 81697 15003

Bwlch Height:  360.5m (converted to OSGM15, from previous Trimble GeoXH 6000 survey)

Bwlch Grid Reference:  SH 80208 17001 (from previous Trimble GeoXH 6000 survey)

Drop:  318.0m (based on Trimble GeoXH 6000 bwlch and Leica RX1250 summit)

Dominance:  46.87% (based on Trimble GeoXH 6000 bwlch and Leica RX1250 summit) (Lesser Dominant status confirmed) 

 

Maen Du

Summit Height:  675.0m (converted to OSGM15)

Summit Grid Reference:  SH 82237 15172

Bwlch Height:  667.8m (converted to OSGM15)

Bwlch Grid Reference:  SH 81910 15043

Drop:  7.2m

Dominance:  1.07% 
 

For details on the bwlch survey of Mynydd yr Hewyrch

For further details please consult the Trimble Survey Spreadsheet