Mapping Mountains – Trimble Surveys – Arenig

19.07.20  Foel Fawr (SH 728 392), Foel Fawr (SH 726 394), Pt. 501.4m (SH 730 397) and Pt. 499.9m (SH 731 395)  

Foel Fawr (SH 728 392)

Between Llyn Trawsfynydd to the west and Llyn Conglog Mawr to the east lie a compact group of hills with Graig Wen (SH 739 394) the highest.  These hills are open with few fences and are bounded on the north by an invasive conifer plantation.  The summits overlook many small lakes and pools, each adding depth of variety and perspective to the landscape.  These hills seldom draw me back, but on the times I’ve visited they never disappoint.

Today I met Aled for our first walk together since earlier this year in January.  Covid-19 and its affects have altered many things and one was the travelling restriction which impacted greatly upon visiting the hills.  With this restriction now lifted it was good to be out again with a number of surveys planned.

We met close to Llyn Trawsfynydd and soon had our cars parked at the beginning of the track leading to Llyn yr Oerfel.  Behind the lake our first hill of the day; Foel Fawr, rose in a great bulk of steepening grass.  The continuation of the track led to the Braich-ddu Quarry with a vehicle track on the near moor leading us higher toward the southern ridge of Foel Fawr, and the first of its two 528m twin map heighted summits.

The two Foel Fawr summits with the old prioritised summit position on the left and the new higher summit on the right

This summit has a marvellous backdrop with the higher Eryli peaks lined one after another with the Moelwynion prominent and the distinctive profile of Moelwyn Mawr and Moelwyn Bach rising directly behind the large cairn atop the second and more northerly of the hill’s twin map heighted summits.  Once data were gathered and stored from the first summit and the connecting bwlch we were soon beside the cairn with the Trimble again gathering its allotted data.

The lower cairned summit of Foel Fawr with Moelwyn Bach and Moelwyn Mawr as backdrop

Gathering data from the summit of Foel Fawr

The main objective of the walk was to visit and hopefully survey a forested hill that is given a small 500m ring contour on the Ordnance Survey 1:25,000 Explorer map and a 504m spot height on Magic Maps and on the mapping on the WalkLakes website.  Its connecting bwlch is placed in a rather unsavoury and daunting looking bog.  We had come prepared with a series of ten figure grid references and hoped to take data from each point.

As the Trimble gathered data from the first position, which like all others was in a watery realm, Aled headed in to the conifers armed with an axe.  I then spent the next ten minutes listening to the quiet beep emanating from the survey equipment as each data point was collected and the ever distant crack of branches as Aled carved a way uphill toward the summit.  As he emerged back close to the bwlch he reported that the lower slopes were relatively easy but the higher slopes leading toward the summit were a mess, with numerous wind-blown trees now felled at all angles across the ground.

Gathering data at the first bog survey

Following Aled in to the confines we veered to the right and kept below the wind-blown trees which proved an easier route than the one Aled had investigated on his preliminary foray.  Just before the felled trees were encountered we came upon an unexpected crag, which is quite substantial and now left immersed in the confines of regimented conifers.

The crag leading toward the summit of the new forested Uchaf

The assault course now started, it was never too difficult and soon we had clambered our way over, under and through numerous trees and found the summit just beyond a small area that had direct sunlight breaking through the forest and a view of the sky which gave hope for data collection.  The high point consisted of a flat rock and we quickly devised a system to measure the offset between it and the Trimble placement with it sitting atop my rucksack which was on a conveniently felled tree giving it elevation above its surrounds.  Considering where we were it achieved its 0.1m accuracy level before data should be logged relatively quickly and we sat and chatted as it gathered its allotted data.  Reversing our inward route through the wind-blown felled trees we emerged in to the upright mature forest and contoured around the lower part of the plantation aiming for our next survey in the watery bog.  By keeping in the forest we avoided the impossibility of bog walking which may have proved hazardous!

Aled at the summit with the Trimble

Gathering data on the summit area of the new forested Uchaf

The ten figure grid reference Aled produced for the next survey which was listed as the connecting bwlch for the forested hill, was in the centre of a pool, which made me smile when I pinpointed it on the mapping on the OS Maps website.  As we emerged out of the conifer plantation we were back in the bog, thankfully a semblance of dryish ground led around its reed infested quagmire toward the pool.  I proceeded to set the Trimble up atop my rucksack on a large sponged grass tussock, measured the offset between its internal antenna and the ground at its base and as it beeped away collecting data, I lay across two tussocks close by, and considering the surrounding conditions I remained remarkably dry.

Gathering data beside the small pool

The next point to survey was a 499m map heighted top and Aled encouraged its bwlch to also be surveyed.  This proved to be beside a series of pools glinting blue in the late afternoon sunshine.  Once bwlch data were gathered and stored we headed for the last summit and sat in the warming conditions as another five minutes of data were gathered.

Beside the small lake heading toward the bwlch that connects with Pt. 499.9m

All that remained was another investigation of the bog to our immediate east which connects with Foel Fawr.  We’d already taken two data sets from its waters and with an elevated view we now decided to take two more, one from between the two main large pools which are connected via smaller channels and the last from the edge of the southerly pool.  Considering how horrendous this looked it proved relatively easy to accomplish.

The penultimate bog survey

The route back to the awaiting cars

All that remained was the walk out following a track-bed contouring around the southern ridge of Foel Fawr, which in time connected with our inward route and led back to the track leading to Llyn yr Oerfel.

Survey Result:

Foel Fawr

  

Summit Height:  528.6m (converted to OSGM15) (confirmed as higher than the top positioned at SH 72621 39476)

Summit Grid Reference:  SH 72872 39284 (summit relocation confirmed)

Bwlch Height:  485.5m (converted to OSGM15)

Bwlch Grid Reference:  SH 73074 39525

Drop:  43.1m

Dominance:  8.15%

Foel Fawr 

 

Summit Height:  527.5m (converted to OSGM15) (confirmed as lower than the top positioned at SH 72872 39284)

Summit Grid Reference:  SH 72621 39476

Bwlch Height:  515.0m (converted to OSGM15)

Bwlch Grid Reference:  SH 72815 39394

Drop:  12.6m

Dominance:  2.38% 

Pt. 501.4m 

 

Summit Height:  501.4m (converted to OSGM15)

Summit Grid Reference:  SH 73011 39784

Bwlch Height:  485.5m (Trimble GeoXH 6000 data set spread)

Bwlch Grid Reference:  SH 73105 39632 (from aerial map comparisons)

Drop:  15.9m (Uchaf addition confirmed)

Dominance:  3.17%

Pt. 499.9m 

 

Summit Height:  499.9m (converted to OSGM15)

Summit Grid Reference:  SH 73187 39525

Bwlch Height:  489.6m (converted to OSGM15)

Bwlch Grid Reference:  SH 73419 39616

Drop:  10.3m

Dominance:  2.07%

For further details please consult the Trimble Survey Spreadsheet