Wednesday 6 February 2019

Mapping Mountains – Trimble Surveys – Carnedd Llywelyn


10.10.18  Maes Glas Mawr (SH 768 724) and Clytiau Poethion (SH 763 717)  

Maes Glas Mawr (SH 768 724)

Having analysed these two hills with LIDAR I knew before visiting that in all likelihood the subsequent Trimble survey would confirm the summit relocation of Maes Glas Mawr to Clytiau Poethion, with the former becoming a Sub-Twmpau and the latter a new P30.  However, there were reports on the Hill Bagging website that both summits were plagued with gorse, and as I (and the Trimble) do not like gorse it was conjecture if summit data from either hill could be gathered.

LIDAR image of Maes Glas Mawr and Clytiau Poethion

As I parked on the outskirts of the small community of Tyn-y-groes the morning’s sunshine was now turning unseasonably warm with blue skies radiating down and hardly a patch of cloud in the sky.

A public footpath led north-west from the western fringes of Tyn-y-groes toward the summit of Maes Glas Mawr and once I’d done battle with a barb wired fence resulting in another battle scar, this time a bloodied finger, I plodded up toward its summit.

The summit of this hill consists of a steep north-westerly side with the upper part covered in high gorse.  Thankfully the highest point was on the edge of the gorse looking down over the steep flank of the hill, this at least gave a semblance of chance for gathering data.

Implanted in to the summit were the remains of a gnarled gorse bush and by wedging my rucksack in to its wooded lower part and placing the Trimble on top, it gave it elevation above its immediate surrounds, and a relatively secure position to balance atop for the allotted data collection.

The Trimble set-up position at the summit of Maes Glas Mawr

As it beeped away gathering its individual datum points I sat amongst the gorse on a small patch of grass and luxuriated in a restful few minutes bathed in morning sunshine.

Gathering data at the summit of Maes Glas Mawr

Once data were gathered and stored I walked the short distance down to Glyn Uchaf farm where I hoped to make place-name enquiries for the hill.  A note pinned to the door gave instructions to call at the ‘new house’ if there was no reply at the farm.  I proceeded down the track to the new house and knocked on the door, Tomi Owen answered and without a moment’s hesitation invited me in.  Within a few minutes Tomi was offering me a cup of tea, or cold drink and some shortbread.  I spent about 20 minutes with Tomi and he proved a delight to speak with, telling me that the upper field where the summit of this hill is situated is known as Maes Glas Mawr.

A nice way to spend a part of a hill walk


Tomi Owen

Having finished my drink and eaten my shortbread I thanked Tomi for his hospitality and headed down the continuation of the track to a minor road and a footpath through Craflwyn wood, this brought me down to another minor road and a walk up it to try and gain access to the field leading toward the gorse laden summit of Clytiau Poethion.

By now it was beginning to get quite warm and the thought of gorse bashing in shorts and a short sleeved top did not enthuse me, however it needed to be done and my first venture in to the prickly stuff unearthed a rather exotic looking plant.  This is the first time I’d seem such a plant on a Welsh hill, although I suspect there are many more dotted around the landscape.

An exotic looking plant on Clytiau Poethion

Deciding that the summit was not by this spot I backtracked out of the gorse and tried another spot, this again was not the summit, I backtracked and tried a different angled approach but within a few metres I again backtracked.  Fourth time lucky I thought, and this time I followed the grass at the periphery of the gorse to its high point and tried to find a relatively easy way in to the prickly stuff.

The easiest option seemed to be to head toward a prominent telegraph pole and work my way up the ridge toward its high point, I was at last making progress and using the Trimble as a hand-help device I zeroed in to the summit position.  When found it proved to be amongst a mass of very high gorse, I wondered what to do.  Not to be outdone I wondered if I could balance the Trimble on a gorse branch and gather data from this elevated position, and as said branch was positioned over what I judged to be the high point of the hill, it proved a relatively easy way to overcome the difficulty.

The Trimble set-up position at the summit of Clytiau Poethion

As the Trimble gathered ten minutes of data I sat below it, looking up toward it as it balanced precariously like a meerkat standing bolt upright on a slender elevated branch.  I wondered what the data set would be like once processed, but as I seldom carry the 2m pole this unusual surveying position would have to do.

Gathering data at the summit of Clytiau Poethion

The Trimble survived its adventure and once packed away I found an easy way out of the gorse leading me down on a public footpath toward the renovated farm house of Clytiau Poethion.  The land where the summit of this hill is situated is named on the Tithe map as a part of this farm’s land; and not surprisingly the Tithe names this land after that of the farm; Clytiau Poethion.

Looking back toward the summit of Clytiau Poethion

It was only a short walk from here following the minor road to where my car was parked.  My next objective was to visit and survey three hills and attempt to determine which is higher, this is something I’ve wanted to do ever since first listing them many a year ago; Bryn Eithin (SH 775 752), Bwlch Mawr (SH 777 755) and Cae Alen (SH 781 758).




Survey Result:




Summit Height:  108.5m (converted to OSGM15) (confirmed as lower than Clytiau Poethion)

Summit Grid Reference:  SH 76876 72414

Bwlch Height:  87.05m (LIDAR)

Bwlch Grid Reference:  SH 76604 71933 (LIDAR)

Drop:  21.4m (Trimble summit and LIDAR bwlch) (100m Twmpau reclassified to 100m Sub-Twmpau)

Dominance:  19.76% (Trimble summit and LIDAR bwlch)





Clytiau Poethion (significant name change)

Summit Height:  109.1m (converted to OSGM15) (confirmed as higher than Maes Glas Mawr)

Summit Grid Reference:  SH 76337 71799 (summit relocation confirmed)

Bwlch Height:  68.7m (LIDAR)

Bwlch Grid Reference:  SH 77496 72493 (LIDAR)

Drop:  40.35m (Trimble summit and LIDAR bwlch) (100m Twmpau addition)

Dominance:  37.00% (Trimble summit and LIDAR bwlch)










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