Wednesday, 31 May 2017

Mapping Mountains – Trimble Surveys – Y Berwyn

04.05.17  Bwlan (SH 946 255)

Bwlan (SH 946 255)

Bwlan sits on the east south-eastern ridge of Cefn Coch (SH 923 266) as it descends in to the wild heather moor.  It probably has few visitors, and yet it has a serene beauty the landscape of moor can only give, a wildness of openness where windswept land and the spring calling of Skylark is interspersed with distant views and a quality of peacefulness seldom experienced.

I’d visited Bwlan once before in May 2005 when I used a basic levelling technique (BLS) to determine its drop value, resulting in 51ft 6˝ (15.7m) of drop which was sufficient for its inclusion in the fledging list of the Yr Uchafion, however Bwlan has two options for its critical bwlch with an intermediary 523m map heighted bump between each, and as I’d only surveyed from one bwlch option to the top of this bump and then added 5m to the drop measurement to equate for the difference between the 523m spot height and the 528m spot height given to the summit of Bwlan, it meant the measurement was open to inaccuracy.

In recent months Aled Williams has been producing a multitude of results via LIDAR data, one being to Bwlan, resulting in a 526.1m summit and a 512.6m bwlch height, giving this hill 13.55m of drop.  However, the data produced by LIDAR only covered the ground for one of the two bylchau, therefore we wanted to visit this hill and Trimble each bwlch and the summit and compare the Trimble, LIDAR and the BLS data and confirm the status of Bwlan.

I met Aled in the car park at the northern end of Llyn Efyrnwy after he’d quickly visited the summit of Foel y Garnedd (SH 942 267), with a strong easterly wind blowing it gave land further west uninterrupted blue skies and as I waited for Aled the cloud cover began to break and by the time he had arrived and we’d got our boots on and driven up the road to the start of a forest track, the sky had turned a succulent blue.

It was good to be out with Aled again and we chatted away as we walked on the track past the old house of Fedw-ddu and continued up through the conifer forest on the southern edge of the Afon Nadroedd.  The track proved a convenient way to visit Bwlan and took us within a few metres of the 523m map heighted bump at SH 940 258.  Across the moor the high Aran dominated the view; they really are impressive hills, a bulk of a ridge firmly planted in the landscape, with moorland summits and ridges extending west from their high land.

The high Aran

The options for the bwlch position of Bwlan lay west and east of the 523m map heighted bump and as its summit was no more than a minute or so from the track we headed upward to Trimble it first.  As the Trimble gathered its data Aled headed off to assess the lay of land at the westerly bwlch that I had not surveyed 12 years ago and that LIDAR data does not cover.

Gathering data at the top of the 523m map heighted bump which came to 522.3m (converted to OSGM15)

Aled assessing the lay of land at the westerly bwlch

Once the Trimble was switched off and packed away I made my way down through the moor grass and heather and joined Aled at the westerly bwlch, we proceeded to take two data sets in the area of this bwlch, both in small channels on the hill to hill traverse.  During the time that the Trimble beeped away gathering its data we sat on the moor chatting as the breeze blew, Skylarks sang and the high Aran peered back from many a mile away.

An unusual view of Foel y Geifr, Trum y Gwragedd and Foel Goch with the slither of road crossing Cwm Hirnant on the right

Our next survey was the eastern bwlch which Aled had assessed using LIDAR data, and as I followed him, he used the Trimble as a hand-held GPS to take us to the position of the bwlch given by LIDAR, again this proved to be in a boggy channel.  Before setting the Trimble up we both assessed the lay of land and decided that with confidence of the LIDAR position that only one data set was required at the area of this bwlch.

Gathering data at the eastern bwlch which proved to be the critical one for Bwlan

Next stop was the summit and Aled repeated the process using the Trimble as a hand-held GPS, once on top we stomped around to find the firmest land that we judged to be the highest and I then proceeded to set the Trimble up to gather another data set.

Gathering data at the summit of Bwlan

Although the beauty of such hills as Bwlan can be in their solitude and openness, our planned descent route was past Pistyll Rhyd-y-meinciau, which is a series of waterfalls in the Afon Eiddew as it tumbles down toward Llyn Efyrnwy, and it was the prospect of visiting this waterfall that I suspected would add to the beauty of Bwlan.

Leaving the summit of Bwlan we walked south-eastward over rough moor to where a gate gave access on to high grazing land which had the comfort of grass and the prospect of easier walking for our descent, before doing so I took one last data set from the high point on the eastern end of the summit ridge of Bwlan which has a 525m map spot height.  As the Trimble gathered its data we lay in the sun and chatted about Aled’s upcoming stag night in Dublin, oh to be young again!

Once data were stored and the Trimble packed away we followed a fence down toward the ruin of Blaen-y-coed which in its time must have been a substantial building.  Below us the Afon Eiddew trickled on its descent, a wide stream discoloured with peat.  According to the map a path followed the steam on its northern side down to the forest corner where a track would take us back toward the car, however the path was almost non-existent and the further we progressed the bleached tussock grass grew larger, if a path existed we were not on it and although we scanned the ground ahead we could not see any sign of it.  It was then that we came across the first of five waterfalls, all radiant with the sun gleaming across their speckled water as it trickled downward on its never ending journey.

This house must have been a remote and desolate place to have once lived

The ruin of Blaen-y-coed above the Afon Eiddew

The Afon Eiddew below the ruin of Blaen-y-coed

As we approached the first waterfall we spotted a path on the southern side of the steam and looking down we saw that it continued, with just tussock grass and steepening slopes and no sign of a path on the northern side we decided to cross the stream, this proved a wise decision as the next half an hour was superb as one waterfall fell in to the next and the path zig-zagged its way down beside the stream giving access to each pool under each waterfall, it was a magical experience with the added bonus a small scramble down rock where the path had no other option than a vertical descent.

Aled crossing the Afon Eiddew

This is the waterfall below the point where we crossed the stream

Just one of a series of waterfalls that form Pistyll Rhyd-y-meinciau

Aled admiring one of the waterfalls

Pistyll Rhyd-y-meinciau

This photograph gives perspective as Aled looks up at one of the waterfalls

The path beside the waterfalls is highly recommended, it is narrow in places and sometimes ill-defined and has on occasion plummeting drops, but is well worth investigating.  As we left the last waterfall we continued downward to stepping stones across the river at the base of the falls and stopped and chatted with three people who were sitting in the sun.  As Aled talked with a woman who grew up in Blaenau Ffestiniog and now lived with her husband in Llanbrynmair, I talked with their friend who had travelled from London to be with them for a few days to get away from the chilled weather plaguing the east of England, during our conversation he told me that he sometimes practises faith healing and I half-jokingly mentioned my wonky right knee, a couple of minutes later and he was clasping my knee and working away faith healing its wonkiness.

Looking back toward Pistyll Rhyd-y-meinciau

It must be an impressive and frightening sight when in full spate

It was good to meet these people and enjoy conversation in the sunshine; leaving them we followed the well maintained path back toward my awaiting car as the southern bulk of Bwlan rose framed at the northern end of Llyn Efyrnwy, a great little hill, can’t wait for the Trimble results. 

Bwlan (SH 946 255)

Survey Result:


Summit Height:  525.9m (converted to OSGM15) (significant height revision)

Summit Grid Reference:  SH 94692 25540

Bwlch Height:  512.1m (converted to OSGM15)

Bwlch Grid Reference:  SH 94179 25714

Dominance:  2.62% 

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