Thursday 19 May 2022

Mapping Mountains – Trimble Surveys – Tarren y Gesail


21.03.22  Bryn Dinas (SN 646 999) and Corlan Fraith (SH 630 000)

Corlan Fraith (SH 630 000)

With a high pressure system to the east of the country giving relatively settled and dry conditions, I headed toward the small community of Bryncrug, which is positioned to the north-east of Tywyn.  From here a narrow dead end road makes its way in to the hills following the course of the Nant Braich-y-rhiw.  Where the paved section of road ends its course continues as a rough track.  This is where I parked my car and soon had my spring fleece coat, thin gloves and ear warmer on as the easterly breeze chilled proceedings.

Although the forecast was for settled conditions, the sky was not ablaze with blue, it was leaden with no hint of direct sunlight.  Leaving my car I headed on the rough track with the stream below to my right and white dots of sheep nested on the steepening slopes either side. 

The track leading to the hill

The track made steady progress ever upward, with the slopes of Corlan Fraith; my second and last hill of the walk, rising steeply to my immediate south.  My first hill of the day; Bryn Dinas, was not yet in view and it was this hill that was my main surveying objective of the day as its drop is close to 30m.

Parts of the track could easily be driven in a car, but other parts were rough and waterlogged where only a 4x4, a quadbike or tractor could make progress.  The track leads up to a bwlch which is unnamed on contemporary maps and continues meandering eastward.  This was the area for my first survey.

I had come prepared with a ten figure grid reference for the bwlch taken from interpolation of 5m contouring.  Maps show an ancient cairn which is given a 317m spot height on the contemporary Ordnance Survey 1:50,000 Landranger map.  Between it and the track was a flattish area, although from my vantage point the cairn could not be seen and I wondered if it had now been overgrown by moor grass and heather.

Having spent a few minutes assessing the lay of land and gaining height to look down on the area of the bwlch, I decided that the best place to take data from was the high point of the track, which as this point forms a slight cutting.  Therefore, I backtracked to it and set the Trimble up atop my rucksack and after noting the measurement offset between its internal antenna and the ground at its base I set it to gather data. 

Gathering data at the bwlch of Bryn Dinas

Once five minutes of data were gathered and stored I closed the equipment down, took a few photographs, packed it away and headed to the summit of Bryn Dinas.  This consists of two moss laden tops, about three to four metres apart.  I assessed these from a number of directions and having decided which one looked higher I set the Trimble up and sat on heather below the equipment whilst it gathered data. 

Gathering data at the first grassy knoll at the summit of Bryn Dinas

I had considered combining Bryn Dinas and Corlan Fraith in an extended circuit taking in the hills to the south using Cwm Maethlon as the central hub.  From the summit of Bryn Dinas I now looked out to these hills with the land situated close to Llyn Barfog looking particularly wild and welcoming.

As I admired the view I decided to take data from the second mossy top, and soon had the Trimble set up gathering its third data set of the morning.  During data collection I again sat on heather and looked out toward the continuation of my route down to the connecting bwlch with Corlan Fraith. 

Gathering data at the second grassy knoll at the summit of Bryn Dinas

Land hereabouts could be a wild affair to walk through if not for the tracks and paths leading across the moor and thankfully for today’s onward progress a green track led from just below the summit of Bryn Dinas toward the bwlch of Corlan Fraith.  I found this satisfying, both in its ease of passage, but also in the environment I was now walking in.  Even though the blue skies normally associated with a high pressure system were not forthcoming, and even though my fleece coat, ear warmer and thin gloves were still being worn, I found this land appealing, quiet in its nature and probably seldom visited except for a farmer, a rogue walker or a hill bagger.

I soon arrived at the bwlch and spent a number of minutes assessing the lay of land.  The bwlch was extensive and my positioning of the Trimble could easily be out by a number of metres.  When LIDAR is available for this part of the country all will be revealed, but as I was now here I chose my spot and set the equipment up to take another data set. 

Gathering data at the bwlch of Corlan Fraith

Once data were gathered and stored I packed the equipment away and headed up the eastern slopes of Corlan Fraith.  The initial going was over moor grass which formed a foreground of bleached colour giving way to steepening slopes of grass and moss.  By the time I reached the ridge leading up to the summit the easterly wind blew across the upper hill. 

Bryn Dinas from the ascent of Corlan Fraith

Once on the ridge a fence line led toward the summit of Corlan Fraith.  The high point of the hill is festooned with a large cairn that has a thin plinth built on it, more rock in the shape of a cairn is placed on top of the plinth and a wooden post pokes its way out of this latter cairn.  The point I judged to be the highest natural ground was conveniently positioned on the leeward side of the cairn, giving some shelter for my rucksack and the survey equipment.  I soon had it set up and placed a rock either side at its base to keep it firmly in place. 

The Trimble GeoXH 6000 set-up position at the summit of Corlan Fraith

During data collection I sat on rock on the other side of the cairn, out of view of the equipment so as not to hinder satellite reception, and scribbled all necessary information in my notebook whilst the wind whipped across the upper hill.  It was a marvellous place to sit and get slightly chilled. 

Gathering data at the summit of Corlan Fraith

My descent route followed the fence line I had used leading to the summit, and then continued beside it down through occasional bog, before steeply plummeting down to the stream below.  This was definitely a leg wobbler; I stopped on occasion and looked back up, and was thankful that my route for the day was not done in reverse as this would have been a lung buster to get up! 

Looking down on the track I took earlier in the morning toward Bryn Dinas

At the bottom of the steep section I easily crossed the stream and walked the short distance to the track I had used earlier in the morning, this gave easy passage back to my car where I met one of the local farmers who had driven up to release sheep on to the hill.  This proved a pleasant meeting and I smiled during our conversation as he was concerned with one of his two dogs, who menacingly circled me looking for a nip of one of my legs.

After the farmer left I changed in to dry clothes, during which spots of rain whisked across the land.  Thankfully this did not herald even a shower and the rain that did fall felt refreshing to be out in. 

 

Survey Result: 

 

Bryn Dinas

Summit Height:  345.6m (converted to OSGM15)

Summit Grid Reference:  SN 64662 99930

Bwlch Height:  315.8m (converted to OSGM15)

Bwlch Grid Reference:  SH 64694 00067

Drop:  29.8m (Trichant reclassified to Sub-Trichant)

Dominance:  8.62%

 

 

Corlan Fraith

Summit Height:  406.3m (converted to OSGM15)

Summit Grid Reference:  SH 63078 00086

Bwlch Height:  303.0m (converted to OSGM15)

Bwlch Grid Reference:  SN 63749 99934

Drop:  103.3m

Dominance:  25.43%

 

 

For further details please consult the Trimble Survey Spreadsheet

 

  

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