Saturday, 24 June 2017

Mapping Mountains – Trimble Surveys – Elenydd

10.05.17  Cyrnau Mawr (SN 751 750), Craig Lan Las (SN 758 747), Pt. 413.9m (SN 767 751) and Lan Lwyd (SN 761 752)

Craig Lan Las (SN 758 747)

I wanted to take advantage of the settled weather in the west of the country before predicted low pressure systems brought their more unsettled conditions toward the end of the week, and decided to visit four hills to the south-east of Pontarfynach (Devil’s Bridge).  I’d contemplated visiting these hills for a number of years but had never done so, when studying maps and potential ascent routes I’d always thought that an ascent from the Arch on the former Hafod estate would be the best, but as Aled’s continuing analysis of LIDAR data had found a new 390m Double Sub-Pedwar in Cyrnau Mawr (SH 751 750) an ascent of this hill and its adjacent 400m Sub-Pedwar of Craig Lan Las would make a good circuit from the west when joined with the two Pedwar hills to the north-east with the Nant Brignant being central on this small horseshoe.

There aren’t many options to park a car for convenient access to the public footpath that leads toward Cyrnau Mawr, but thankfully a pull-in spot next to a letterbox was ideal.  As I walked up the earthen track the sky radiated blue and with just a breath of breeze the prospect for the day ahead and the surveys I planned on conducting was excellent.

I left the track and walked up the closely cropped grassed south-western slopes of Cyrnau Bach to the trig pillar positioned close to the fence boundary where a conifer plantation swamps the northern side of this and its adjacent hill; Cyrnau Mawr.

Ordnance Survey maps give Cyrnau Mawr a small 390m uppermost contour ring straddling the forest boundary fence, whilst LIDAR data gives the high point as 391.4m and approximately 23 metres to the south of the edge of this contour ring in amongst land between 380m – 390m.  When I approached it was obvious that the LIDAR position for the summit of this hill was correct.

Having set the Trimble up on top my rucksack I stood back whilst it gathered its customary five minutes of data and looked toward my next hill; Craig Lan Las, the underfoot conditions were wilder on this hill with bleached tussocks portraying what is common on the Elenydd hills.

Gathering data at the summit of Cyrnau Mawr

Surveys would come one after another on this walk with four summits and three or four bylchau to visit, and the first of these bylchau lay just to the east and firmly implanted in a bog.  All of the points I planned on surveying had been analysed with LIDAR data by Aled and I had come prepared with each ten figure grid reference, but I also wanted to independently assess each survey position and compare these to where LIDAR data indicated each should be, and on the critical bwlch for Cyrnau Mawr my estimated bwlch position was within a few metres of where LIDAR indicated the true bwlch was, I trusted LIDAR and placed the Trimble at the point that Aled had noted.

Gathering data at the critical bwlch of Cyrnau Mawr

After packing the Trimble away I slowly made my way up the steepening western slopes of Craig Lan Las to two tops, each high point consists of thick grass with the bleached and dry land of tussock grass all too evident all around.  I took data sets from each top, both attractive slender affairs in a land of flatly rounded summits.

Gathering data at the first and slightly lower of the two tops of Craig Lan Las

Gathering data at the second and slightly higher of the two tops of Craig Lan Las

Beyond the summit of Craig Lan Las lay its connecting bwlch with Lan Lwyd, this proved a delight and consisted of heather, tussocks and an odd rouge conifer gaining growth in a big bog.  Approaching the bwlch I had a good view of how the land slightly rose toward where the valley to valley traverse met and headed that way, some of the underfoot conditions proved unusual as my leg occasionally disappeared down beyond where I thought the ground lay, this place must be seldom visited as any prospective hill bagger would no doubt circumvent the delights of this bog.  I used the Trimble as a hand-help GPS and let it guide me toward the spot where LIDAR data placed the critical bwlch, once there I set the Trimble up on top of my rucksack and proceeded to sit on a clump of relatively dry heather as it gathered five minutes of data.  My view from the heather was one where the Trimble was only just visible as the heather and bog had almost swallowed the whole of my rucksack.

Lan Lwyd with the connecting bwlch (bog, a big bog, a bigger than a big bog) between it and Craig Lan Las looking decidedly unwelcoming

The view of the Trimble from my heathery perch

Gathering data at the critical bwlch of Craig Lan Las

During this first part of the walk I had contemplated my way down, should I backtrack the way I had come or leave the adjacent summit of Lan Lwyd until the last and follow its western ridge to connect with a track leading toward the conifer plantation beside the Nant Brignant, I decided on the latter as I didn’t want to visit the tussock laden bog again.

Once out of the bog I followed a green vehicle track toward the bwlch connecting Lan Lwyd with another Pedwar to its east, it was blissful to be on good walking ground again, but it had also been good to experience a small part of wildness that these hills now only have in small patches as much of their land has been reclaimed for grazing.

Pt. 413.9m from the green vehicle track that approaches its bwlch

The green track turned in to a graveled track at the bwlch and after the Trimble had gathered another five minute data set, this time perched on top of a thick gate post with a 1.36m measurement offset between its internal antenna and the ground below, I continued following the course of the track toward the summit of the next hill which is given the point notation as it is unnamed on Ordnance Survey maps and local and historical research has not yet unearthed an appropriate name for it.

Gathering data at the critical bwlch of Pt. 413.9m

I proceeded to take two data sets, one from the hill’s southern top which is placed in a closely cropped grazing field and one from its higher northern top which is placed in a felled forest consisting of scrub undergrowth intermingled with the remains of felled trees.  As the Trimble gathered data I looked below me and the Arch beside the B 4574 road was only a few minutes’ walk away, this is where the critical bwlch for Lan Lwyd (the highest and last of the four hills I planned on visiting during the day) lay, and as the track descending to the conifer plantation next to the Nant Brignant originates next to the Arch I could follow it after collecting data beside the road.

Gathering data at the summit of Pt. 413.9m

With this revised descent route now firmly established I packed the Trimble away and retraced my route back on the track toward the summit of Lan Lwyd, the high point was beside a section of land set aside with daffodil bulbs, as indeed were swathes of the hill’s south-eastern slopes.  Once the customary data set was gathered I regained the track and followed it down to the B road and the arch.

Craig Lan Las from nearing the summit of Lan Lwyd

Gathering data at the summit of Lan Lwyd

The Arch was constructed in 1810 by Thomas Johnes of Hafod to commemorate the Golden Jubilee of George III.  The road used to pass under the Arch, but after a lorry damaged hit and damaged it the road has now been diverted, creating what LIDAR data gives as a new position for the critical bwlch of Lan Lwyd.

Beside the Arch is a large car park and a number of trails heading off in to adjacent woodland, it’s usually a sleepy place, especially so on a blue skied day when the pace of life seems to slow even in a place where the pace of life is probably forever quiet and slumbered.

Initially I judged the low point on the hill to hill traverse to be on the southern side of the old road a couple of metres to the east of the span of the Arch, the Trimble took ten minutes or so to attain its 0.1m accuracy level before data should be logged, during this time I chatted with a couple who had just completed one of the marked trails through the woodland, after they headed toward their car I spent quite some time looking at the lay of land between the old and new road and the earthen embankment between, most of the time I judged the old road to be lower, but the LIDAR grid reference gave the southern part of the new road as that for the critical bwlch.  It was only after I used my camera viewing window as a level that the new road looked slightly lower than the old road, I then placed the Trimble beside the new road and hoped that any passing car would avoid a Trimble fatality.

Gathering data at the first and slightly higher of the two bylchau of Lan Lwyd

Considering where the Trimble was placed it achieved its 0.1m accuracy level relatively quickly and as it beeped away gathering its 300m allotted datum points only one car passed which was fortunate both for satellite coverage and for the safety of the equipment.

Gathering data at the second and slightly lower and critical bwlch position of Lan Lwyd

Looking back at the Arch and the bwlch of Lan Lwyd

This was the eleventh and last survey of the day and I packed the Trimble away happy in the knowledge that these hills had now been analysed with LIDAR data and surveyed with the Trimble with a mass of resulting data to salivate over!

The track proved a delight to follow as it made its way over the broad and undulating western ridge of Lan Lwyd, and down toward the old farm house of Brignant-uchaf, this is now left to the elements but is still relatively intact although a part of its roof has recently given in to age and struggle.  Today the old house nestled in its stream valley a forgotten edifice where once people would have worked and played.  I looked through an open window inside to debris, a fire place sat forgotten amongst the remains of an iron bed frame with a wall and the ceiling gaping open.  It was bathed in welcoming sunlight today, similar to a multitude of other lonely Welsh farm houses dotted across the land, some still active, others laid bare and slowly rotting, today the remains of Brignant-uchaf is a relic to times now gone.

Craig Lan Las from the track leading to the old farm house of Brignant-uchaf

Brignant-uchaf is now abandoned to the elements

Inside the living room of Brignant-uchaf


The track left the old farm house and I followed it through a gate and in to the conifer forest where it ended in a large gravelled area, the continuation of the path through the woodland was narrow and welcome and bathed in afternoon warmth and eventually brought me out on to open lower hillsides, where another track emerged taking me down to the B 4343 and a short walk on its tarmacked surface back to my awaiting car.

The path through the forest

Survey Result:

Cyrnau Mawr

Summit Height:  391.4m (converted to OSGM15)  

Summit Grid Reference:  SN 75154 75006

Bwlch Height:  369.8m (converted to OSGM15)

Bwlch Grid Reference:  SN 75342 24906

Dominance:  5.52%

Craig Lan Las

Summit Height:  439.8m (converted to OSGM15)

Summit Grid Reference:  SN 75828 74735

Bwlch Height:  414.7m (converted to OSGM15)

Bwlch Grid Reference:  SN 76025 74951

Drop:  25.2m

Dominance:  5.73%

Pt. 413.9m

Summit Height:  413.9m (converted to OSGM15)

Summit Grid Reference:  SN 76757 75119

Bwlch Height:  381.7m (converted to OSGM15)

Bwlch Grid Reference:  SN 76691 75174

Drop:  32.2m (Pedwar status confirmed)

Dominance:  7.78% 

Lan Lwyd

Summit Height:  445.4m (converted to OSGM15)

Summit Grid Reference:  SN 76171 75270

Bwlch Height:  378.0m (converted to OSGM15)

Bwlch Grid Reference:  SN 76517 75545

Drop:  67.4m

Dominance:  15.13% 

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