Mapping Mountains – Trimble Surveys – Mynydd Epynt and Mynyddoedd Duon

18.08.15  Allt yr Esgair (SO 126 243) and Waun Fach (SO 215 299, only bwlch surveyed)   

The summit of Allt yr Esgair (SO 126 243)

Having visited and surveyed the critical bwlch of Pen y Fan (summit at SO 012 215) which is situated in a field on the outskirts of Talerddig which nestles beside the A470, I now wanted to survey the critical bwlch of Allt yr Esgair (summit at SO 126 243) / Waun Fach (summit at SO 215 299), as these two points are where the topographic and geographic Regional split of Wales are to be found.  The latter bwlch is complicated as contour interpolation suggests that it is hard to distinguish which bwlch is applicable for Allt yr Esgair, and likewise for Waun Fach.

The bwlch for Pen y Fan is the Regional split between North Wales and that of Mid and West Wales, the bwlch I now wanted to examine is the point where this Regional split divides Mid and West Wales from that of South Wales

This second dividing point is complicated as it has two distinct options for where it is situated, they are positioned north-westward / south-eastward of one another, and between the two is Allt yr Esgair, which at a listed 392m high and having a prominence of 203m is a relatively large lump of a hill.  In essence not knowing which of these two bylchau is the higher / lower means that Allt yr Esgair is either joined to the hill group of Mynydd Epynt to its north-west or to the hill group of Mynyddoedd Duon (Black Mountains) to its south-east, the former would have this hill firmly placed in the Region of Mid and West Wales, whilst the latter would have the hill firmly placed in the Region of South Wales.  It was my intention today to solve this riddle.

As I drove south the weather was set fair for the day with a beautiful blue sky and just a hint of a weak breeze.  I parked next to a house in the small community of Pennorth (SO 112 260), this is where the north-westerly of the two bylchau is positioned.  However, this north-westerly bwlch has two options for its position as there is an intervening contour on current Ordnance Survey maps that manifests itself like a small island when on the hill to hill traverse, therefore both sides of this contour would need to be surveyed, and to over complicate an already complicated situation there is a disused railway line that cuts through the landscape on the periphery of Pennorth and obliterates part of this intervening contour when it does so.

I had examined this area in detail in a Google Car and the westerly option for this north-westerly bwlch seemed to be situated on the road as it headed north through Pennorth, whilst the easterly option for this north-westerly bwlch was positioned in a field, my main concern was the field as this time of year an arable crop could be growing in it which would complicate matters even more, but access to the field was proving difficult to find as I had driven the Google Car all around the country lanes that are positioned next to this field and all I could see were thick and overgrown hedges, there seemed no access to the place where I wanted to survey.

As I locked my car I walked up the lane past the houses in Pennorth and looked at the land on the hill to hill traverse, this went up in both and opposite directions toward driveways to the front of houses,  I continued up the lane to look back toward my car, the lane looked almost flat but a few metres in front of my car seemed to be the high point on the valley to valley traverse, this was conveniently placed beside a pull-in spot where I could park my car and within a couple of minutes I had re-positioned the car and the Trimble was placed on its roof as the confines of the houses and front gardens with their manicured hedges meant that elevation for the surveying equipment was the order of the day.

To gain elevation I used my car as an unusually shaped and improvised tripod

As the Trimble ebbed down to its 0.1m accuracy I stood in the shade looking at my car which was now acting as an improvised and very odd shaped tripod, once the accuracy level had been achieved I pressed ‘Log’ and stood back for its allotted five minutes of data collection.  During this time the small community of Pennorth went about its business with one or two cars and a tractor passing on the lane or close to it.

Gathering data at the western point of the north-westerly bwlch option in Pennorth

Happy that one option for this important bwlch had been successfully surveyed I re-positioned my car back in its original parking place and walked around the corner to the bridge that spans the old railway, I’d noted when I had driven past this spot that there seemed to be access over the stone parapet of the bridge onto the disused line, the first place I looked over made me shudder as there was an almighty vertical drop down into a multitude of undergrowth, however a few metres further on and the land on the other side of the bridge was level with that of the road and just beyond this was a fence which would give me access into the field, I was in luck!

Within a few moments I was over the parapet and fence and into the field which was large, green and thankfully without any arable crop growing in it.  At the far northern end of the field was Tŷ-gwyn farm and between me and it there were a few sheep lazing around in the sun.  Everything seemed quiet and the high hedge between the field and the road would hide me from view of any passing vehicles, whilst hanging branches and such like next to a fence adjacent to the land of the disused railway line would hide me from view of the farm.  I quickly assessed the lay of land and within a few minutes the Trimble was placed on top of my rucksack and a 0.42m offset measured and I crept back to my hidey hole and waited for the 0.1m accuracy level to appear, once it did I pressed ‘Log’ and scampered back out of view.

At the eastern point of the north-westerly bwlch option with Allt yr Esgair in the centre background

When five minutes of data were collected I pressed ‘Done’ and closed the equipment down, took a few photos and quickly clambered over the fence and parapet back onto the lane, within a few minutes I’d sorted my gear and was driving toward the south-easterly option for the position of this Regional and important bwlch.

Gathering data from the field on the east side of the outskirts of Pennorth with the farm of Tŷ-gwyn in the background

When I approached the outskirts of the rather aptly named community of Bwlch (SO 148 220), my heart sank as the field where my previous inspection in a Google Car and where map contours indicated the bwlch to be positioned had an 8ft high Maize crop growing in it, this was not ideal but all was not lost as the A40 which passes over this bwlch in a hill to hill direction may have obliterated the natural bwlch, and therefore I knew that at least one data set would have to be taken from this road, this at least would give a height for this position and one that could then be compared to the two I had just gathered from the bwlch at Pennorth.

As the traffic whizzed past I put the Trimble on the stone wall above the grass verge beside the road and stood back to assess the lay of land hereabouts, this seemed a good position but the road seemed almost flat for a number of metres and therefore if time allowed I wanted to take another data set a few metres from the current position of the Trimble, this would give me a comparison of heights.  Before pressing ‘Log’ I looked over the stone wall down into a mass of brambles which looked at least 3m below me, and further below was the Maize crop, my estimation was that the road was about 3-5m higher than the natural ground where the Maize crop was growing.  I was also worried about the position of the Trimble as it was perched above bramble hell and one slight wobble and it would be airborne visiting the blackberries below, I just hoped that it would remain where it was for the next few minutes, to give me peace of mind I wedged a tiny stone at its side to stop any wobble and inclination to go blackberry picking, pressed ‘Log’ and stood back and waited on the grass verge as cars and lorry’s thundered past.

Gathering data from the stone wall with the field full of Maize below

As the five minute data collection ended I whizzed back to the Trimble, took a few photos and quickly grabbed it before it plummeted over the edge.  I now rigged up my rucksack on the metal rail next to the stone wall and positioned the Trimble on top of it; this would give me a second data set from a position that vied for the low point of the grass verge beside the road as it sped its way on the hill to hill traverse. 

The Trimble set up on my rucksack on the metal stanchion leading to the stone wall with the field full of Maize beyond

The Trimble set up position for the second data set beside the road with the expanse of the Maize crop in the background

After the equipment was packed away I visited the Maize crop and walked down through it toward where the road veered up overhead, it really was much higher than the ground in the field.  The Trimble is a remarkable piece of equipment and has in-built technology given the name of ‘Floodlight’ which helps ‘satellite shadow reduction’, this enables the equipment to gather data when satellite coverage is restricted, and I decided the environment of a high Maize crop may be ideal to put it to the test.  But this could wait until after I visited the summit of Allt yr Esgair.

On the periphery of the Maize crop

Before doing so I investigated the ground immediately to the south of the busy A40 as there was an outside chance that higher ground existed here when compared to the field where the Maize crop was growing, if so the land to the south of the road would be where the natural bwlch was positioned.  The access to this southern land was difficult as there was a hedge, brambles and nettles and a big drop from the edge of the road which was lower on its southern side when compared to its northern side, I wandered up and down the southern grass verge beside the road and peered down through the undergrowth and decided that all of the land continued downhill toward where a small pool is indicated on current Ordnance Survey maps.  However, this visual inspection was not thorough and I decided to have another look after visiting the summit of Allt yr Esgair.

Allt yr Esgair has well marked paths ascending its two ridges; these ridges can be walked up directly from each bwlch where I had been happily pottering around for the last couple of hours.  I had decided to examine the south-easterly bwlch option last enabling me to visit the hill from this direction.  Leaving the joys of the Maize field behind I walked up a peaceful narrow lane to where a footpath sign indicated my onward route, this onward route proved rather magical as an arch has been made where dappled light radiates through the overhead canopy.

Entering Narnia

Beyond the magical archway the land opened up with the sun beating down onto a sleepy summer landscape where high hills loomed over freshly cut grass and farm vehicles busied themselves making hay, this summer scene left me with the feeling that it was good to be out on the hill.  The path continued ever upward with the distinct profile of the Beacons towering over the pastoral beauty of green field and valley bottom.  What a beautiful part of Wales this is.

Looking over summer fields to the Mynyddoedd Duon beyond

Pen y Fan, distinct in profile and impressive as ever

I was surprised when I reached the summit as I thought there would be more uphill, four people had passed me on their way down shortly before I had reached the high point, but as I positioned the Trimble aligned with the uppermost bit of the highest embedded rock at the summit and as it quietly collected its 300 allotted data points I stood with the summit and seemingly the hill all to myself.

Gathering data from the summit of Allt yr Esgair

As the Trimble was packed away I stood and looked at a commemorative slate plaque embedded in a stone wall that formed part of a small seat, the plaque was dedicated to the memory of Eirene Baroness White of Rhymney, and I thought it rather lovely and unobtrusive.

The commemorative plaque and inbuilt seat

Retracing my inward route I waved my hello’s to a farmer as he marched his tractor around an adjacent field cutting the high summer grass, it seemed that the sun and the buoyancy it brings had pervaded all around.  Very soon I was back at the natural arch with its gentle shade and fluttering shadow.  Nearing my car and the busy A40 my thoughts now concentrated on the Maize crop.

The shadowed profile of part of the Mynyddoedd Duon

Back through the arch

Once back beside the road I walked to the stone parapet and noticed that about seven rows of Maize into the field lay a slight clearing where the Trimble stood a chance of achieving its 0.1m accuracy level before data should be logged.  The word ‘clearing;’ is relative as this part of the field was still covered in Maize, but it was just a wee bit less densely packed than the rest of the field.  Without further hesitation I headed into the Maize crop to luxuriate myself in its 8ft-10ft high fineries, this really would be fun!  I walked down its edge and then straight into it and found the less densely packed runnel of land quite easily and walked down to the point on the hill to hill traverse that was the lowest, here I placed the Trimble on my rucksack to give it a semblance of elevation above the ground and the long wait to achieve its 0.1m accuracy began.

Nearing the low point on the hill to hill traverse with bramble hell next to me and the stone wall beside the road up on the right

Having entered the Maize I walked down the runnel that had a semblance of a clearing and positioned the Trimble on top of my rucksack at the runnel's low point

I’ve experienced these long waits on a number of occasions in the past, but never where one is completely immersed in Maize, so much so that the outside world almost disappeared.  I ventured back to the Trimble every five minutes or so to check on its downward progress and very soon there it was, the magic 0.1m, I pressed ‘Log’ and scampered back up the runnel and waited until the five minutes of data collection was complete.

The Trimble set up position at the low point of the runnel

Gathering data from the first of two points in the Maize field

Happy that at least one data set had been collected from the field I then went in search of where my estimated position for the bwlch actually lay, this was a ten figure grid reference obtained by centralising the position of the hill to hill contours on the Ordnance Survey enlarged Geograph map.  By using the Trimble as a hand-held GPS unit I pushed my way through the Maize and completely disappeared from view, it now seemed the whole world was made of Maize and nothing except for this field and its crop existed, and so it remained so for the next 30 minutes, as once I had pinpointed my preferred position I again placed the Trimble on top of my rucksack and waited to see if it could gather data.

This proved a long wait and one that I was only too happy to undergo as my present position was rather funny, I had never done anything like this before and enjoyed it immensely, although the word ‘immensely’ is relative, as surveying in Maize fields is not the norm and too much enjoyment from doing so may have people in white coats knocking on my front door to cart me away.

My view of the world during the long wait for the Trimble to achieve its required accuracy on the second data set

Eventually I pressed ‘Log’ and scampered back to a safe distance as this remarkable piece of kit did its stuff, it’ll be interesting to see how good, or bad, these last two data sets are, as both positions had restricted vision.

Gathering data from the second of two points in the Maize field

Before heading off to bag some Pedwarau hills I had one last look at the ground to the south of the A40 road, again I wandered back and forth and tried to find a safe access point to it, but all seemed impenetrable at this time of year and the land looked as if it continued downhill, indicating that the position of this south-easterly bwlch was either on the road or more likely to be in the field full of Maize.

Survey Result:

Allt yr Esgair

Summit Height:  392.6m (converted to OSGM15) (Trimble GeoXH 6000)

Summit Grid Reference:  SO 12611 24354 (Trimble GeoXH 6000)

Bwlch Height:  189.2m (LIDAR, remaining natural ground at base of land-filled road bridge, with LIDAR contouring implying that the old natural height of this bwlch was 189.8m positioned at SO 14233 22525)

Bwlch Grid Reference:  SO 14238 22539 (LIDAR, remaining natural ground at base of land-filled road bridge, with LIDAR contouring implying that the old natural height of this bwlch was 189.8m positioned at SO 14233 22525)

Drop:  203.4m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  51.81% (Trimble GeoXH 6000 summit and LIDAR bwlch)

Waun Fach

Summit Height:  810.6m (LIDAR)

Summit Grid Reference:  SO 21559 29991 (LIDAR)

Bwlch Height:  186.3m (LIDAR)

Bwlch Grid Reference:  SO 11290 26157 (LIDAR)

Drop:  624.3m (LIDAR) 

Dominance:  77.02%

For further details please consult the Trimble Survey Spreadsheet click {here}