Mapping Mountains – Trimble Surveys – Cymoedd Morgannwg

17.04.21  Mynydd Ynys Corrwg (SS 887 979, not Trimbled), Mynydd Blaengwynfi (SS 905 973, not Trimbled), Twyn Crug yr Afan (SS 920 954), Werfa (SS 912 947), Mynydd Caerau (SS 890 944) and Foel y Gelli (SS 881 962) 

Werfa (SS 912 947)

The confines of Abergwynfi and Blaengwynfi are somewhere I rarely frequent.  I’ve only been there once before in April 2003 whilst visiting the five Deweys that surround the two small and connecting villages.  Each connect via a bridge over the Nant Gwyn with Abergwynfi on the southerly bank beside the A4107 road as it speeds its way toward Cymer and Croeserw, and Blaengwynfi on the northerly bank, connected but also separated, similar to an alpine village nestled amongst a stream valley and hills. 

The memories of my first visit were similar to today as the weather on each had beautiful blue sky and pleasant spring warmth.  This I found ironic as the two separated but also connected villages were similar to the 18 year separation between this visit and my last with a connection by the similarity in weather conditions. 

However, whereas my first visit was on my own, today I was with Aled who drove south from Porthmadog meeting me in Caersŵs at 8.15am.  From here I continued the drive south.  We parked just over the bridge in Blaengwynfi and were walking by 10.40am past a myriad of tightly squeezed houses, all lined up one after another. 

The weather was glorious, with just a slight breeze and heat hazed blue sky which was forecast to remain all day.  Heading toward the upper part of the village where the Tunnel Hotel stands forlornly looking out at the tightly packed houses, each person we past said their hellos. 

The start of the forest track

Soon after passing the hotel the paved road turned to a path which soon entered the forestry.  We would now be amongst the conifers for a number of hours.  Aled navigated westward avoiding the easterly approach via a public footpath which when previously visiting our first hill of the day; Mynydd Ynys Corrwg, I had descended and found the footpath a jungle of unsavoury vegetation.  The western approach proved much easier, with a forestry track veering uphill before minor tracks headed toward the hill’s high point.  The summit of Mynydd Ynys Corrwg is placed amongst the conifers, close to an earthen track.  This position is enclosed and although I tried to gather data with the Trimble, it did not achieve the required accuracy level and therefore I closed it down and packed it away. 

Our route continued on the earthen track and then a gravelled track which descended and connected with a main forestry track.  This was less enclosed and gave a semblance of view across the intervening valley toward our last hill of the day; Foel y Gelli. 

Joining one of the main forestry tracks

Below and to our east lay Cwm Gwynfi, the main forest track looped around the upper part of this cwm before heading south toward the top of the second hill of the day; Mynydd Blaengwynfi.  At the head of the cwm Aled wanted to visit a small prominence hill toward the north, one that we had stood on in June two years ago, but had not visited its high point.  This left me continuing on the main forestry path toward a lesser track on the right which headed up to where the trig pillar atop Mynydd Blaengwynfi looks out on a small open section of hill that the planters had the foresight to remain free of conifers. 

I set the Trimble up in three different positions but on each occasion it did not achieve the 0.1m accuracy level before data should be logged and so I closed it down and packed it away without data having been gathered.  During the third attempt to gather data Aled appeared through the trees.  It was good to see him again as we both wondered whether the track leading toward the trig was in fact the correct one! 

The summit of Mynydd Blaengwynfi

Leaving the clearing we met four women on the earthen track, one asked if we were trig baggers.  We stopped and chatted for five minutes before waving our goodbyes, they were the only walkers we met all day, although there were a selection of mountain and trail bikers using the forestry tracks and those on the hills. 

Once back on the main forest track we followed this south-eastward passing the unsavoury looking bwlch of Werfa on the way.  I stopped to take a few photographs as it was this bwlch and its LIDAR height that demoted Werfa from Subhump status and this hill’s summit would later be surveyed with the Trimble.  As I looked at the bwlch I turned to Aled and said ‘praise be to LIDAR’ as the thought of trying to get into such a place of bog and tussock grass to survey its height was not appealing by any means. 

An unsavoury looking place - the bwlch of Werfa

Eventually we reached the earthen track that leaves the main forestry track which headed to open hillside and once through the gate designating the boundary between each we stopped.  I was thankful for the rest and after hours submerged in conifers on forestry tracks it was a relief to be out in the open again. 

To our south was the summit of Twyn Crug yr Afan and between us and it was parched dead grass bleached in the sunlight and tracks across the intervening moor, with softened underfoot going that was pleasing, and which made the going easy. 

Heading toward the summit of Twyn Crug yr Afan

The summit of Twyn Crug yr Afan has an ancient tumulus on it and the discarded remains of what looks like some form of Ordnance Survey column.  As I placed the Trimble atop my rucksack to gather data, Aled headed off to visit another lower prominence hill which I had surveyed in July 2016. 

As the Trimble quietly beeped away gathering its individual datum points I stood below the tumulus close to a fence.  Nothing seemed to stir, an occasional sound of a car would emerge out of the quiet as it headed over the near road, but I was left to enjoy the quiet surrounds and look out and up at the blue sky.  My slumbered mind was soon disturbed as two trail bikers emerged over the moor; I flagged them down and asked which path was best to connect up with the track leading to the top of Werfa, which they had come down a few minutes before.  One instantly pointed toward the track Aled had used to head off to the lower prominence hill, whilst the other instantly pointed toward the other track that seemed to head lower down toward the road.  We all laughed.  They then told me the latter track swung around and connected across the road to the continuation of the track leading up to the mast on the summit area of Werfa. 

Gathering data at the summit of Twyn Crug yr Afan

I was soon heading down to the road and then up the track toward the next survey of the day; the connecting bwlch of Twyn Crug yr Afan, this and its summit along with that of Werfa were the only ones on the walk without current LIDAR coverage.  The bwlch proved difficult to pinpoint as the connecting valleys lay diagonally across the track and not at 90° to it.  The area where its critical point lay also had slight undulations in the ground.  However, having spent a number of minutes assessing the lay of land I picked the spot for Trimble placement and set the equipment up to gather data and then retreated to a conveniently placed foot stile where I sat and waited.  Just before the five minutes of data were gathered and stored Aled came walking down the track. 

Gathering data at the bwlch of Twyn Crug yr Afan

Once the equipment was packed away we continued up the access track to the fenced off outer realms of the mast compound that adorns the summit area of Werfa.  Beyond the compound is the trig pillar which also marks the summit of this hill.  I placed the Trimble aligned with the highest part of the grassy surrounds beside the trig pillar and scribbled all necessary detail in my surveying notebook as it gathered its allotted data. 

Gathering data at the summit of Werfa

We still had a few miles to cover and a track on the parched moor led us in the direction of the next bwlch which connects to Mynydd Caerau.  Between it and the bwlch was about a mile of open hill.  The path intersected with another which contoured westward in one direction and headed toward our next bwlch in the other.  Soon the bwlch came into view nestled between steep hillsides.  A further data set was gathered from this bwlch with data produced via LIDAR favoured for both its height and position.

The continuing route to the summit of Mynydd Caerau was horrendously steep.  I very slowly plodded up it; Aled soon disappeared into the distance above me as a darkened silhouette against the sun.  I stopped on occasion and took the opportunity to take a few photos as the afternoon light became rich with colour, at contrast to the morning’s light which had been washed out by an overhead sun.  However tiring the ascent was and I found it very tiring and especially so for the last five minutes plod toward the trig pillar, the light and surrounds compensated. 

Werfa from Mynydd Caerau

LIDAR gives the summit of Mynydd Caerau positioned amongst reed grass consisting of the remains of an ancient tumulus which is now partly flattened.  We both thought that ground beside the trig pillar looked as high, but I placed my trust in LIDAR as it’s rarely mistaken on an open hill. 

Gathering data at the summit of Mynydd Caerau

As the Trimble gathered data we both sat with boiled eggs and pick and mix as the order of the day.  The walk was beginning to take its toll and rests were beginning to get more important and definitely needed.  Once the Trimble was packed away I followed Aled as he headed off toward one of the near wind turbines hoping that an access road would connect with the main access track near to the bwlch which had just been surveyed.  It didn’t, but it was only a short walk down the hillside to connect with it.  We followed the track down close to the bwlch between Mynydd Caerau and Werfa and then left it as it started to regain height, and headed over grass and down toward the bwlch connecting with our last hill of the day; Foel y Gelli. 

Mynydd Caerau from Foel y Gelli

This hill had stared back at us and looked distant for much of the day, and even now seemed disconnected from the hills just visited.  It is after all an outlier and proved a wonderful hill to end on top of as it gave extended views and looked back on the hills visited during the day.  However, getting to it proved a tiring head down slog.  Thankfully a good sheep path exists all the way and I slowly followed Aled as he made good progress up its slopes. 

Werfa from Foel y Gelli

As the Trimble was positioned on the summit it slowly ebbed down to its 0.1m accuracy level before data should be logged, I stood and looked out across the hills.  Lengthening shadows and lowering sun give beautiful conditions when on the hill and the last two hours had also given dramatic light with the deadened and bleached moor grass an ever appealing colour, quite succulent and at contrast to the manicured greens of reclaimed grazing land. 

Gathering data at the summit of Foel y Gelli

Mynydd Blaengwynfi

Having packed the Trimble away we reversed our inward route to a collapsed wall which we followed steeply down to a foot bridge which led us to the road beside the first houses in Abergwynfi.  From here it was only a short walk through the streets down to the awaiting car which was a pleasure to get to after 8hr 4omin on the hill. 

 

Survey Result: 

 

Mynydd Ynys Corrwg

Summit Height:  502.4m (LIDAR)

Summit Grid Reference:  SS 88703 97997 (LIDAR) 

Bwlch Height:  460.0m (LIDAR)

Bwlch Grid Reference:  SS 89474 98558 (LIDAR)

Drop:  42.4m (LIDAR)

Dominance:  8.44% (LIDAR)

 

 

Mynydd Blaengwynfi

Summit Height:  527.5m (LIDAR)

Summit Grid Reference:  SS 90598 97360 (LIDAR)   

Bwlch Height:  488.7m (LIDAR)

Bwlch Grid Reference:  SS 90636 98471 (LIDAR)

Drop:  38.8m (LIDAR)

Dominance:  7.36% (LIDAR)

 

 

Twyn Crug yr Afan

Summit Height:  560.2m (converted to OSGM15) (significant height revision)

Summit Grid Reference:  SS 92035 95448   

Bwlch Height:  526.0m (converted to OSGM15)

Bwlch Grid Reference:  SS 92019 95054

Drop:  34.2m

Dominance:  6.11%

 

 

Werfa

Summit Height:  567.5m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SS 91274 94767 (Trimble GeoXH 6000)   

Bwlch Height:  479.9m (LIDAR)

Bwlch Grid Reference:  SS 91189 97075 (LIDAR)

Drop:  87.5m (Trimble GeoXH 6000 summit and LIDAR bwlch) (Subhump deletion)

Dominance:  15.43% (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

 

Mynydd Caerau

Summit Height:  555.3m (LIDAR)

Summit Grid Reference:  SS 89082 94451 & SS 89084 94448 (LIDAR)    

Bwlch Height:  465.4m (LIDAR)

Bwlch Grid Reference:  SS 895619 94779 (LIDAR)

Drop:  89.9m (LIDAR)

Dominance:  16.20% (LIDAR)

 

 

Foel y Gelli

Summit Height:  449.6m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SS 88147 96211 (Trimble GeoXH 6000)   

Bwlch Height:  395.8m (LIDAR)

Bwlch Grid Reference:  SS 88935 96025 (LIDAR)

Drop:  53.8m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  11.97% (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

 

 

For further details please consult the Trimble Survey Spreadsheet