Thursday 9 May 2019

Mapping Mountains – Trimble Surveys – Y Llethr


17.11.18  Clip (SH 654 329), Craig Ddrwg (SH 656 331), Pt. 594.2m (SH 656 337), Pt. 579.2m (SH 657 342), Moel Ysgyfarnogod (SH 658 345) and Foel Penolau (SH 661 347 and SH 661 348)   

Moel Ysgyfarnogod (SH 658 345) and Foel Penolau (SH 661 347 and SH 661 348)

There are many upland places in Wales that have special qualities, but the northern Rhinogydd is an area that cannot be matched.  It is a land where rock strewn crag and moor meet.  It is a complicated land where the profusion of rock up thrusts, many with steep slopes and sheer cliffs would add unwanted adventure if clag and mist descends to its summits.

Aled and I ventured in to this land and planned a traverse of it northern hills from Clip to Foel Penolau, and with a forecast of November cloudless skies we hoped that this would give us sufficient daylight hours and suitable weather to visit all the summits, and with the Uchafion as the benchmark this would mean eight in all.

As we followed the moorland track toward the abandoned old farmhouse of Wern-fach most of north-west Wales bathed in clear skies with dark silhouettes of hills following our car journey south.  However, this part of the country steadfastly clung on to low cloud that grasped the tops and worrying for us especially so for this part of the Rhinogydd.  There are few places in Wales where I have promised myself not to venture when mist enshrouds the hills, and this is one.  But with the forecast of any low cloud clearing we hoped that this would take place before we reached the ridge and the final steep ascent of our first hill of the day; Clip.

Glimmers of clear sky to our east gave hope that the clag would rise, and as we followed the moorland path from Wern-fach beside the Afon Crawcwellt patches of sunlight illuminated the lower hillsides, with intense colours against the moor.

Early morning clag as we approach the northern Rhinogydd

The path proved wet with many small bog infested brooks to jump or delicately wade over.  As height was gained the clag seemed to descend and as we continued below the great bulk of Craig Ddrwg we were in mist.  However, as the clag started to envelop us large ripped tears above showed blue sky and the increasing strength of the wind whipped the morning mist upward and past us as it quickly rolled up the adjacent hillside.

The view east with the first glimmer of sunlight

We were now at the bwlch between Clip and Craig Wion and watched as the shrouded world around us was quickly exposed, with Rhinog Fawr to our south dominating the distant view, its summit clear to the heavens and yet delicate mist banks meandered around its lower slopes.

Rhinog Fawr

From here a steep path led to Bwlch Gwilym and the ridge that would now occupy us for the remaining daylight hours.  Our arrival on the ridge was perfectly timed as the northern part was still being ripped of its morning clag whilst immediately to our south Clip rose against blue sky.

I slowly followed Aled to the summit of Clip, stopping on the way to join him as he shouted over ‘brocken spectre’, and there below cast against the whipped mist was a coloured halo, appearing and then quickly disappearing as the mist was pushed away from the mountains.  Reaching the summit we were met by strengthening wind which complicated surveying and also at times communication.  Thankfully this lessened as we progressed on the ridge and only increased again as we reached the higher summits further north.

The summit of Clip is easily identified and as with many of these high points, consists of rock.  The Trimble was soon perched on its high point and gathering data; the first of eighteen data sets taken during the next five hours.

Gathering data at the summit of Clip

Once data were stored I packed the Trimble away and we headed down to its connecting bwlch which proved easy to identify.  Once there, I quickly assembled the Trimble on top of my rucksack, with this acting as an improvised tripod, and measured the offset between its internal antenna and the ground at its base and waited until the allotted data were gathered and stored.

We knew that at least 15 data sets would be taken during the day, some of which were prioritised as their respective summits were marginal, others were not directly associated with the status of the hill and realising that daylight hours were against us many of these non-priority surveys would be reduced in time from the usual five minute data set to the minimum two minutes that Trimble recommend.

Our next hill of the day; Craig Ddrwg consists of two summits, with the southern being one metre higher on the map, and as we approached its profile thrusted upward in a pile of rock, it was a stunning view, and now accentuated as I imagined we would be in thick clag on this part of the ridge, and as it was now clear my mind relaxed and was enhanced with the feeling of wild openness these hills give.

Craig Ddrwg (SH 656 331)

The high point of Craig Ddrwg is placed about eight metres from a cairn and the Trimble was soon wedged in place aligned to its highest point and beeped away gathering its allotted data.

Gathering data at the summit of Craig Ddrwg

The mist had now completely cleared from these hills and the view north was stunning, with rock carved hill and mountain lake dappled in the morning sunshine screaming out to be investigated.

The wild beauty of Craig Ddrwg

Our next planned bwlch survey consisted of two potential critical points, and reaching these, assessing the lay of land in their heathered depths and then taking the two data sets would probably add thirty minutes to the days surveying, and as this would impact upon surveying Foel Penolau we decided that this bwlch could be left for another day.  This proved the only bwlch that we did not survey on this part of the ridge and as the afternoon progressed and daylight hours slowly ebbed away it proved a wise decision.

The next hill was another carved in rock with its summit easily identified and very soon Trimbled.  The surveys were now coming thick and fast with barely a moment to relax between each one.

Gathering data at the summit of Pt. 594.2m (SH 656 337)

Yr Wyddfa

Its connecting bwlch was in shade and placed in wet land just to the east of Llyn Du, it was soon Trimbled and once data were gathered and stored and the equipment packed away we headed up to the summit of our next hill.  During Aled’s place-name research he gathered names for all these hills, but these names will wait until the Yr Uchafion list is published, so for now their names will be documented under the point notation.

Flat bedded rock with gauged out fissures led pavement like toward the bulbous summit of our next hill which is given a 578m map height.  It was a sheer joy to be on this ridge in these conditions with the mornings clad a thing of memory and low angled sunlight flowing over the hills.  Away to our north the higher Eryri peaks floated skyward, whilst the high Aran and Arenig were now sun bathed, their ridges edged against the sky.

The fissured slabs of our next hill to survey

Gathering data at the summit of Pt. 579.2m (SH 657 342)

Only one survey remained before we tackled the two higher peaks of Moel Ysgyfarnogod and Foel Penolau and this was the next connecting bwlch which is the critical bwlch for the higher of the two Craig Ddrwg summits, and it was positioned in a large expanse of wet land.  Once data were stored we headed upward on grassed hillsides which are at odds with the rest of these hills, leading to the trig pillar atop the highest hill of the day; Moel Ysgyfarnogod.  By the time I reached its summit I felt knackered.

The untidy cairn beside the trig pillar swarmed outward toward a small rock outcrop which is the high point of the hill.  As the Trimble gathered data I sat with Aled beside the trig eating a banana, the first food I’d had all day.

Gathering data at the summit of Moel Ysgyfarnogod (SH 658 345)

Foel Penolau from Mowl Ysgyfarnogod

All that remained was the survey of Foel Penolau, this hill has a complicated bwlch consisting of a boulder field and two tops given the same 614m map height.  To do this hill surveying justice would take time, and thankfully we had sufficient daylight hours remaining to complete the survey.

On our way toward the hill Aled suggested that I should take a data set from where the 588m spot height appears on the Ordnance Survey Interactive Coverage Map hosted on the Geograph website, this is taken as the height and position of the connecting bwlch for Foel Penolau by some, giving it 26m of drop, but the 5m contouring on OSMaps indicates the critical bwlch is placed in the boulder field at the base of the hill’s vertical southern cliff, and interpolation of these contours gives this hill nearer 30m of drop.

I quickly set the Trimble up at the first bwlch position and once data were stored, packed it away and we headed to the boulder field.  It is this boulder field that John Kirk first hypothesised on whether a col should be viewed from the prospective of an ant or a human; as the south facing cliff of Foel Pelolau has deposited large boulders at its base over many years and if a person used these to connect on the hill to hill traverse the hill would have less drop compared to taking the ground below the boulders as that for the bwlch.  We had already debated this by the time we arrived and the two of us agreed that if there were gaps below and between the boulders we would treat this bwlch like an ant and take the height of the bwlch to land at the base of the boulders. 

The boulder field is placed directly below the vertical southern face of Foel Pelolau, this is an impressive place and one that I had not visited for many years.  We started to examine the base of the boulders that stood steadfast in the positions that they had fallen, huge lumps of rock with gaps between and daylight peering under many of them.

This bwlch is not an easy place to judge where its critical point lies, but Aled soon followed the course of land between the boulders from where the grassed hillside to the south enters the boulder field on the hill to hill traverse and there were gaps under many of the larger boulders indicating to us that it is the ants viewpoint that should be followed in determining where the critical bwlch of this hill lies.

Having judged our best position for this hill’s critical bwlch I placed the Trimble on top of the boulder above it and Aled climbed down in to the gap at its side and we measured the offset between the ground at its base and the Trimble’s internal antenna, and then waited for five minutes of data to be gathered and stored.

Measuring the offset

During data collection Aled headed up the near vertical cliff and found a route through to its easier upper part, and then peered back down at me as I sat behind the boulder with the Trimble beeping away gathering its allotted 300 datum points.

Once the Trimble was packed away I slowly plodded up the steep boulder field as it cascaded down from the upper part of Foel Penolau, and joined Aled on the southern summit of the hill.  The Trimble was soon aligned with its high point and data being gathered.

Gathering data at the southern summit of Foel Penolau (SH 661 347)

Dropping steeply off its summit to the bwlch between it and this hill’s northern summit we now surveyed the bwlch between its two tops and sat in a natural wind shield with a rock carved seat and roof as the Trimble gathered its penultimate data set of the day.  All that remained was the last of eighteen data sets to be taken from the summit of the northerly top.

We were soon at its high point and as the Trimbe gathered data Aled investigated the northern route off the hill and came back reporting that he had found a path.  Closing the Trimble down and packing it away I stood for a moment and looked south at the profiles of these hills silhouetted against a lowering sun.  I didn’t want to leave, but knew I would.

Gathering data at the northern summit of Foel Penolau (SH 661 348)

Aled admiring the view toward Yr Wyddfa

The route down was good, although boggy in places and we soon connected with the track that leads down toward the farm of Cefn Clawdd, from here it was only a short walk to where Aled’s car awaited.  It had been a good nine hour day on the hill, with eighteen data sets taken and a number of marginal hills surveyed. 

As Aled drove back to Porthmadog I sat in his car and relaxed.  I was tired and my legs ached, but these were periphery to the inner glow that such a day on the hill had given me.


Postscript:

As the connecting bwlch of Foel Penolau consists of a boulder field that complicates the position of its critical point I wanted to re-visit and take further data sets on the valley to valley traverse.  By doing so I hoped that all eventualities would be covered.

Therefore, nine days after visiting the hill with Aled I headed to the northern Rhinogydd again, never a bad thing to find oneself doing!  The weather forecast was good with little breeze and low cloud breaking up and sunshine predicted for the afternoon.

I walked in from the west following an old quarry track leaving the minor dead end road close to the last farm of Cefn Clawdd.  As I travelled west toward these hills I’d passed through rain and low hill cloud, and although their tops were clear when I set off banks of murk slowly rolled westward and I knew I would probably be in mist whilst doing at least part of the survey.

The approach toward Foel Penolau on the second survey

The surveys concentrated on the boulder field and I wanted to build up a series of surveyed points on the valley to valley traverse heading from west to east.  This would give a good rendition of the lay of land and importantly its height.  I’d also brought my digi-camcorder as this would be able to document the land of the boulder field much better than any photograph.

Height was soon gained and once the track gave up its forlorn route I headed up toward a small weather beaten gate giving access to the open, upper part of Moel Ysgyfarnogod.

Looking out toward Rhinog Fawr

Wanting to visit the summit of the two 2,000fts I followed the narrow path up toward the small rock outcrop a few metres from the trig pillar at the summit of this hill.  All around was November murk, with odd glimmers of light breaking through the upper cloud base.  It was remarkably still and quiet, seemingly without anyone for miles around.

Early morning mist gathering around Yr Wyddfa

I filmed a quick introductory video from beside the summit and then headed down to where the Ordnance Survey Interactive Coverage Map hosted on the Geograph website places the 588m spot height which has been taken as the height of the critical bwlch for Foel Penolau by some.  When visiting this point with Aled he wisely suggested I take a data set from this position, this proved to be 50 metres from the position of the spot height, and therefore I now wanted a second data set from this area.  However, this land is higher on the hill to hill traverse compared to the land of the boulder field.  Once the survey was completed I headed toward the boulder field where I then spent the next two hours.

I’d left three small rocks in situ on the boulder where the previous bwlch data set had been taken, and these were still in place and easy to find, I placed two flags at this point as I wanted to take a series of data sets leading over the boulder field and then take a video showing each Trimble set-up position and the land between and under the boulders.

The next data set I wanted to take was where the hill to hill traverse enters the boulder field, and even through there is lower ground on this traverse amongst the boulders it would give a height to the last bit of grass as it disappears and is swamped by the rocks.

As I descended toward the boulder field I visually placed where the land on either side of the opposing valleys definitely went downhill, and placed a flag at the eastern point and began the first valley to valley survey at the western point.

This first survey from the innards of the boulder field consisted of wedging my rucksack in to the boulders and placing the Trimble on top of it, the measurement offset to the gap at the base of the boulder was 1.88m.

The whole area was a mass of jumbled boulders and I wanted to take at least four further data sets slowly working eastward.  The second of these surveys had the Trimble firmly wedged in place on a pointed boulder.  By now banks of mist were rolling across the hill adding an atmospheric surreal element to proceedings.

One of many Trimble set-up positions in the boulder field

The third position heading east through the valley to valley traverse was where Aled and I had taken the bwlch data set from nine days ago, I placed flags at this point and continued through the boulders.

At this point I took a break and filmed a video showing the flags and boulder field including some of the deep gaps between the rocks.  Having packed the digi-camcorder away the fourth Trimble set-up position was on a boulder with a 1.68m measurement offset taken to the ground below.  Each of these offsets were being taken to the ground at the base of the gap below these boulders, in affect I had become an ant for the day and was taking a series of measurements based on how an ant would traverse this land.

The fifth position again had my rucksack wedged in place between boulders and the Trimble placed on top of it.  The measurement offset was 1.91m and a five minute data set was taken.  During all these data sets the banks of mist would slowly descend and then thin.  I was now nearing the end of the boulder field and just had one more data set to take.

The last data set had the Trimble placed on the top of another pointed boulder with a 1.81m measurement offset.  All except for one of these data sets were marked with flags, and before leaving the bwlch I wanted to take another video showing their placement and the lay of land.  Gathering all the flags I then headed up on the jumbled cascade of boulders toward the first of the two Foel Penolau tops.

The last Trimble data set taken in the boulder field

Arriving on the southern top glimmers of brightness was now breaking through toward the east.  I’d brought the lightweight tripod and antenna to take a series of summit photos with the Trimble in position and set this up on the high point of the southern top.

Descending to the gap between the two tops I then headed up to the most northerly summit.  When I arrived the murk had been pushed away and a beautiful late November sky with lowering sun and glimmers of light heralded a fantastic end to the day’s proceedings.

Before leaving the summit I again assembled the Trimble attached to its external antenna which was placed on its tripod.  I seldom have need to use the Trimble connected to its external antenna, but always enjoy seeing it assembled this way.

At the northern summit of Foel Penolau (SH 661 348)

All that remained was to descend the cascade of boulders and head toward the small gate and down to the wet track and back toward by car.  It had taken just under six hours for the walk and a further seven data sets had been taken to add to the two bwlch data sets and two summit data sets taken whilst with Aled, and all these surveys will give a good rendition of the drop value of Foel Penolau. 

Foel Penolau
     
  
Survey Result:



Clip 
 
Summit Height:  595.3m (converted to OSGM15) (confirmed as lower than Craig Ddrwg [SH 65659 33162])

Summit Grid Reference:  SH 65460 32942

Bwlch Height:  564.0m (converted to OSGM15)

Bwlch Grid Reference:  SH 65551 32999

Drop:  31.3m (Dewey, Dodd and 500m Twmpau status confirmed)

Dominance:  5.26%





Craig Ddrwg

Summit Height:  597.3m (converted to OSGM15) (confirmed as higher than Clip [SH 65460 32942]

Summit Grid Reference:  SH 65659 33162

Bwlch Height:  544.2m (converted to OSGM15)

Bwlch Grid Reference:  SH 65765 33950

Drop:  53.0m

Dominance:  8.88%





Pt. 594.2m 
 
Summit Height:  594.2m (converted to OSGM15)

Summit Grid Reference:  SH 65671 33789

Bwlch Height:  567m (based on 26.7m BLS)

Bwlch Grid Reference:  SH 65703 33662

Drop:  27m (based on 26.7m BLS)

Dominance:  4.49%





Pt. 579.2m  

Summit Height:  579.2m (converted to OSGM15)

Summit Grid Reference:  SH 65744 34211

Bwlch Height:  557.3m (converted to OSGM15)

Bwlch Grid Reference:  SH 65583 34422

Drop:  21.9m (500m Sub-Twmpau status confirmed)

Dominance:  3.78%





Moel Ysgyfarnogod

Summit Height:  624.0m (converted to OSGM15)

Summit Grid Reference:  SH 65843 34588

Bwlch Height:  c 442m

Bwlch Grid Reference:  SH 65877 29986 (I)

Drop:  c 182m

Dominance:  29.17%





Foel Penolau

Summit Height:  614.4m (converted to OSGM15) (twin summit status confirmed with 614.379m and 614.380m respectively, with 1mm difference the Trimble is unable to split these tops)

Summit Grid Reference:  SH 66145 34774 and SH 66184 34832

Bwlch Height:  582.5m (converted to OSGM15)

Bwlch Grid Reference:  SH 66099 34735

Relative Bwlch Height to each summit:  604.5m (converted to OSGM15)

Relative Bwlch Grid Reference to each summit:  SH 66154 34788

Drop:  31.9m (600m Sub-Twmpau reclassified to 600m Twmpau) (Subsimm reclassified to Simm) (Subhewitt reclassified to Hewitt)

Dominance:  5.19%







No comments: