Mapping Mountains – Trimble Surveys – Y Llethr

04.06.15  Crib y Rhiw (SH 663 248), Diffwys (SH 661 234) and Pt. 643.2m (SH 648 229) 

Diffwys (SH 661 234)

Out today with John and Graham with the southern Rhinogydd planned as our destination.  Our main aim for the day’s surveying was Diffwys which is listed by Alan Dawson as a Submarilyn with 148m of drop, as 150m is the qualifying mark for Marilyn status; this hill had been on our prioritised list of hills to survey for a number of years.

We met in Bala and took one car down to Bont-ddu and turned right toward the hills on a narrow road that gained height and parked at its end at SH 656 201, where three cars can easily be left.

The weather was blissful with clear blue skies and good clarity of colour, however it was warm which no doubt would make us suffer on the up hills.  The last time I had spoken to one of the local farmers in this area he had told me that the path that leads up the Braich had been churned up by trail bikes and in places it now resembled a stream.  It is only a matter of a few metres to the gate that leads onto this path from where the car had been parked and confronting us as we approached the gate was a police sign warning everyone to ‘slow down’.  I wondered if this was an act of humour or perhaps a sign put there to try and discourage the trail bikes.

The sign at the start of the path

I set off before John and Graham and tried my utmost to set a reasonable pace up the path as it gained steady height onto the open hillside of the ridge leading upto the hill that the Nuttalls list as Diffwys West Top.  But my pace was slow, partly because of the heat but also the weight I was carrying, as a camera, video camera and the Trimble weight 10lb, added to this was a large tripod and a 75 litre capacity rucksack to strap the tripod onto, within the rucksack were the usual things required for a day in the hills, all of this adds weight, and added weight means a slower pace.

Even though I puffed on the uphill the views compensated as Diffwys looked resplendent with its southern arm stretching out over Craig Aderyn, the hill was bathed in morning sunshine with the shadowed cloud movement giving depth to the landscape.

The shapely profile of Diffwys

Soon John and Graham approached and slowly overtook me as we all headed up the Braich and once at its top we crested the western ridge of Diffwys and swung right following a good path beside a dilapidated wall and a double fence.  We now had a decision to make as we could either survey this western top and then continue to the summit and then the bwlch of Diffwys and descend on a green track beside the Afon Cwm-llechen, or we could traverse the western bulk of Diffwys and survey its bwlch first and use our inward route as our descent and survey this western top later in the afternoon, we decided upon the latter option.

Graham and John just about to catch and overtake me

The continuation of the southern Rhinogydd down to the Afon Mawddach and the sea

Continuing over the hill that the Nuttall's name as Diffwys West Top

By now it had really warmed up and all I wanted to do was stop and take the weight off my shoulders.  The traverse of Diffwys was new to me; I had never done this before and found the prospect of venturing onto new ground to be partly stimulating in my ever increasing state of weariness.  We initially followed a sheep track as it contoured its way around the hillside; this seemed to disappear as we approached a section of wet ground, this traverse was proving fun as it gave a marvellous viewpoint across Llyn Bodlyn to the rounded bulk of Moelfre with the elongated arm of north-west Wales stretching out to Ynys Enlli beyond.

Traversing the western flank of Diffwys

The rounded profile of Moelfre with Llyn Bodlyn in the foreground

Heading toward the bwlch of Diffwys

This route also gave a different viewpoint toward Y Llethr and Crib y Rhiw with Llyn Dulyn nestled under the crags of the latter hill.  Occasionally I would catch upto John and Graham as they waited for me; we had now rounded the western shoulder of Diffwys and could see its bwlch ahead of us.  Between it and us was varied ground with copious amounts of bilberry, rock and a number of small ridges to clamber over and around.  Progress was being made and soon we were walking on the flatland beside small pools just on the western side of the hill’s bwlch.

Y Llethr and Crib y Rhiw with Llyn Dulyn in the foreground

Typical Rhinogydd ground of rock, lake and dramatic views

The critical bwlch of Diffwys is the right hand notch of the two on the left of the photo

Crib y Rhiw from near to its connecting bwlch with Diffwys

Once over the ridge wall that strides between these hills we arrived at the bwlch, and the level was set up with John taking readings to the staff that Graham was holding, I tried to recover and stood on an intervening small ridge taking photos down onto proceedings.  The bwlch had two options for its critical point, the one nearest Diffwys proved to be the lower and soon the Leica GS15 was set up and gathering data.

Using the level and staff to survey for bwlch position

The Leica GS15 set-up at the critical bwlch of Diffwys

To our south Diffwys looked proudly grand with the wall robustly stretching toward its summit, in the opposite direction lay Crib y Rhiw with its rocky grassed flank looking eloquent in shape and appealing to the eye.

Diffwys from its critical bwlch

The connecting solid wall stretching upto Crib y Rhiw

We took a measurement offset between the critical bwlch and that of an elevated rock outcrop and gathered five minutes of Trimble data to compare results against that of the Leica GS15.

I now wanted to visit the summit of Crib y Rhiw and keep my totals for these three Nuttalls on par with one another.  I also wanted to gather data from its summit as to my knowledge no spot height has ever appeared on any map for the high point of this hill.  As I wearily plodded up the path that leads to its summit Graham remained at the bwlch with the equipment and John set off behind me and soon passed me.

Y Llethr from the summit of Crib y Rhiw

The high point of Crib y Rhiw is at the southern end of its summit ridge, once I stumbled my way upto it I placed the Trimble on a small embedded rock at the summit and gathered five minutes of data.  During this John headed north to examine another high point and once there looked back to where I was, we both concluded that the high point of the hill was at the southerly end of its ridge.

Gathering data with the Trimble at the summit of Crib y Rhiw

By the time we arrived back at the bwlch the hour data collection for the Leica Gs15 was almost complete, we just had time for John to do a couple of minutes to the video camera before the equipment was switched off and packed away.  The next uphill proved utterly debilitating as it was so warm and without any form of breeze.

The uphill from the bwlch to the summit of Diffwys was a slow, hot grind.  I stopped on many occasions and tried to recover my breath as I took photos back toward Y Llethr and Crib y Rhiw and over toward the shapely profile of Moelfre.  Slowly progress was made, but it was at a cost as the sun was taking its toll.  I have experienced the sun’s debilitating effect when out in the hills on a number of occasions and can feel its piecing, unrelenting strength that saps all forms of energy, I also know that to make progress I have to take it very steady and just aim ahead to a set point and when reached to take a rest, and then repeat this until the summit is reached.

Crib y Rhiw from the ascent of Diffwys

Moelfre from the ascent of Diffwys

The last few hundred metres to the summit of Diffwys was a wobbly affair, as although the path was good and the ridge was relatively flat I still had to rest and gasp for air.  Eventually I reached the trig point, got the rucksack and camera and Trimble off my shoulders, unstrapped the tripod and then flaked out on the ground.  During this John and Graham were taking readings on either side of the ridge wall and pinpointing the high point of the hill to be about five metres to the north of the trig point.  All I could do was groan on the ground and occasionally stumble to my feet and take a photograph.

The weary, hot plod up Diffwys

John using the mini tripod and level to take readings from the top of the wall at the summit of Diffwys

Taking readings on the eastern side of the wall at the summit of Diffwys

We took data with the Leica GS15 at the high point and another five minutes of Trimble data to the top of the trig, having taken a measurement offset between the summit and the trig.  Ahhhhhh, time to rest, eat, take on water and try and recover.

The Leica GS15 set up at the summit of Diffwys

The Trimble gathering data at the top of the trig pillar on Diffwys

Once an hour of data had been collected the Leica GS15 was packed away and we headed down to the connecting bwlch with the hill that the Nuttalls list as Diffwys West Top.  I collected data with the Trimble from this bwlch and then joined John and Graham at the hill’s summit.

Gathering data at the bwlch of the hill that the Nuttall's list as Diffwys West Top

By the time I arrived at the summit John was taking readings with the level and Graham had the staff in hand and had positioned a row of flags across the plateaued summit area.  A few minutes later and we had pinpointed the high point to be 4 metres from where a small cairn has appeared over recent years.  We moved the cairn to the high point and took a data set with the Trimble.  All that remained was to descend back to the awaiting car.

Using the level and staff to ascertain the high point of Pt. 643.2m

Gathering data from the top of the small cairn

The descent proved rather beautiful as early evening light had broken through the western high cloud that had pushed in over the last hour of the walk.  This gave a delicate feel to the landscape and highlighted the hills in a diffused and welcome light.

On our way down

Delicate evening light on Diffwys

As I passed the old marker stone close to the end of the path I stopped and took a few photographs and looked back toward Diffwys as it stood grandly on display, ahead of me over the Afon Mawddach lay Cadair Idris with the evening light striking and highlighting its northerly cirque of cliffs.

The old marker stone

Cadair Idris bathed in evening light

These mountains are special in their beauty; they are testaments to the ravages of the past when glaciers once carved out the land and left sculptured ridges and high cymoedd which are now inherent in the landscape.

Survey Result:

Crib y Rhiw

Summit Height:  681.3m (converted to OSGM15) (significant height revision)

Summit Grid Reference:  SH 66368 24868

Bwlch Height:  652.1m (converted to OSGM15) (from subsequent Trimble GeoXH 6000 survey)

Bwlch Grid Reference:  SH 66080 25302 (from subsequent Trimble GeoXH 6000 survey)

Drop:  29.2m

Dominance:  4.28%

Diffwys

Summit Height:  750.4m (converted to OSGM15, Trimble GeoXH 6000) 750.4m (converted to OSGM15, Leica GS15)

Summit Grid Reference:  SH 66127 23413

Bwlch Height:  602.9m (converted to OSGM15, Trimble GeoXH 6000) 602.8m (converted to OSGM15, Leica GS15)

Bwlch Grid Reference:  SH 66613 24396

Drop:  147.5m (Trimble GeoXH 6000) 147.6m (Leica GS15) 

Dominance:  19.67%

Pt. 643.2m

Summit Height:  643.2m (converted to OSGM15)

Summit Grid Reference:  SH 64821 22928

Bwlch Height:  621.4m (converted to OSGM15)

Bwlch Grid Reference:  SH 65200 22995

Drop:  21.7m  

Dominance:  3.38%

For details on the bwlch survey of Crib y Rhiw

For further details please consult the Trimble survey spreadsheet click {here}