Mapping Mountains – Trimble Surveys – Pumlumon

03.06.18  Fynach Fawr (SN 726 890) and Bryn Gwyn (SN 731 897)

Bryn Gwyn (SN 731 897)

Having visited Allt y Derw (SN 873 834) and Fuches (SN 866 836) earlier in the morning to survey and confirm which hill is higher and their respective status, I now wanted to visit Fynach Fawr and hopefully survey its summit and also clarify its status.

Fynach Fawr is positioned above the western end of Nant y Moch Reservoir and it is swamped in conifer plantation, however baglogs suggest that its summit is relatively easy to reach and an email from Mick Moore had given me a series of ten figure grid references guiding a route to its summit.  Adjacent to Fynach Fawr is a slightly higher map heighted hill named Bryn Gwyn, and recent baglogs mention that its summit is now clear of conifer plantation, I hoped to visit both and bring back data from each summit and the connecting bwlch.

It seemed a long drive from the small community of Ponterwyd toward Nant y Moch and then around its southern and western shore to the forest track that gives access to these two hills.  The previous evening I had followed a Google car on my laptop up this forest track and noted a large parking area where Mick’s directions then accessed a forest ride.

I set off walking just before midday and used the Trimble as a hand-held device checking on the ten figure grid references Mick had sent me, a gravelled section led down to a grassed forest ride where another set off upward on the right, I followed the latter but found going easier within the conifer plantation due to a number of wind-blown felled trees that obstructed easy access.

The route in to the trees and to the top of Fynach Fawr turns right at the end of the gravel

The forest ride leading to the hill's northern ridge proved to be an obstacle course

This forest ride led to the summit ridge that descends northward from the top of Fynach Fawr, and although the forest ride continued in the same westerly direction, it was easy to spot where the southerly route leading to this hill’s high point was.

Following this ridge also proved problematic due to wind-blown and felled conifers, and I found the going easier on the way down when I kept slightly below the ridge, however on the way up I negotiated a route over and past a number of wind-blown and felled trees until I found my way to what looked like the high point of the hill, I checked the grid reference from the Trimble and it matched that produced by Mick to within ten metres, I was at the point where Mick had determined was the summit of this hill.

Over recent times the status of Fynach Fawr had altered due to details produced by LIDAR analysis, and this was then questioned as the summit position produced by LIDAR did not match that from Mick’s on-site visit.  Before trying to gather data from the point where I also judged the summit to be, I wanted to investigate further in to the trees and headed off to where LIDAR gives the position of the high point, and all I found was ground that continued downhill.

I judged the summit of Fynach Fawr to be under one of the conifers and placed the Trimble atop my rucksack in the forest ride which was beside this point and 4 metres east of it and measured an offset between each.  I then created the file in the Trimble and waited for it to achieve its 0.1m accuracy level.

Experience has shown that waiting for this accuracy level to be attained when the Trimble is placed on a forested summit can be a long process and today was one of the longest!

I waited a long time, occasionally checking on the accuracy level and also investigating further in to the plantation, I spent much of this time sitting on a tree stump listening to bird song that eventually merged in to my mind.  Dappled light sped down from a blue sky above and a slight breeze blew bearded moss that delicately hung from conifers in front of me.  Occasionally I stood, but mainly I sat, and waited.  A flash of colour highlighted an otherwise meditative state that I had reached when a Jay blew between the trees, otherwise I just waited.

The intricacies of bearded moss

The tree stump where I sat for 80 minutes waiting for the Trimble to attain its accuracy level and gather data

After 40 minutes I turned the Trimble off and re-activated it as the accuracy level had not been attained, then started another long wait, after about 80 minutes I finally pressed ‘Log’ and retired to my tree stump and waited a further 12 minutes for data to be stored.

It had been a long wait for the Trimble to gather data, but with this done I could now retrace my route back out of the conifers down to my car and toward the felled forestry at the top of Bryn Gwyn.

The Trimble set-up position at the summit of Fynach Fawr

Forested summits are not my favourite and neither are they my preferred option for an enjoyable day’s hill walking, however the mind of a hill bagger works in mysterious ways and they are all too easily tackled to get that all important tick against their top.  Felled forestry can also be wearisome as summits can resemble an assault course and Bryn Gwyn looked as if it was going to treat me to a dire few minutes, but I found the ploughed runnels of a vehicle track that led up the southern slopes of this hill and rounded to the north where it became a green runnel almost resembling a path, this miraculously led to within a few metres of the hills’ summit.

Fynach Fawr from Bryn Gwyn

I took data from two points at the summit area of Bryn Gwyn, during each I sat on conveniently placed tree stumps and savoured the warmth of the sun and soaked myself in the view.

Gathering data at the summit of Bryn Gwyn

Just one survey remained and that was the connecting bwlch between these two hills, and after packing the Trimble away I retraced my inward route down from the summit of Bryn Gwyn to the bwlch of Fynach Fawr which was placed beside the forestry track a few metres from where I had parked my car.

Gathering data at the bwlch of Fynach Fawr which proved conveniently placed for the walk back to my car!

Once bwlch data were gathered and stored I headed to my car, got changed, enjoyed the sun, had a bite to eat and drove down the forest track to the narrow road and headed west toward Tal-y-bont, and then continued to Llanidloes where I called to see two good friends; Darrin and Lisa, and spent a very enjoyable late afternoon and evening in their company.

Survey Result:

Fynach Fawr

Summit Height:  462.5m (converted to OSGM15)

Summit Grid Reference:  SN 72685 89095

Bwlch Height:  432.5m (LIDAR)

Bwlch Grid Reference:  SN 72911 89413 (LIDAR)

Drop:  30.0m (Trimble summit and LIDAR bwlch) (400m Sub-Pedwar reclassified to Pedwar)

Dominance:  6.49% (Trimble summit and LIDAR bwlch)

Bryn Gwyn

Summit Height:  471.6m (converted to OSGM15)

Summit Grid Reference:  SN 73118 89750

Bwlch Height:  420.0m (LIDAR)

Bwlch Grid Reference:  SN 72846 90037 (LIDAR)

Drop:  51.6m (Trimble summit and LIDAR bwlch)

Dominance:  10.94% (Trimble summit and LIDAR  bwlch)

For further details please consult the Trimble Survey Spreadsheet