Sunday, 8 December 2019

Mapping Mountains – Trimble Surveys – Aran

13.09.19  Aran Fawddwy (SH 862 223), only bwlch surveyed

Aran Fawddwy is the highest hill in Britain south of Yr Wyddfa and as such it dominates the land around it.  The view from its summit is extensive with ridge upon ridge of diminishing hills to its east and the higher Eryri hills far off to its north.  I’d visited its summit 19 times but had never visited its bwlch, although I had driven over it on many occasions.  This bwlch is positioned beside the A494 road as it makes its way from Dolgellau in the south-west to Y Bala in the north-east.

Aran Fawddwy (SH 862 223)

The bwlch is unassuming, as many bylchau are.  Outside of the many vehicles that pass over it on a daily basis I wonder if anyone has ever visited it because of what it is.  I suspect not.

Prior to my visit Aled Williams had LIDARed the bwlch and afterward I did likewise.  I also drove a Google car in the vicinity of the bwlch to compare the placement of the bwlch via LIDAR to the lay of land via a digitised image, and found by parking at the entrance to Pant Gwyn on the western side of the road it would enable me to position the car directly over the position of the bwlch according to LIDAR.

LIDAR bwlch image for Aran Fawddwy

I arrived mid-afternoon and manoeuvred my car in to position leaving sufficient space for any vehicle driving in or out of Pant Gwyn, and importantly with the front of the car safely positioned off of the main road.

The car in place with the Trimble on its roof

Also crossing this point is the disused railway line that connected Dolgellau to Y Bala, its course can easily be seen either side of the road and before setting the Trimble up to gather data I wanted to investigate the land beside the road.  My conclusion is that the building of the rail line and road has increased the height of this bwlch from its natural point, but determining the natural height and its position is now probably impossible, therefore I concentrated on the LIDAR position and aligning the Trimble with it as it was placed on top of my car’s roof. 

The set-up position beside the grass verge next to the drive leading to Pant Gwyn

Once the offset between the Trimble’s internal antenna and the ground below was measured and noted, I created the file and waited for the 0.1m accuracy level to be attained and then pressed ‘Log’ and waited for the allotted data to be gathered and stored.

Gathering data at the bwlch of Aran Fawddwy

During this I stood back and watched the steady hum of cars hurtle past whilst enjoying the afternoon sunshine.  After the Trimble was closed down a vehicle appeared from Pant Gwyn, I went over to say hello and explain what I was doing, and the occupant said she did wonder.  We chatted for a number of minutes and she explained that her family farm from Rhyd-y-main and I wondered if I had made place-name enquires with her husband during the extensive enquiries with local famers when I covered the Aran range.

After I packed the Trimble and the surveying steps away I waved my goodbye’s and headed toward Y Bala and the B4391 road crossing the Y Berwyn for the last survey of the day.

Survey Result:

Aran Fawddwy

Summit Height:  905.6m (Leica RX1250)

Summit Grid Reference:  SH 86270 22386 (Leica RX1250)

Bwlch Height:  232.7m (converted to OSGM15)

Bwlch Grid Reference:  SH 85050 26799

Drop:  672.9m

Dominance:  74.30%


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