Mapping Mountains – Trimble Surveys – Mynydd Hiraethog

18.09.19  Bryn Trillyn (SH 947 590, only bwlch surveyed)

The connecting bwlch of Bryn Trillyn is in utter contrast to its summit.  The latter is heather bound with moor grass and extensive views toward the higher Eryri hills, whilst its bwlch is in a field next to the A543 road at it speeds its way from the outskirts of Pentrefoelas toward Dinbych (Denbigh) in the north-east.

The summit of Bryn Trillyn (SH 947 590)

I’d last visited its summit along with Mark Trengove; watching the sunset from its high point as a thin flash of yellowed light highlighted an otherwise deep and darkening blued sky.

Weather and time of day can dictate many aspects of hill walking, and especially for those related to emotive state, and where the summit had been otherworldly with purpled heather and stillness of the setting sun, my visit to the bwlch consisted of greened fields and an occasional passing vehicle, with middays warmth leaving a contented feeling, but one mainly based on a good job done, as I needed to gather two sets of data, one from either side of the road where the hill to hill traverse descended to a slightly raised strip of tarmac, leaving a low point in each opposing field.

I’d examined the lay of land of this bwlch via the digitised image in a Google car and found a convenient parking place and realised before visiting that a point in the field either side of the road would need surveying.  Therefore, as I left my car I had a quick look on both sides of the road and decided that as the digitised image suggested; two data sets were required.

The Trimble was soon set-up atop my rucksack gathering data on the eastern side of the road.  Its placement was relatively easy to pinpoint as a greened and grassed small and broad ridge descended to the boundary fence, and once data were gathered and stored I closed the equipment down and headed back to the road and the field on its other side.

Gathering data at the bwlch area of Bryn Trillyn

The point to survey on the western side of the road was much tighter and in a dip close to the boundary fence, and as the Trimble beeped away collecting its individual datum points I happily stood back in the sunshine content that this third bwlch survey of the day was nearing completion, but with another six planned I could not linger. 

Gathering data at the second option for the bwlch of Bryn Trillyn

So, once the allotted data were gathered and stored I packed the equipment away and headed back the short distance to my car, checked the map and continued north-east toward the bwlch of Moel Fechan.

LIDAR bwlch image of Bryn Trillyn

Postscript:

Since surveying this hill full LIDAR coverage is now available.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height and positional data that is now freely available for England and Wales.  Consequently the numerical details for this hill have been analysed using this technique, and where appropriate LIDAR has been used in preference to that produced by the Trimble. 

Survey Result:

Bryn Trillyn

Summit Height:  495.6m (LIDAR)

Summit Grid Reference:  SH 94754 59091 (LIDAR) (summit relocation)

Bwlch Height:  446.6m (LIDAR)

Bwlch Grid Reference:  SH 96285 59660 (LIDAR)

Drop:  49.0m (LIDAR)

Dominance:  9.88% (LIDAR)

  

For details on the summit survey of Bryn Trillyn

For further details please consult the Trimble Survey Spreadsheet