Mapping Mountains – Trimble Surveys – Arenig

07.02.20  Arenig Fach (SH 820 415), only bwlch surveyed

Arenig Fach stands as a great lump of wild rock and wind-blown heathered moor.  No ascent is particularly easy, although the hill does afford solitude and expansive views.  I’d surveyed its summit in November 2016 during Steve Smith’s celebratory completion of the Nuttalls.  On that day the summit was bleakly chilled and wet.  Today for its bwlch survey the weather forecast gave settled conditions, albeit with the breeze increasing in strength during the early afternoon, as it was just before 10.00am when I pulled up and parked beside the A4212 this did not concern me.

Arenig Fach (SH 820 415)

Prior to my visit the position and height of this bwlch had been determined by LIDAR analysis conducted by Aled Williams, and it was the ten figure LIDAR grid reference that I was now reliant upon for Trimble placement.

I had inspected the land beside the A road in a Google car on my laptop and the southern roadside verge had intermittent small conifer trees on it, I hoped that its critical point would not prove to be either under or beside one of these as this may interrupt signals received by the Trimble.

The bwlch of Arenig Fach

It was only a short walk on the road to where the bwlch of Arenig Fach is situated and with the Trimble used as a hand-held device I quickly zeroed in to its critical point, which was beside one lone conifer tree.  The road at this point had been slightly raised above its moorland surrounds and if not for LIDAR, the positioning of the critical point of this bwlch may have taken an inordinate amount of time to assess.

The Trimble was soon positioned on top of my rucksack, which acts as an improvised tripod, giving it elevation above its immediate surrounds, and once the 0.1m accuracy level was attained before data should be logged, I pressed ‘Log’ and retreated across the other side of the road and waited patiently whilst six minutes of data were gathered and stored.

The Trimble set-up position at the bwlch of Arenig Fach

During this time I counted the cars that passed, three headed west toward Trawsfynydd whilst eight headed east toward Y Bala.  It wasn’t a particularly busy stretch of road on this day for this part of Wales.

Once data were gathered and stored I pressed ‘Done’, closed the equipment down, packed it away and walked the short distance back to my car and headed toward the third of four planned bwlch surveys for the day; the next survey being the bwch that connects to Carnedd Iago (SH 782 406).

Survey Result:

Arenig Fach

Summit Height:  688.9m (converted to OSGM15, from previous Trimble GeoXH 6000 survey)

Summit Grid Reference:  SH 82020 41583

Bwlch Height:  390.6m (converted to OSGM15)

Bwlch Grid Reference:  SH 78593 38716

Drop:  298.3m

Dominance:  43.30%

  

For details on the summit survey of this hill

For further details please consult the Trimble Survey Spreadsheet