Saturday, 13 June 2020

Mapping Mountains – Trimble Surveys – Moelwynion

07.02.20  Moelwyn Mawr (SH 658 448), only bwlch surveyed

The last of four bwlch surveys of the day was at the top of Bwlch y Gorddinan, which in English is known as the Crimea Pass.  This bwlch is placed at the top of the A470 road as it heads north-eastward from Blaenau Ffestiniog toward the A5 road and Betws-y-coed, and it connects to Moelwyn Mawr, which is one of the highest hills in the Moelwynion range and towers above the near town of Blaenau Ffestiniog.

Moelwyn Mawr (SH 658 448)

I hadn’t surveyed the summit of Moelwyn Mawr, although I had visited on 19 occasions.  However, I had driven over this bwlch many times, usually when heading north, but other times whilst visiting the hills connecting with Manod Mawr to the east or those connecting with Allt Fawr to the west, until today I hadn’t had the opportunity to survey it.

Prior to my visit I looked at the lay of land from the convenience of a digitised image via a Google car on my laptop and also examined the 5m contouring on the OS Maps website.  The latter implies the critical point of the bwlch is on the A road, whilst the former leaves the impression that it is positioned close to where a track leaves the road via a gate.

The bwlch of Moelwyn Mawr

By the time I arrived and parked at the gate entrance the breeze from early morning had increased in strength, but not so much as to hinder any survey.  Having spent five minutes examining the lay of land I repositioned my car nearer the gate entrance and again looked at where the stream valley came up from the confines of the Afon Gorddinan to the north and crossed the track close to the gate entrance and headed down beside the A470.  The only thing to pinpoint was its exact critical point.  This could easily be positioned in a small fenced compound beside the track.

This small patch of land consisted of scrub grass and was even in nature implying that the critical point was beside the outer fence where a number of fence posts gave the opportune convenience to place the Trimble on top, and by doing so creating a high improvised tripod with elevation for the equipment above its immediate surrounds.

Gathering data at the bwlch of Moelwyn Mawr

As I chose the fence post for Trimble placement, measured the offset between its internal antenna and the ground below, and set the equipment to gather data I looked out on the surrounding hills; Moel Siabod looked inviting as a distant bulk of a hill with a slither of road snaking its way toward it, whilst the nearer Allt Fawr shot skyward bathed in early afternoon light.  Whilst to my east lay Moel Farlwyd, which I knew had been surveyed by John Barnard and Graham Jackson in the last two days to confirm its impending Hump status.  I was tempted to survey this hill prior to their visit, but thought I’d leave it to the professionals!

Moel Siabod

Allt Fawr

As the Trimble beeped away gathering its individual datum points I stood on the opposite side of the road and waited for the allotted six minutes of data to be stored.  Once data collection was complete I closed the equipment down, packed it away and headed down from the bwlch to a convenient lay-by to change and continue toward Nantlle for the weekend’s festivities.

Survey Result:

Moelwyn Mawr

Summit Height:  770m (triangulation pillar)

Summit Grid Reference:  SH 65821 44859 (triangulation pillar)

Bwlch Height:  384.5m (converted to OSGM15)

Bwlch Grid Reference:  SH 70000 48660

Drop:  385m (triangulation pillar summit and Trimble GeoXH 6000 bwlch)

Dominance:  50.06% (triangulation pillar summit and Trimble GeoXH 6000 bwlch) (Dominant status confirmed)


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