Thursday, 3 March 2016

Mapping Mountains – Trimble Surveys – Moel Hebog


23.02.16  Moelfre (SH 561 376) and Moelfre (SH 558 375)  

The lower easterly summit of Moelfre (SH 561 376) with the high Moelwynion beyond

With a forecast of early morning frost and dry conditions I headed toward Porthmadog with a plan to tidy up a few past surveys.  I hoped to visit four places in all, with some surveys involving summits and others just bylchau.  With the first planned survey taking in the two summits of Moelfre, a hill whose name was found through local enquiry with Aled Williams; a native of Porthmadog.  The summit position of this hill has changed in recent times due to a 74m spot height appearing on its westerly top on the Ordnance Survey enlarged map on the Geograph website.  The top that has been replaced has a 72m spot height on it and lies just to the east and the land where its summit is situated is named Cae Bach on the Tithe map, although the hill taking in this easterly summit is still known locally as a part of Morlfre, both summits needed Trimbling.

I parked at the bwlch on the grass verge beside a ladder stile and gate giving access to a track heading toward a Lama Centre, one or two of these animals could be seen munching away as I gathered all my stuff and walked down the road to a gate which gave access on to a field.

Plodding up the field the sun shone bright highlighting the frost still evident on the higher Eryri peaks.  I aimed for the easterly summit first and carefully clambered over a wall as the summit came in to view.  This comprises grass beside large clumps of gorse.  Having set the Trimble up I stood back and waited for it to gather its allotted five minutes of data.

Gathering data at the easterly summit of Moelfre with the higher westerly summit of Moelfre in the background

As I packed the Trimble away there was spring warmth in the air and the sea sparkled toward the west.  Backtracking over the wall I descended to the connecting bwlch and again gathered five minutes of data.  When on my own I try and survey everything that I can, and this connecting bwlch is an example of this philosophy as the easterly summit of Moelfre stands an outside chance of becoming a Sub-Twmpau.  With an expensive bit of surveying kit that gives accurate results I want to produce as much data as I can, and that means bylchau such as this should be surveyed.

Beyond the bwlch was the 74m spot heighted summit of Moelfre, it was only a short walk to the high point, which is immersed just inside a large growth of gorse.  Outside the gorse was another high point which was visually lower, but as the human eye can be rather deceptive where judging height is concerned I decided to survey both points.

Gathering data at the westerly summit of Moelfre

A lovely place to spend a couple of hours on a winter's morning

Once data were gathered I headed down to the gate and walked back beside the road to my car and the connecting bwlch for the higher of the two summits.  When I had first arrived I’d had a quick look at the lay of land at this bwlch and thought it hard to judge where the critical point lay, but when I walked back to it, the valley to valley traverse was easily followed to its high point, and the hill to hill connection likewise.  However, the critical bwlch is positioned beside a solid stone wall which has a ladder stile giving access to a track.  I positioned the Trimble on top of my rucksack which was sitting on top of the wall and measured a 1.78m offset between the internal antenna and the ground.

Gathering data at the critical bwlch of the higher of the two summits of Moelfre

Once five minutes of data were gathered I packed the Trimble away and drove back to Porthmadog and continued on the A 497 toward the bwlch of Moel y Gadair (SH 521 391), which is positioned to the south-west of the small community of Pentrefelin.

I’d surveyed the summit of Moel y Gadair in June of last year and had fun trying to assess where its critical bwlch was positioned.  I know knew where the Trimble should be set up and also suspected that the hill could be deleted from the ranks of P30s.  


Survey Result:



Summit Height:  73.3m (converted to OSGM15, and lower summit confirmed)

Summit Grid Reference:  SH 56181 37683

Bwlch Height:  54.8m (converted to OSGM15)

Bwlch Grid Reference:  SH 56018 37592

Drop:  18.5m (non 30–99m Sub-Twmpau status confirmed)

Dominance:  25.26%





Summit Height:  74.1m (converted to OSGM15, and higher summit confirmed)

Summit Grid Reference:  SH 55830 37553

Bwlch Height:  37.8m (converted to OSGM15)

Bwlch Grid Reference:  SH 55625 37768

Drop:  36.3m




For further details please consult the Trimble survey spreadsheet click {here}



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