Monday, 19 October 2015

Mapping Mountains – Hill Reclassifications – 700m Twmpau

Bera Mawr (SH 674 682) - 700m Twmpau reclassified to 700m Sub-Twmpau

There has been a reclassification to the 700m Twmpau (thirty welsh metre prominences and upward) list due to a survey with the Trimble GeoXH 6000, with a subsequent survey having been conducted by Alan Dawson using a Leica RX1250.   The hill is situated in the north-western part of the Carneddau in Eryri, and is positioned south of Llanfairfechan and eastward of Bethesda.

These details are retrospective as the Trimble GeoXH 6000 survey that resulted in the reclassification of this hill from 700m Twmpau to 700m Sub-Twmpau status was conducted on 10th March 2014 on a bright early spring day.

The hill is relatively remote for a Welsh hill and it can be accessed from above Abergwyngregyn to the north, or from the upper parts of Bethesda to the west or from the main Carneddau ridge to its south-east.  Most approaches enable the walker to visit other hills on the way.

The hill is named Bera Mawr and its summit is positioned at SH 674 682.  The hill was listed with c 31m of drop based on a 794m summit spot height and an estimated bwlch height of c 763m.  The area of the bwlch is comprised of relatively short grass and the set-up position of the Trimble for the bwlch survey was given a 0.3m margin of uncertainty for height.

The survey with the Trimble GeoXH 6000 resulted in a 793.6m (converted to OSGM15) summit height with Estimated Accuracies of 15-30cm: 55.22%, this figure is below the average and therefore it would be favourable for this hill to be revisited and another data set gathered for comparison.  The bwlch survey resulted in a 763.9m (converted to OSGM15) height and the normal Estimated Accuracies of 5-15cm: 100.00%.  The survey conducted by Alan Dawson resulted in a 793.69m (converted to OSGM15) summit height at SH 67482 68271.

This now brings the overall total for the hills listed in the 700m Twmpau to 33 and the total for the 700m Sub-Twmpau to 5,  please click {here} to access the list and {here} for its detailed Introduction.

The full details for the hill are:

Cardinal Hill:  Carnedd Llywelyn

Summit Height:  793.7m (converted to OSGM15, Leica RX1250)

Name:  Bera Mawr

OS 1:50,000 map:  115

Summit Grid Reference:  SH 67482 68270

Drop:  29.8m (converted to OSGM15, Leica RX1250 summit and Trimble GeoXH 6000 bwlch)

Gathering data at the summit of Bera Mawr, which resulted in this hill being reclassified from a 700m Twmpau to a 700m Sub-Twmpau

For details on the survey that reclassified this hill from 700m Twmpau to 700m Sub-Twmpau status please click {here}

Myrddyn Phillips (March 2014)

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