Mapping Mountains – Hill Reclassifications – 700m Twmpau

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

There has been a deletion to the listing of the 700m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips and a subsequent Leica RX1250 survey conducted by Alan Dawson. 

Bera Mawr (SH 674 682)

The criteria for the list that this reclassification applies to are:

700m Twmpau - Welsh hills at or above 700m and below 800m in height with 30m minimum drop, with an accompanying sub list entitled the 700m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 700m and below 800m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.  The list is authored by Myrddyn Phillips and is available to download in Google Doc format from Mapping Mountains.

700m Twmpau by Myrddyn Phillips

The name the hill is listed by is Bera Mawr and it is adjoined to the Carnedd Llywelyn group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with the A55 road to to its north and the A5 road towards its south-west, and has the town of Llanfairfechan towards the north.

When the list that became known as the 700m Twmpau was first compiled, this hill was included in the main list with an estimated c 31m of drop, based on the 794m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and an estimated c 763m bwlch height, based on interpolation of 10m contouring between 760m – 770m.

Extract from the Ordnance Survey 1:25,000 Explorer map

However, it was not until the Trimble GeoXH 6000 survey that the details for this hill could be accurately re-assessed.  This survey resulted in a 793.6m summit height and a 763.9m bwlch height, with these values giving this hill 29.7m of drop.  The hill has subsequently been surveyed by Alan Dawson using the Leica RX1250, with the resulting summit height being prioritised for the listed values of this hill.

The Trimble GeoXH 6000 gathering data at the summit of Bera Mawr

Therefore, the reclassification of this hill to 700m Sub-Twmpau status is due to a Trimble GeoXH 6000 survey with a subsequent Leica RX1250 summit survey being prioritised for listing purposes, resulting in a 793.7m summit height and a 763.9m bwlch height, with these values giving this hill 29.8m of drop, with is insufficient for it to be classified as a 700m Twmpau. 

The full details for the hill are:

Group:  Carnedd Llywelyn

Name:  Bera Mawr

OS 1:50,000 map:  115

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

Summit Grid Reference:  SH 67482 68271 (Leica RX1250)

Bwlch Height:  763.9m (converted to OSGM15, Trimble GeoXH 6000)

Bwlch Grid Reference:  SH 67513 68149 (Trimble GeoXH 6000)

Drop:  29.8m (Leica RX1250 summit and Trimble GeoXH 6000 bwlch)

Myrddyn Phillips (March 2014)