Tuesday, 18 July 2017

Mapping Mountains – Hill Reclassifications – 700m Twmpau

Craig Eigiau (SH 713 654) – 700m Sub-Twmpau addition

There has been an addition to the Twmpau (thirty welsh metre prominences and upward)  list due to a survey with the Trimble GeoXH 6000, and a subsequent survey by Alan Dawson with the Leica RX1250, with this hill being included in the 700m Sub-Twmpau.  Accompanying all the 100m height band of hills within the Twmpau are sub lists with the one attached to this list being entitled the 700m Sub-Twmpau

The criteria for 700m Twmpau status is all Welsh hills at or above 700m and below 800m in height with 30m minimum drop, the criteria for 700m Sub-Twmpau status is all Welsh hills at or above 700m and below 800m in height with 20m or more and below 30m of drop.  Details to this height band of the Twmpau were published on the Mapping Mountains site on 15th April 2015.

Prior to the survey with the Trimble GeoXH 6000 the summit of this hill had been analysed with LIDAR data by Aled Williams, resulting in a 733.9m height, and it had remained listed as an Uchaf with an estimated c 19m of drop based on the 735m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger map and the 1:25,000 Explorer map, with an estimated bwlch height of c 716m based on bwlch contouring between 710m – 720m. 

The name of the hill is Craig Eigiau and it is situated in the Carneddau group of hills and is placed in the Region of North Wales (Region A, Sub-Region A1) with its Cardinal Hill being Carnedd Llywelyn (SH 683 643).  The hill is positioned between two reservoirs; Melynllyn to its west and Llyn Eigiau to its east, with the small community of Tal-y-bont to the north-east of the hill, and it can be visited via its northern ridge which can be gained from a track leaving the high car park close to Llyn Eigiau, however it is more rewarding to combine this hill in a longer walk with a number of its higher neighbours.

The survey with the Trimble produced a summit height of 734.7m (converted to OSGM15) at SH 71314 65425 and a bwlch height of 713.9m (converted to OSGM15) at SH 71185 65473, with these values giving this hill 20.8m of drop, with the details from the Leica RX1250 survey conducted by Alan Dawson being 735.0m (converted to OSGM15) summit height at SH 71315 65425 and 714.0m (converted to OSGM15) bwlch height at SH 71191 65460, with these values giving this hill 20.9m of drop, which is sufficient for its addition to 700m Sub-Twmpau status.  This now revises the total in the 700m Twmpau which will be updated accordingly.

The full details for the hill are:

Cardinal Hill:  Carnedd Llywelyn

Summit Height:  735.0m (converted to OSGM15, Leica RX1250)

Name:  Craig Eigiau

OS 1:50,000 map:  115

Summit Grid Reference:  SH 71315 65425 
Drop:  20.9m (converted to OSGM15, Leica RX1250)

The overall total for the 700m Twmpau remains at 32 hills with two reclassifications to 700m Sub-Twmpau status since publication of this list on the Mapping Mountains site on 15th April 2015.

The overall total for the 700m Sub-Twmpau is now 7 hills with two reclassifications from 700m Twmpau status and one addition since publication of the list on the Mapping Mountains site on 15th April 2015.

The list of 700m Twmpau is available from Mapping Mountains (April 2015) with all subsequent changes detailed in the 700m Twmpau – Hill Reclassifications on the Mapping Mountains site.

The Trimble GeoXH 6000 gathering data at the summit of Craig Eigiau

Myrddyn Phillips (July 2017)

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