Mapping Mountains – Significant Height Revisions – Y Pedwarau

Craig y Garreg Lwyd (SH 730 427)  

There has been a Significant Height Revision initiated by a survey with the Trimble GeoXH 6000 to the listing of the Y Pedwarau, and which was later confirmed by a survey with a Leica GS15, with these details being retrospective as the survey that resulted in this height revision was conducted on 14^th March 2016 in good, bright conditions, albeit with a chilling easterly breeze blowing .

The criteria for the listing that this height revision affects are:

Y Pedwarau - Welsh hills at and above 400m and below 500m in height that have 30m minimum drop.

400m Sub- Pedwarau - Welsh hills at and above 400m and below 500m in height that have 20m or more and below 30m of drop.

The hill is named Craig y Garreg Lwyd and it is situated in the Arenig group of hills between the Moelwynion to the west and the wilds of Y Migneint to the east, with these hills situated in north-west Wales. 

The hill is positioned above and to the north-west of Llyn Morwynion and can be easily accessed from a number of tracks that lead in from its south, south-west and south-east, with each track starting from the B 4391 road as it makes its way eastward from Llan Ffestiniog toward its connection with the A 4212, and the hill is positioned to the south-east of Blaenau Ffestioniog and to the east of Llan Ffestiniog.

Prior to the survey with the Trimble GeoXH 6000 Craig y Garreg Lwyd was listed as a Pedwar with 35m of drop based on the 478m and 443m spot heights that appear on the summit and bwlch respectively on the Ordnance Survey enlarged mapping hosted on the Geograph website.

The survey with the Trimble GeoXH 6000 produced a 473.4m (converted to OSGM15) summit height and a 443.5m (converted to OSGM15) bwlch height and as the former was significantly lower than the 478m summit spot height on the Ordnance Survey enlarged mapping hosted on the Geograph website, all available online Ordnance Survey Six-Inch maps on the National Library of Scotland website, the Historical Ordnance Survey maps on the Sabre Maps website and the Ordnance Survey Vector mapping were then checked and there is no evidence of a previous imperial height or another metric height for this hill.  Therefore, it seems the 478m spot height is the only height adjoined to the summit of this hill on publicly available maps.

Craig y Garreg Lwyd was subsequently surveyed by John Barnard and Graham Jackson using a Leica GS15 resulting in a 473.8m (converted to OSGM15) summit height and a 443.6m (converted to OSGM15) bwlch height.

Therefore this hill’s new summit height is 473.8m (converted to OSGM15) which is 4.2m lower than its previously listed height of 478m which appears on the Ordnance Survey enlarged mapping hosted on the Geograph website.

The full details for the hill are:

Cardinal Hill:  Graig Goch

Summit Height:  473.8m (converted to OSGM15)

Name:  Craig y Garreg Lwyd

OS 1:50,000 map:  124

Summit Grid Reference:  SH 73047 42746

Drop:  30.2m

Gathering data at the summit of Craig y Garreg Lwyd (SH 730 427) which resulted in this hill's significant height revision

For details on the survey that significantly revised the summit height of this hill

Myrddyn Phillips and Aled Williams (March 2016)