Monday, 21 March 2016

Mapping Mountains – Significant Height Revisions – Y Pedwarau

Pt. 483.6m (SH 735 428)

There has been a Significant Height Revision initiated by a survey with the Trimble GeoXH 6000 to a hill that is listed in the Y Pedwarau, with the survey that resulted in this height revision being conducted on 14th March 2016.  The criteria for Pedwar status being all Welsh hills at or above 400m and below 500m in height that have 30m minimum drop.

The hill is currently listed under the point (Pt. 483.6m) notation as it is not named on Ordnance Survey maps, although the hill is positioned next to the small mountain lake of Llyn y Drum.

The hill is situated in the Arenig group of hills and is positioned between the hills of the Moelwynion and the Migneint in north-west Wales, and the survey was conducted on a beautiful sunny, albeit chilly, early spring day.

The hill is positioned above and to the north-west of Llyn Morwynion and can be easily accessed from a track leading to this lake from the B 4391 as it makes its way eastward from Llan Ffestiniog toward its connection with the A 4212, and it is positioned to the south-east of Blaenau Ffestioniog and to the east of Llan Ffestiniog.

When the Y Pedwarau was re-evaluated for Europeaklist publication this hill was listed with a summit height of 486m and its summit position given as the furthest north of four small 480m contour rings that appear on Ordnance Survey 1:25,000 Explorer maps.  The high point of this contour ring is at SH 73542 42903 and the 486m height were taken from a spot height on the Harvey 1:40,000 British Mountain Map to Eryri/Snowdonia.  The position of the listed summit of this hill was moved to SH 73541 42812 after an on-site inspection by Aled Williams.  This summit relocation was later confirmed by the survey conducted with the Trimble GeoXH 6000 with the heights for these two points appearing below:

486m Harvey spot height at SH 73542 42903    Trimbled as 482.686m (converted to OSGM15)

480m OS ring contour at SH 73541 42812    Trimbled as 483.574m (converted to OSGM15)

Therefore this hill’s new summit height is 483.6m (converted to OSGM15) which is 2.4m lower than its previously listed height of 486m and 3.6m higher than the uppermost 480m ring contour that appears on Ordnance Survey 1:25,000 Explorer maps.

The full details for the hill are:

Cardinal Hill:  Graig Goch

Summit Height:  483.6m (converted to OSGM15)

Name:  Pt. 483.6m

OS 1:50,000 map:  124

Summit Grid Reference:  SH 73541 42812

Drop:  34.4m (converted to OSGM15)

Gathering data at the summit of Pt. 483.6m which resulted in this hill's significant height revision

Myrddyn Phillips and Aled Williams (March 2016)

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