Monday, 21 March 2016

Mapping Mountains – Significant Height Revisions – Y Pedwarau


Pt. 483.6m (SH 735 428)

This is the twenty seventh post under the heading of Significant Height Revisions, and the Trimble survey that resulted in this height revision was conducted on 14th March 2016.

The twenty seventh major height revision initiated from a survey with the Trimble GeoXH 6000 was conducted in the hills between the Moelwynion and the Migneint in north-west Wales, on a beautiful sunny, albeit chilly, early spring day.

The hill is situated above and to the north-west of Llyn Morwynion and can easily be 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.  The hill is positioned to the south-east of Blaenau Ffestioniog and to the east of Llan Ffestiniog.

The hill is not named on Ordnance Survey maps, although it appears next to the small mountain lake of Llyn y Drum, because of this its name currently follows the point (Pt.) notation; Pt. 483.6m.

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 maps.  The high point of this contour ring is at SH 73542 42903 and the 486m height 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 upon a visual inspection by Aled Williams.  This was later confirmed by a Trimble survey 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 current Ordnance Survey 1:25,000 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


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

For details on the survey that significantly revised the summit height of this hill please click {here}

Myrddyn Phillips and Aled Williams (March 2016)




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