Monday, 26 October 2015

Mapping Mountains – Significant Height Revisions – Y Pedwarau

Cerrig y Gordref (SH 929 428)

There has been a Significant Height Revision to a hill that is listed in the Y Pedwarau that was initiated by a survey with the Trimble GeoXH 6000, with these details being retrospective as the survey that resulted in this height revision was conducted on 2nd October 2015.   

The criteria for Pedwar status is all Welsh hills at or above 400m and below 500m in height that have 30m minimum drop.  Whilst the criteria for 400m Sub-Pedwar status is all Welsh hills at or above 400m and below 500m in height that have 20m or more and below 30m of drop.

The name of the hill is Cerrig y Gordref and it is situated in the Arenig group of hills, and is positioned between the towns of Y Bala to the south and Cerrigydrudion to the north north-east.  The hill was surveyed in the company of Aled Williams who had suggested the walk.

The upper section of Cerrig y Gordref is a part of designated open access land and the hill can be easily combined with its neighbours of Y Gesail and Garnedd Fawr, however a more rewarding ascent can be during an extended two car walk, giving the opportunity to visit many of the hills that are situated close to Foel Goch, which is the highest point in this compact group of hills.

The hill was listed in the Y Pedwarau (Europeaklist May 2013) as a 400m Sub-Pedwar with 28m of drop based on the 497m spot height at SH 93066 42836 that appears on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps and the 469m spot height at the bwlch that is positioned at SH 93210 42714 on Ordnance Survey 1:25,000 Explorer maps.  However, the summit area of this hill also has a 495m spot height at SH 92974 42817 that appears on the Ordnance Survey enlarged mapping hosted on the Geograph website.

The high point of the land where the 497m and the 495m spot heights appear on the ground were each surveyed with the Trimble GeoXH 6000 with the following results:

497m spot height:  490.8m (converted to OSGM15) at SH 93066 42834

495m spot height:  494.6m (converted to OSGM15) at SH 92971 42820

The height of the land where the 497m spot height is positioned is significantly lower than Ordnance Survey map data, and this is probably due to a typo on the part of the Ordnance Survey.  Although the height of the land where the 495m spot height is positioned is only 0.4m different to the map height, there is a significant height difference when compared to this hill’s previously listed summit height.

Therefore this hill’s new summit height is 494.6m (converted to OSGM15) which is 2.4m lower than its previously listed height of 497m which was based on the Ordnance Survey  1:50,000 Landranger and 1:25,000 Explorer spot heights which are likely to be a typo, as the land at this point is only 490.8m (converted to OSGM15) high.

The full details for the hill are:

Cardinal Hill:  Foel Goch

Summit Height (New Height):  494.6m (converted to OSGM15)

Name:  Cerrig y Gordref

OS 1:50,000 map:  125

Summit Grid Reference:  SH 92971 42820 
Drop:  26.0m (converted to OSGM15)

Gathering data at the summit of Cerrig y Gordref which resulted in this hill's significant height revision

Myrddyn Phillips and Aled Williams (October 2015)

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