Saturday, 26 September 2015

Mapping Mountains – Significant Height Revisions – Y Pedwarau


Bryn Serth (SO 147 109)  

This is the eighteenth post under the heading of Significant Height Revisions, and the following details are retrospective as the Trimble survey that resulted in this height revision was conducted on 12th August 2015.

The eighteenth major height revision initiated from a survey with the Trimble GeoXH 6000 was conducted in the hills of the Cymoedd in south Wales, during a walk in the company of Mark Trengove who had suggested the survey.

The hill is situated on the northern outskirts of Tredegar at the head of the Cwm Sirhywi (Sirhowey Valley) and it can be easily accessed from a car park beside the busy A4047 which is positioned south-east of the summit.  This car park also gives access to the Aneurin Bevan Memorial Stones; these consist of four monoliths and are set against the landscape of Ebbw Vale, Tredegar and Rhymney which form the constituencies which Aneurin Bevan represented during his years in Westminster.

The name of the hill is Bryn Serth and until the Trimble survey it was listed as a Pedwar with its summit height estimated as c 410m based on a small uppermost 410m ring contour that appears on current Ordnance Survey maps.  However, this point is not the high point of the hill as land approximately 100 metres further north was surveyed by the Trimble as being 2.0m higher than the position where the uppermost contour ring appears on the ground.

The two points surveyed with the Trimble GeoXH 6000 gave results that are significantly lower than current Ordnance Survey map data, these results are:


Northern summit:  403.927m (converted to OSGM15) at SO 14794 10908

Southern summit:  401.890m (converted to OSGM15) at SO 14782 10809


It is the southern summit where the small 410m ring contour appears on current Ordnance Survey maps.

Since processing the data sets from this survey Aled has scrutinised on-line mapping and found that the Ordnance Survey Six Inch map has a 1,327ft (404.47m) height on the area of the summit and a 1,242.5ft (378.71m) height on the area of the bwlch.  These Six Inch map values give Bryn Serth a drop of 25.76m which is comparable to the Trimble result.

Therefore using the Trimble result this hill’s new summit height is 403.9m (converted to OSGM15) which is 6.1m lower than its previously estimated height of c 410m and 6.1m lower than its uppermost ring contour on current Ordnance Survey maps.


The full details for the hill are:

Cardinal Hill:  Cefn Manmoel

Summit Height (New Height):  403.9m (converted to OSGM15)

Name:  Bryn Serth

OS 1:50,000 map:  161

Summit Grid Reference:  SO 147 109

Drop:  25.4m


Gathering data from the summit of Bryn Serth 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 (August 2015)


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