Friday, 14 August 2015

Mapping Mountains – Significant Height Revisions – Y Trichant and Y Trechol - The Dominant Hills of Wales

Coed y Gaer (SO 004 843)

There has been a Significant Height Revision initiated by a survey with the Trimble GeoXH 6000 to the listing of Y Trichant and Y Trechol - The Dominant Hills of Wales, with the following details being retrospective as the survey that resulted in this height revision was conducted on 9th February 2014.  The hill is listed as a Lesser Dominant as well as a Trichant, with the latter being the 300m height band of Twmpau (thirty welsh metre prominences and upward) hills.

The criteria for the two listings that this height revision affects are:

Y Trichant - these are the Welsh hills at or above 300m and below 400m in height that have a minimum drop of 30m. 

Y Trechol - The Dominant Hills of Wales - these are the Welsh P30 hills whose prominence  equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those addition Welsh P30 hills whose prominence is 33% or more and below 50% of their absolute height.

The name of the hill is Coed y Gaer and it is situated in the Pegwn Mawr range of hills to the east of Llanidloes, and the survey was conducted in the company of Mark Trengove on a particularly wet and cold day.  The hill can be accessed from a minor lane to the south of its summit; and it overlooks the A470 and the Afon Hafren (River Severn) which are to its north-west.

The height given the hill on current Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps is 362m, with the height resulting from the survey with the Trimble being 359.9m (converted to OSGM15).  This is not a dramatic height revision but it does come within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revision applies to any listed hill whose Ordnance Survey summit spot height has a 2m or more discrepancy when compared to the surveyed height produced by the Trimble GeoXH 6000, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble.  As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 map is being prioritised for detailing these revisions.

The full details for the hill are:

Cardinal Hill:  Pegwn Mawr

Summit Height (New Height):  359.9m (converted to OSGM15)

Name:  Coed y Gaer

OS 1:50,000 map:  136

Summit Grid Reference:  SO 00488 84392
Drop:  121.7m (converted to OSGM15)

Dominance:  33.80%

Gathering data with the Trimble GeoXH 6000 from the summit of Coed y Gaer

Myrddyn Phillips (August 2015)

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