Thursday, 22 October 2015

Mapping Mountains – Significant Height Revisions – Y Trichant

Cefn Llwydallt (SO 074 409)

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 Trichant, with the following details being retrospective as the survey that resulted in this height revision was conducted on the 29th September 2015.  The Y Trichant comprises all Welsh hills at and above 300m and below 400m in height that have 30m minimum drop, with the Introduction to this list and its re-naming being published on Mapping Mountains.

The name of the hill is Cefn Llwydallt and it is situated in the south-eastern lands of Mynydd Epynt, and is positioned above the small communities of Erwyd (Erwood) to the north-east, Capel Uchaf (Upper Chapel) to the west and Llaneglwys to the south-west.

Access to the hill is relatively easy as the summit is situated on open access land and there is a minor road to the north-west next to where the bwlch of the hill is positioned.  Alternate routes to the summit can use public footpaths from the north-east, east and south that head toward the open access land, with the summit of the hill positioned amongst small gorse bushes.

The hill was surveyed in the afternoon toward the end of a ridge walk that took in a number of hills from Cefn Clawdd (SO 043 403) heading eastward, and prior to the survey with the Trimble GeoXH 6000 the hill was listed as being 378m high based on the old 1,240ft (378.0m) imperial height given the hill on the Ordnance Survey Six-Inch map.

The survey result for the summit produced by the Trimble GeoXH 6000 is 380.7m (converted to OSGM15).  This is not a dramatic height revision when compared to its old listed height, 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 survey result 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.

Therefore this hill’s new summit height is 380.7m (converted to OSGM15) which is 2.7m higher than the previously listed height of 378m which was based on the old imperial 1,240ft height taken from the Ordnance Survey Six-Inch map.

The full details for the hill are:

Cardinal Hill:  Clepyn Melyn

Summit Height (New Height):  380.7m (converted to OSGM15)

Name:  Cefn Llwydallt

OS 1:50,000 map:  147, 160

Summit Grid Reference:  SO 07422 40950 
Drop:  41.0m (converted to OSGM15)

Gathering data from the summit of Cefn Llwydallt which resulted in this hill's significant height revision

Myrddyn Phillips (October 2015)

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