Wednesday, 3 May 2017

Mapping Mountains – Significant Height Revisions – Y Trichant

Moel Llaethbwlch (SJ 113 167)

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 Trichantwith the survey that resulted in this height revision conducted on the 6th April 2017.

The criteria for the listing that this height revision affects are:

Y Trichant - Welsh hills at and above 300m and below 400m in height that have 30m minimum drop.  The list is authored by Myrddyn Phillips and the Introduction to the list and its re-naming was published on Mapping Mountains on the 13th May 2017.

The name of the hill is Moel Llaethbwlch and it is situated in the Y Berwyn range of hills which are in the south-east part of North Wales, and the hill is positioned between the town of Llanfyllyn to the north-east and the village of Meifod to the south-east.

As the summit of the hill is not a part of designated open access land permission to visit should be sought, with the nearest public footpaths contouring round the hill’s northern lower slopes and also its lower southern slopes.

Prior to the survey with the Trimble GeoXH 6000 the height of the hill was estimated as c 370m based on the small uppermost 370m ring contour on Ordnance Survey 1:25,000 Explorer maps, and to my knowledge no spot height has ever appeared on an Ordnance Survey map for this hill.

The 372.1m (converted to OSGM15) height produced by the Trimble GeoXH 6000 is not a dramatic increase from the previously estimated summit height of c 370m, 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, or a previous estimated summit height based on contour interpolation.  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 in favour of the 1:50,000 map for detailing these revisions.

The summit of this hill is easily identified and consists of closely cropped grass at the top of a field used for grazing.  Although the immediate summit area is relatively flat it is encircled by what looks like the remains of a small hill fort, although I have found no evidence to support this.

Therefore this hill’s new summit height is 372.1m (converted to OSGM15) which is 2.1m higher than its previously estimated height of c 370m and also 2.1m higher than its 370m uppermost ring contour on Ordnance Survey maps.

The full details for the hill are:

Cardinal Hill:  Moel y Fronllwyd

Summit Height (New Height):  372.1m (converted to OSGM15)

Name:  Moel Llaethbwlch

OS 1:50,000 map:  125

Summit Grid Reference:  SJ 11335 16724
Drop:  43.3m (converted to OSGM15)

The Trimble GeoXH 6000 gathering data at the summit of Moel Llaethbwlch (SJ 113 167)  which resulted in this hill's significant height revision

Myrddyn Phillips (May 2017)

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