Wednesday, 3 May 2017

Mapping Mountains – Significant Height Revisions – Y Trichant

Moel Llaethbwlch (SJ 113 167)

This is the thirty eighth post under the heading of Significant Height Revisions, with the Trimble survey that resulted in this height revision being conducted on the 6th April 2017.

The thirty eighth major height revision initiated from a survey with the Trimble GeoXH 6000 was conducted in the Y Berwyn range of hills in the south-east part of North Wales, between the town of Llanfyllyn to the north-east and the village of Meifod to the south-east on a fine sunny day.

The summit of the hill is not on open access land so 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.

The name of the hill is Moel Llaethbwlch and the listing it is now a part of is named Y Trichant and these are the 300m height band of hills within the Twmpau (thirty welsh metre prominences and upward).  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 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 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 surveyed Trimble height, or a previous estimated summit height based on interpolation of contours.  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 for detailing these revisions.

The summit of this hill is easily distinguishable 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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