Thursday, 24 September 2015

Mapping Mountains – Significant Height Revisions – 100m Twmpau

Bryn Mawr (SJ 251 190)

This is the seventeenth 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 8th August 2015.

The seventeenth major height revision initiated from a survey with the Trimble GeoXH 6000 was conducted in the lower hills of the Carnedd Wen range, above the small community of Four Crosses which is situated beside the Afon Efyrnwy (River Vyrnwy) and part of the Montgomeryshire Canal.

The hill was surveyed in the company of Alex Cameron during a multi hill bagging day when the weather was set fine and we visited nine P30 Twmpau hills with seven of them being Trimbled.

The hill is listed as a 100m Twmpau (thirty welsh metre prominences and upward) and it has a 170m uppermost contour ring on current Ordnance Survey maps which have contour intervals at 5m.  The hill has been listed with an estimated height of c 174m based on the dimensions of the uppermost contour in relation to the steepness of the surrounding ground.

Access to the hill is good from west of its summit, as there is sufficient parking close to a gate that accesses a field to another gate which leads on to the hill.  However, the upper section is overgrown and the ancient earthen embankments of its hill fort are now immersed in long grass, nettles and brambles.  The summit is easily identified and the hill is recommended as there is a peaceful ambiance to it.

The name of the hill is Bryn Mawr and prior to the survey with the Trimble GeoXH 6000 the height of the hill was estimated as being c 174m based on 5m contour intervals on current Ordnance Survey maps, and to my knowledge no height has ever appeared on an Ordnance Survey map for this hill.

Therefore this hill’s new summit height is 178.1m (converted to OSGM15) which is 4.1m higher than its previously estimated height of c 174m and 8.1m higher than its uppermost ring contour on current Ordnance Survey maps.

The full details for the hill are:

Cardinal Hill:  Carnedd Wen

Summit Height (New Height):  178.1m (converted to OSGM15)

Name:  Bryn Mawr

OS 1:50,000 map:  126

Summit Grid Reference:  SJ 25117 19054
Drop:  90m

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

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