Mapping Mountains – Summit Relocations – Y Pedwarau

Llethr Melyn (SN 959 579)

There is a Summit Relocation to the Y Pedwarau list initiated by a survey with the Trimble GeoXH 6000.  The Y Pedwarau are the 400m hills of Wales that have 30m minimum drop, with the following details being retrospective as the survey that resulted in this summit relocation was conducted on 23^th May 2015.

The survey was conducted in the eastern Elenydd on a fine day during a circuit of seven hills, and the hill is situated to the north north-west of the small community of Llanafan-fawr.

The name of the hill is Llethr Melyn, and its summit area has three separate ring contours that have a 433m spot height on current Ordnance Survey maps, with a fourth point to the south having a 430m triangulation pillar on it.

The position of each of these 433m spot heights was surveyed, as was the highest ground beside the trig pillar as well as a fifth point that visually looked as high as any other.

The survey results appear below:

Summit 1:  430.9m (converted to OSGM15)  at SN 96347 57664

Summit 2:  432.4m (converted to OSGM15) at SN 95948 57974

Summit 3:  433.0m (converted to OSGM15) at SN 95967 57997

Summit 4:  432.6m (converted to OSGM15) at SN 96031 58035

Summit 5:  431.5m (converted to OSGM15)  at SN 96301 58100

Summit 1 is where the 43om triangulation pillar is situated and Summits 2, 4 and 5 are where the three 433m map spot heights appear on the ground.  However, the highest point surveyed with the Trimble GeoXH 6000 was Summit 3 which has no spot height adjoined to it on current Ordnance Survey maps.

The summit that was prioritised in the listing of the Y Pedwarau was at SN 960 580 with the other two summits of equal map height being mentioned in the Notes section that accompanied the Europeaklist publication.

The position of the relocated summit is at SN 95967 57997 and is the top of a small outcrop of rock, this is not given a spot height on current Ordnance Survey maps but the survey result produced by the Trimble  GeoXH 6000 gave it as 0.4m higher when compared to the next highest point surveyed.

The full details for the hill are:

Cardinal Hill:  Gorllwyn

Summit Height:  433.0m (converted to OSGM15)

Name:  Llethr Melyn

OS 1:50,000 map:  147

Summit Grid Reference (New Position):  SN 95967 57997 

 

Drop:  38.9m (Trimble summit and LIDAR bwlch)

The Trimble GeoXH 6000 gathering data at the new summit position of Llethr Melyn, with the old position of the prioritised summit in the background of this photograph

For details on the survey that relocated the summit of this hill please click {here}

Myrddyn Phillips and Aled Willams (May 2015)