Friday, 11 March 2016

Mapping Mountains – Hill Reclassifications – 200m Twmpau

Gallt y Celyn (SH 811 542) - 200m Sub-Twmpau reclassified to 200m Twmpau

There has been a reclassification within the 200m Twmpau (thirty welsh metre prominences and upward) hill list instigated by a survey with the Trimble GeoXH 6000.   The hill has a convoluted history of reclassification and is situated just to the north of the A 5 and southward of the small community of Capel Garmon and south-eastward of the town of Betws-y-coed, and is positioned in the Mynydd Hiraethog range of hills.

The Trimble GeoXH 6000 survey that resulted in this hill’s reclassification from a 200m Sub-Twmpau to a 200m Twmpau was conducted in the afternoon of the 23th February 2016 on a beautiful winter’s day in good, dry and sunny conditions.

The hill is unnamed on current Ordnance Survey maps but is given as a part of Gallt y Celyn on the Tithe map and therefore this name is deemed appropriate to use.
Access to the hill is relatively easy as there is a public footpath approaching from the north which can be accessed from Capel Garmon, and also one from the south-east which can be accessed from a steep minor lane that heads north from the A 5.  The summit of the hill is only a short distance from where these footpaths meet and is on open access land.

The hill has a convoluted history of inclusion and exclusion from the 200m P30 Welsh list as it was originally included in the ‘Hills to Survey’ Sub-List that accompanied the main P30 lists on Geoff Crowder’s website.  This Sub-List was reliant upon the details on Ordnance Survey maps being correct and did not take in contour interpolation for inclusion within the main P30 list.  After the Sub-List was standardised and contour interpolation used, the hill was reclassified to a P30 with c 30m of drop, based on a 258m summit spot height and an estimated bwlch height of c 238m.  To complicate matters this hill had twin tops, both given a 258m spot height on Ordnance Survey maps, these tops were surveyed with the Trimble on the 24th December 2013 with the following results:

257.610m (converted to OSGM15) at SH 81121 54259.

257.093m (converted to OSGM15) at SH 81007 54476.

Although the twin tops had been separated the bwlch was not surveyed and as it was estimated to be c 238m high, the drop for this hill was accepted as being just under the qualifying minimum drop of 30m and therefore the hill re-joined the ranks of Subs.

It was always my intention to survey the bwlch and determine once and for all the classification of the hill, and on the 23rd February I found myself immersed in a water laden bog gathering the allotted five minutes of data.  This survey resulted in a bwlch height of 227.5m (227.529m, converted to OSGM15), which gave this hill 30.1m (30.081m) of drop, and therefore it re-joins the ranks of P30 Twmpau hills.

The full details for the hill are:

Cardinal Hill:  Mwdwl Eithin

Summit Height:  257.6m (converted to OSGM15)

Name:  Gallt y Celyn

OS 1:50,000 map:  116

Summit Grid Reference:  SH 811 542

Drop:  30.1m (converted to OSGM15)

Gallt y Celyn (SH 811 542) in the centre foreground of this photograph and which has now been re-instated as a 200m P30 Twmpau.  Photograph taken from the summit of Dinas Mawr (SH 808 539)

For details on the survey that resulted in this hill being reclassified from a 200m Sub-Twmpau to a 200m Twmpau please click {here} for summit and {here} for the bwlch survey.

Myrddyn Phillips (February 2016)

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