Thursday, 4 February 2016

Mapping Mountains – Hill Reclassifications – 200m Twmpau

Bwlch Clump (SJ 170 108) - 200m Twmpau reclassified to 200m Sub-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 twin map heighted summits and is situated to the south-east of Dyffryn Meifod and to the north-west of the Maesmawr valley and forms part of the Carnedd Wen range of hills.

These details are retrospective, as the Trimble GeoXH 6000 survey that resulted in this hill’s reclassification from a P30 Twmpau hill to a 200m Sub- Twmpau hill was conducted in the afternoon of the 20th January 2016 on a beautiful crisp winter day in good, dry and sunny conditions.

The lower section of the hill can be accessed from public footpaths to its west and east.  However, its summit does not appear on open access ground, therefore permission to visit the high point should be sought.

The hill was originally included in the main 200m P30 list that appeared on Geoff Crowder’s website as a single summit under the current 1:25,000 Explorer map height of 262m (SJ 173 109), and listed under the partly invented name of Pen y Bryn Wood (Bryn Wood being the name of the wood to the north-east of the originally listed hill’s summit).  The hill gained a twin summit when the Ordnance Survey enlarged map on the Geograph website included a 262m spot height for the adjacent hill at SJ 170 108, which was named as Bwlch Clump on this map.  According to map contours the drop between each was not sufficient for both to be included as P30s, with interpolation suggesting c 19m of drop.

Therefore the purpose of this survey was to ascertain which of the two summits is higher and separate their twin top status, and see if the drop between each was sufficient for the lower Trimbled summit to be included as a Sub-Twmpau and ascertain if the higher summit retained its P30 status, as the listed drop value for this hill was c 30m, which was based on bwlch contour interpolation.

The survey results for this once twin topped P30 are:

Pt . 262.8m (originally listed as Pen y Bryn Wood)

262.8m (converted to OSGM15) summit at SJ 17354 10914

243.5m (converted to OSGM15) bwlch at SJ 17190 10797

19.4m drop

Bwlch Clump

263.9m (converted to OSGM15) summit at SJ 17063 10813

234.9m (converted to OSGM15) bwlch at SJ 17089 10581

29.1m drop

Therefore the survey with the Trimble GeoXH 6000 confirms that Bwlch Clump is 1.1m higher than Pt. 262.8m, and that Pt. 262.8m has 19.4m of drop and is not listed as a Sub-Twmpau, and that Bwlch Clump has 29.1m of drop and is therefore reclassified to a 200m Sub-Twmpau.

The full details for the new status of this hill are:

Cardinal Hill:  Carnedd Wen

Summit Height:  263.9m (converted to OSGM15)

Name:  Bwlch Clump

OS 1:50,000 map:  125

Summit Grid Reference:  SJ 17063 10813

Drop:  29.1m (converted to OSGM15)

Pt. 262.8m - now reclassified from a twin topped P30 to a non Sub-Twmpau.  How the mighty fall!!!

Bwlch Clump - now reclassified from a twin topped P30 to a 200m Sub-Twmpau

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

Myrddyn Phillips (January 2016)

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