Craig y Merwydd (SH 644 134) –
200m Sub-Twmpau reclassified to 200m Twmpau
There has been confirmation of a reclassification to the 200m Twmpau list due to LIDAR analysis conducted by Myrddyn Phillips and subsequently confirmed via a survey with the Trimble GeoXH 6000, with the criteria for this list being:
200m Twmpau - Welsh hills at and above 200m and below 300m in height with 30m
minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau with the criteria for this sub category being all
Welsh hills at and above 200m and below 300m in height with 20m and more and
below 30m of drop, with the word Twmpau
being an acronym standing for thirty
welsh metre prominences and upward.
This hill was listed in the Hills to be surveyed sub list when the original Welsh P30 hills
were published on Geoff Crowder’s v-g.me website as it did not meet the
criteria then used for the main P30 list; however this list has now been
standardised and interpolated heights and drop values also included, resulting
in this hill being listed with an estimated c 32m of drop, based on the 296m summit
spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an
estimated bwlch height of c 264m based on bwlch contouring between 260m – 270m. This drop value was later amended to c 33m
based on the larger scaled contours on the Ordnance Survey Interactive Coverage
Map hosted on the Geograph website.
The name of the hill is Craig
y Merwydd (composition given as Craigymerwydd on contemporary maps) and it is
adjoined to the Cadair Idris group of hills, which are situated in the south-western part of North Wales
(Region A, Sub-Region A3), and the hill is positioned overlooking the A 493
road to its north-west and has the small community of Arthog to the north.
Craig y Merwydd (SH 644 134) |
Extract from the Ordnance Survey series of Six-Inch maps |
As the upper section of the hill is a part of designated open access land an ascent from most directions is feasible, with a minor road to its immediate south giving the easiest option.
The confirmation of the reclassification
of Craig y Merwydd to 200m Twmpau
status is due to LIDAR analysis conducted by Myrddyn Phillips. The LIDAR (Light Detection & Ranging)
technique produced highly accurate height data that is now freely available for
much of England and Wales.
The 1m DTM LIDAR analysis gives the hill the
following details:
Name: Craig y Merwydd
Summit Height: 295.5m
Summit Grid Reference:
SH 64413 13459
Bwlch Height: 261.0m
Bwlch Grid Reference:
SH 64606 13315
Drop: 34.5m
LIDAR image of Craig y Merwydd |
Therefore, the 295.5m LIDAR analysis for the
summit position at SH 64413 13459 and the 261.0m LIDAR analysis for
the bwlch position at SH 64606 13315 gives this hill 34.5m of drop, with the details from the Trimble GeoXH 6000 survey being 295.7m (converted to OSGM15) summit at SH 64413 13459 and 261.2m (converted to OSGM15) bwlch at SH 64605 13317, giving this hill 34.6m of drop, which
confirms its reclassification to 200m Twmpau status.
The full details for the hill are:
Group: Cadair Idris
Name: Craig y Merwydd
OS 1:50,000 map: 124
Summit Height: 295.7m
(converted to OSGM15)
Summit Grid
Reference: SH 64413 13459
Bwlch
Height: 261.2m (converted to OSGM15)
Bwlch Grid
Reference: SH 64605 13317
Drop: 34.6m (converted to OSGM15)
For details on the survey of Craig y Merwydd
The Trimble GeoXH 6000 gathering data at the summit of Craig y Merwydd |
For details on the survey of Craig y Merwydd
Myrddyn Phillips (May 2018)
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