Pen y Gadair Fawr (SO
229 287) – 800m Twmpau reclassified to 700m Twmpau
There has been a reclassification to the listing of Twmpau (thirty welsh metre prominences
and upward) hills due to analysis of LIDAR data by Aled Williams. The hill was listed in the 800m height band
of P30 Twmpau hills and it has now
been reclassified to a 700m Twmpau.
The criteria for 700m
Twmpau status is all Welsh hills at or above 700m and below 800m in height
with 30m minimum drop, whilst the criteria for 800m Twmpau status is all Welsh hills at or above 800m and below
900m in height with 30m minimum drop.
Details to the 700m Twmpau
were published on Mapping Mountains on 15th April 2015, and details
to the 800m Twmpau were published on Mapping Mountains on
the 15th March 2015.
The name of the hill is Pen y Gadair Fawr and it had been
listed in the 800m height band of Twmpau
hills, based on the 800m summit spot height that appears on Ordnance Survey
1:50,000 Landranger and 1:25,000 Explorer maps.
With the 800m height on Ordnance Survey maps originating from the 2624ft
(799.8m) imperial bench mark height on the series of old Six-Inch maps.
The hill is situated on one of the central ridges
that forms the Mynyddoedd Duon (Black Mountains) group of hills with its
Cardinal Hill being Waun Fach (SO 215 299) and is placed in the Region of South
Wales (Region C, Sub-Region C3). It is
situated between the steam valleys of the Grwyne Fawr to its north-east and the
Grwyne Fechan to its south, with the town of Talgarth towards the north-west
and Y Gelli Gandryll (Hay-on-Wye) towards the north.
As the hill is a part of designated open access
land it can be accessed from most directions, however an extended circular walk
taking in the ridge upon which it is positioned in conjunction with the ridge
to its west is a good way to accustom oneself with this hill range.
The reclassification of Pen y Gadair Fawr to 700m Twmpau status is due to the
analysis of LIDAR data by Aled Williams.
LIDAR
(Light Detection & Ranging) is highly accurate height data that is now
freely available for much of England and Wales.
Aled’s analysis of LIDAR data gives the hill the
following details:
Pen y Gadair Fawr
Summit Height: 799.8m
Summit Grid Reference:
SO 22944 28758
Bwlch Height: 753.2m
Bwlch Grid Reference:
SO 22657 29359
Drop: 46.6m
Therefore, the 799.8m LIDAR data produced for the
summit position at SO 22944 28758 and
the 753.2m LIDAR data produced for the bwlch position at SO
22657 29359 gives this hill 46.6m of drop, and as the summit height is below
800m it is reclassified to a 700m Twmpau
with a 799.8m summit height.
This now revises the total in the 800m and 700m Twmpau
which will be updated accordingly.
The full details for the hill are:
Cardinal Hill: Waun
Fach
Summit Height: 799.8m
(LIDAR data)
Name: Pen y Gadair
Fawr
OS 1:50,000 map: 161
Summit Grid Reference:
SO 22944 28758
Drop: 46.6m (LIDAR data)
Pen y Gadair Fawr (SO 229 287) now reclassified from an 800m Twmpau to a 700m Twmpau |
My thanks to Aled Williams for sending the details of this
hill to me
Myrddyn Phillips (October 2017)
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