Pt. 408.0m, Hirfynydd (SN 822 051) - 400m Sub-Pedwar deletion
There has been a deletion of a 400m Sub-Pedwar by analysis of
LIDAR data by Aled Williams. The 400m Sub-Pedwarau are the Welsh hills at or above 400m and below 500m in height with
a drop between 20m and below 30m.
The hill is connected to the Fforest Fawr group of
hills with its Cardinal Hill being Hirfynydd (SN 839 076) and is placed in the
Region of South Wales (C-2). The hill is
positioned above the villages of Y Creunant (Crynant) in Cwm Dulais (Dulais
Valley) to its west and Resolfen (Resolven) in Cwm Nedd (Vale of Neath) to its
south, and is best ascended via Sarn Helen; the ancient Roman Road that follows
the ridge crest toward the higher connecting hill of Hirfynydd.
As the authors do not know an individual name for
the hill we are following the extended point (Pt. 408.0m) notation principal
and listing it as Pt. 408.0m, Hirfynydd, and prior to the analysis of LIDAR
data the hill was listed with c 20m of drop based on a 408m summit spot height on
the Ordnance Survey 1:25,000 Explorer map and an estimated bwlch height from
contour interpolation of c 388m.
As Aled was analysing other hills in the vicinity
against LIDAR data, he did likewise with Pt. 408.0m, Hirfynydd. 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:
Pt.
408.0m, Hirfynydd
Summit
Height: 408.0m
Summit
Grid Reference: SN 82213 05117
Bwlch
Height: 389.5m
Bwlch
Grid Reference: SN 82356 05671
Drop: 18.5m
Therefore, the 408.0m LIDAR data produced for the
summit position at SN 82213 05117 and
the 389.5m LIDAR data produced for the bwlch position at SN
82356 05671 is insufficient for this hill
to retain its 400m Sub-Pedwar status with only 18.5m of drop, and therefore Pt.
408m, Hirfynydd is deleted from the listing of 400m Sub-Pedwar hills and the list of the Y Pedwarau will be updated accordingly.
The list of Pedwar hills is available from the Haroldstreet website
(January 2014) with all subsequent changes available via the Mapping Mountains
site.
The full details for the hill are:
Cardinal Hill: Hirfynydd
Summit Height: 408.0m
(LIDAR data)
Name: Pt. 408m,
Hirfynydd
OS 1:50,000 map: 160
Summit Grid Reference: SN 82213 05117
Drop: 18.5m (LIDAR
data)
The list of additions, reclassifications and deletions from
the 400m Sub-Pedwar list since the 1st edition of the Y Pedwarau was
published by Europeaklist are as follows:
400m SUB-PEDWAR ADDITIONS
Pt. 422.3m (converted to OSGM15) (SO 073 822) Pedwar reclassified to 400m Sub-Pedwar with 29.0m drop
Pt. 407.7m (converted to OSGM15) (SO 180 692) Pedwar reclassified to 400m Sub-Pedwar with 28.3m drop
400m SUB-PEDWAR RECLASSIFICATIONS
Pt. 499.5m (converted to OSGM15) (SH 665 310) 400m Sub-Pedwar reclassified to Pedwar with 30.3m drop
400m SUB-PEDWAR DELETIONS
Pt. 408.0m, Hirfynydd (LIDAR data) (SN 822 051) 18.5m drop
Myrddyn Phillips and Aled Williams (December 2016)
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