Pen y Bwlch Coch (SH 751 159) – 390m Double Sub-Pedwar
reclassified to 390m Sub-Pedwar
There has been a reclassification to the listing
of the Y Pedwarau – The 400m Hills of
Wales, with the summit height, bwlch height and their locations, the drop
and status of the hill derived from detail produced by Joe Nuttall in his surface
analysis progamme, with subsequent LIDAR analysis conducted by the DoBIH team
and independently by Myrddyn Phillips.
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LIDAR image of Pen y Bwlch Coch (SH 751 159) |
The criteria for the list that this
reclassification applies to are:
Y Pedwarau – The 400m Hills of Wales.
Welsh hills at or above 400m and below 500m in height that have 30m
minimum drop, accompanying the main Y Pedwarau list are five categories of sub
hills, with this hill being reclassified from the 390m Double Sub-Pedwar
category to the 390m Sub-Pedwar category.
The criteria for the former being all Welsh hills at or above 390m and
below 400m in height that have 20m or more and below 30m of drop, with the
criteria for the latter being all Welsh hills at or above 390m and below 400m
in height that have 30m minimum drop.
The list is co-authored by Myrddyn Phillips and Aled Williams and is published on Mapping Mountains in Google Doc format.
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Y Pedwarau - The 400m Hills of Wales by Myrddyn Phillips and Aled Williams |
The name the hill is listed by is Pen y Bwlch
Coch, 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
it is positioned with the A470 road to its north and the A487 road to its east,
and has the town of Dolgellau towards the north-west.
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Extract from the Ordnance Survey 1:25,000 Explorer map |
After the sub list was standardised, and
interpolated heights and drop values also included the details for this hill
were re-evaluated and it was listed with 26m of drop, based on the 395m summit
spot height that appears on the Ordnance Survey 1:50,000 Landranger map and the
369m bwlch spot height that appeared on the Ordnance Survey Vector Map Local
hosted on the Geograph website which was entitled the Interactive Coverage Map,
however it was noted that the latter spot height was not centralised where
interpolation would place the critical point of the bwlch, and these were the
values this hill was listed by when the 1st edition of the Y Pedwarau was published by Europeaklist
in May 2013.
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Extract from the Ordnance Survey 1:50,000 Landranger map |
One of the resources recently available online is
the mapping on the OS Maps website and the details for this hill were
subsequently re-assessed against this mapping.
This is the replacement for OS Get-a-map and until recent times had
contours at 5m intervals which were proving consistently more accurate compared
to the 5m contours that sometimes appear on the Ordnance Survey 1:25,000
Explorer map and used to appear on the online Vector Map Local. This mapping had bwlch contouring between
365m – 370m, with interpolation placing the height of the bwlch as an estimated
c 366m, and when coupled with the 395m summit spot height these values gave
this hill an estimated c 29m of drop.
However, it was not until LIDAR became available
that the details for this hill could be accurately re-assessed. The LIDAR (Light Detection & Ranging)
technique produced highly accurate height data that is now freely available for
much of England and Wales.
Therefore, the reclassification of this hill from 390m
Double Sub-Pedwar status is due to LIDAR analysis, resulting in a 395.1m summit
height and a 364.9m bwlch height, with these values giving this hill 30.2m of
drop, which is sufficient for it to be classified as a 390m Sub-Pedwar.
The full details for the hill are:
Group: Cadair Idris
Name: Pen y Bwlch Coch
OS 1:50,000 map: 124
Summit Height: 395.1m (LIDAR)
Summit Grid
Reference: SH 75190 15937 (LIDAR)
Bwlch Height: 364.9m (LIDAR)
Bwlch Grid
Reference: SH 75107 15780 (LIDAR)
Drop: 30.2m (LIDAR)
For the additions, reclassifications and deletions to Y Pedwarau – The 400m Hills of Wales reported
on Mapping Mountains since the May 2013 publication of the list by Europeaklist
please consult the following Change Registers:
Y Pedwarau
Y Pedwarau – 400m Sub-Pedwarau
Y Pedwarau – 390m Sub-Pedwarau
Y Pedwarau – 390m Double Sub-Pedwarau
Myrddyn Phillips and Aled Williams (September 2023)
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