Clogwyn Drain (SH 652 493) – Uchaf
addition
There has been an addition to the listing of The Welsh Highlands – Uchafion Cymru due
to analysis of 5m contouring on the OS Maps website coupled with spot height
data on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000
Explorer map.
The criteria for the list that this addition applies to are:
The Welsh Highlands –
Uchafion Cymru
– This is the revised draft title for the Welsh 500m P15s list that takes
in all hills in Wales at or above 500m in height with 15m minimum drop. The list is co-authored by Myrddyn Phillips
and Aled Williams with the introduction to the list being published on Mapping Mountains in November 2015 and an update relating to the list appearing on Mapping Mountains on the 19th June 2019.
The name of the hill is Clogwyn
Drain and it is adjoined to the Moelwynion group of hills, which are situated in the north-western part of
North Wales (Region A, Sub-Region A1), and is positioned with the A498 road to its north-west and the A470
road to its east, and has the village of Beddgelert towards the west south-west
and the town of Blaenau Ffestiniog towards the south-east.
During the initial compilation of the original
list of Welsh 500m P15s that later became known as Yr Uchafion and latterly as The
Welsh Highlands – Uchafion Cymru, this hill was included as an Uchaf with
19m of drop based on a basic levelling survey conducted by Myrddyn Phillips on
the 25th May 2004.
However, this survey was conducted at the end of a
long day on the hill which involved many such surveys and as contemporary
Ordnance Survey maps of the day gave a 508m summit spot height and bwlch
contouring between 490m – 500m, it meant that if this survey and the summit
spot height were accurate the height of the bwlch would be below that of its
lower 490m contour. Because of this the
survey result was questioned and the hill taken out of the list.
 |
| Extract from the Ordnance Survey 1:25,000 Explorer map |
The details for this hill were re-examined when
the Ordnance Survey Vector Map Local hosted on the Geograph website and which
is entitled the Interactive Coverage Map became available online. This mapping has many spot heights not on any
other publicly available Ordnance Survey map and gives a 498m spot height positioned
at SH 65212 49275 on the bwlch area of this hill. This spot height is also shown on Ordnance
Survey data that appears on the Magic Maps website. When coupled with the 508m summit spot height
these values gave this hill 10m of drop and the questionable accuracy of the
basic levelling survey seemed to be substantiated.
 |
| Extract from the Magic Maps website |
The details for this hill were re-assessed when
the OS Maps website became available online.
This is the replacement for OS Get-a-map and has contours at 5m
intervals which are proving consistently more accurate compared to the 5m
contours that sometimes appear on Ordnance Survey 1:25,000 Explorer maps and
the online Vector Map Local. This
mapping has an uppermost 505m contour and bwlch contouring between 490m – 495m
and places the position of the 498m spot height above the 495m contour line,
indicating that the spot height is not placed at the critical point of the
bwlch. This re-assessment resulted in
the hill being listed with an estimated c 15m of drop.
 |
| Extract from OS Maps |
Therefore, the addition of this hill to Uchaf
status is due to the 508m summit spot height that appears on contemporary
1:50,000 Landranger and 1:25,000 Explorer maps and an estimated bwlch height of
c 493m based on 5m contouring on the OS Maps website between 490m – 495m, with
these values giving this hill c 15m of drop which is sufficient for Uchaf
status.
The full details for the hill are:
Group: Moelwynion
Name: Clogwyn Drain
OS 1:50,000 map: 115
Summit Height: 508m (spot
height)
Summit Grid Reference:
SH 65200 49356 (spot height)
Bwlch Height: c 493m (interpolation)
Bwlch Grid Reference:
SH 65239 49257 (interpolation)
Drop: c 15m (spot
height summit and interpolated bwlch)
For the additions, deletions and reclassifications to The Welsh Highlands – Uchafion Cymru
reported on Mapping Mountains please consult the following Change Registers:
Aled Williams and Myrddyn Phillips (January 2020)
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