Grugfryn (SJ 248 356)
There has been a Summit Relocation to a hill that
is listed in the
Y Pedwarau – The 400m Hills of Wales,
with the summit height and its position confirmed
from LIDAR analysis conducted by Aled Williams.
 |
| Grugfryn (SJ 248 356) |
The criteria for the list this
summit relocation affects are:
Y Pedwarau – The 400m Hills of Wales. Welsh hills at or above 400m and below 500m in height with 30m minimum drop, the list is co-authored by Myrddyn Phillips and Aled Williams and is published on Mapping Mountains in Google Doc format.
The name of the hill is Grugfryn and it is adjoined to the Y
Berwyn group of hills, which are situated in the south-eastern part of North Wales (Region A,
Sub-Region A4), and
it is encircled by minor roads with the B4579 road to its south-west, and has
the village of Glyn Ceiriog towards the west north-west.
When the original 400m height band of Welsh P30
hills were published on Geoff Crowder’s v-g.me website the summit height of
this hill was listed as 403m which was based on the spot height positioned at
SJ 24849 35660 that appears on the Ordnance Survey 1:25,000 Explorer map.
 |
| Extract from the Ordnance Survey 1:25,000 Explorer map |
The upper section of this hill is immersed in a
conifer plantation and the 403m spot height appears adjacent to a forest track. This area was visited and a mound on the
western side of the track was surveyed with the Trimble GeoXH 6000, resulting
in a 404.05m height positioned at SJ 24842 35652.
 |
| The Trimble GeoXH 6000 gathering data from the mound beside the indistinct forest track |
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.
 |
| LIDAR summit image of Grugfryn |
The summit height produced by LIDAR analysis is 405.1m
at SJ 24835 35615 and its position in relation to that previously given comes within the
parameters of the Summit Relocations used within this page heading, these
parameters are:
The term Summit Relocations applies to any listed
hill whose summit meets the following criteria; where there are a number of
potential summit positions within close proximity and the highest point is not
where previously given, or a relocation of approximately 100 metres or more in
distance from either the position of a map spot height or from where the summit
of the hill was previously thought to exist, or when the summit of the hill is
in a different field compared to where previously given, or when it is
positioned to a different feature such as in a conifer plantation, or when the
natural and intact summit of a hill is confirmed compared to a higher point
such as a raised field boundary that is judged to be a relatively recent
man-made construct.
Therefore, the summit
height produced by LIDAR analysis is 405.1m and is positioned at SJ 24835 35615,
this position is not given a spot height on contemporary Ordnance Survey maps
and is approximately 38 metres southward from where the Trimble GeoXH 6000 survey
took place and approximately 50 metres southward from where the 403m spot
height appears on the Ordnance Survey 1:25,000 Explorer map.
The full details for the hill are:
Group: Y Berwyn
Name: Grugfryn
OS 1:50,000 map: 126
Summit Height: 405.1m (LIDAR)
Summit Grid Reference (New Position): SJ 24835 35615 (LIDAR)
Bwlch Height: 361.9m (LIDAR)
Bwlch Grid Reference:
SJ 24456 36336 (LIDAR)
Drop: 43.2m (LIDAR)
Myrddyn Phillips and Aled Williams (November 2019)
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