Dinas Dinorwig (SH 549
652)
There has been a Summit Relocation to a hill that
is listed in the 100m Twmpau, with
the summit height and its location, and the drop of the hill being confirmed by
LIDAR analysis conducted by Myrddyn Phillips.
 |
| Dinas Dinorwig (SH 549 652) |
The criteria for the list that this summit relocation applies
to are:
100m Twmpau - Welsh hills at or above 100m and below 200m in height with 30m minimum
drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all
Welsh hills at or above 100m and below 200m in height with 20m or more and
below 30m of drop, with the word Twmpau
being an acronym standing for thirty
welsh metre prominences and upward.
The name of the hill is Dinas
Dinorwig and it is adjoined to the Glyderau group of hills, which are situated in the north-western part of
North Wales (Region A, Sub-Region A1), and
it is encircled by an old track to its north and minor roads to its west, south
and east, with the B4366 to its north-west and the A4244 to its north-east, and
has the small communities of Bethel towards the west, Rhiwlas towards the east
and Llanrug towards the south-west.
Prior to LIDAR analysis this hill was listed with 38m
of drop based on its 170m summit spot height positioned at SH 54966 65306 that
appears on the Ordnance Survey 1:25,000 Explorer map (with the 1:50,000
Landranger map giving a 169m summit spot height) and a bwlch height of 132m based
on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map.
 |
| Extract from the Ordnance Survey 1:25,000 Explorer map |
The upper part of this hill comprises an ancient
Iron Age Hillfort that has a series of steep embankments and ditches which are in
the main overgrown with brambles, bracken and small trees, whilst the inner
central part used to be grazed and is now a paddock with an extremely friendly
horse when I last visited. It is this
inner central part of the summit area where the 170m spot height is positioned.
 |
| LIDAR image of Dinas Dinorwig |
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 Dinas Dinorwig |
The summit height produced by LIDAR analysis is 169.6m
and is positioned at SH 54955 65254, this position is to the highest part of
the ancient embankments, whereas the height produced by LIDAR analysis to the
high point of the inner central part of the hill is 169.0m and is positioned at
SH 54964 65302, this latter point was surveyed with the Trimble GeoXH 6000 as
being 169.2m in height. As the location
of this hill’s listed summit is to a different feature compared to its
previously listed summit this
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 listed summit is
relocated to a different feature compared to its previous listed position, or
when the summit of the hill is in a different field compared to where
previously given, 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.
As heights on different scaled Ordnance Survey maps are not consistent
the height given on the 1:25,000 Explorer map is being prioritised in favour of
the 1:50,000 Landranger map for detailing these relocations.
 |
| The Trimble set-up position with the very friendly horse at the old listed summit position of Dinas Dinorwig |
Therefore the height produced by LIDAR analysis is
169.6m and this is positioned at SH 54955 65254, this position is approximately
50 metres south from where the 170m spot height appears on Ordnance Survey 1:25,000
Explorer maps and which was surveyed as being 169.2m in height, and importantly
the new summit position is to a different feature.
 |
| The summit of Dinas Dinorwig |
The full details for the hill are:
Group: Glyderau
Name: Dinas Dinorwig
OS 1:50,000 map: 114,
115
Summit Height: 169.6m
(LIDAR)
Summit Grid Reference (new position): SH 54955 65254 (LIDAR)
Bwlch Height: 131.8m (LIDAR)
Bwlch Grid Reference: SH 54648 64645 (LIDAR)
Drop: 37.8m (LIDAR)
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