Parc Llwyn Du (SN 428 188)
There has been a Summit Relocation to a hill that
is listed in the 100m Twmpau, with
the summit height and its location, drop and status of the hill initially
confirmed by LIDAR analysis and subsequently by a summit survey with the
Trimble GeoXH 6000 which were conducted by Myrddyn Phillips, with latter taking
place on the 31st July 2018.
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| Parc Llwyn Du (SN 428 188) |
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 bounded land
where the summit of this hill is situated is Parc Llwyn Du and this was derived
from the Tithe map, and it is the name that this hill is now listed by. The hill is adjoined to the Mynydd Sylen
group of hills, which are situated in
the western part of South Wales (Region C, Sub-Region C1), and is positioned
with the A 48 road to its south and the B 4300 road to its north, and has the
town of Caerfyrddin (Carmarthen) to the north-west.
If wanting to visit the hill
permission to do so should be sought as the summit area is not a part of
designated open access land, for those wishing to do so the nearest public
footpath is to the south of the summit.
When the original Welsh 100m P30 list was published
on Geoff Crowder’s v-g.me website the summit location of this hill was given to
the 104m spot height adjoined to a triangulation pillar that appeared on
contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps and
positioned at SN 423 186. However, this trig
pillar is placed on a covered reservoir that is considered a recent man-made
construct and therefore not a part of the natural summit of the hill.
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| Extract from the Ordnance Survey 1:25,000 Explorer map |
The details for this hill were re-examined when
the Ordnance Survey Interactive Coverage Map hosted on the Geograph website became
available online and this map also gave a 104m spot height positioned at SN 428
188, and which is placed on natural ground.
However, it was not until LIDAR became available that an accurate height
comparison could be made between these two positions.
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| Extract from the Ordnance Survey Interactive Coverage Map hosted on the Geograph website |
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| LIDAR image of Parc Llwyn Du |
The summit height produced by DTM LIDAR analysis
is 104.1m at SN 42895 18829, with the summit subsequently surveyed using the Trimble
GeoXH 6000 resulting in a 104.3m summit height positioned at SN 42895 18827, and
its position in relation to that originally 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 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 summit height produced by the Trimble GeoXH 6000 is 104.3m and is positioned at SN
42895 18827, this position is approximately 30 metres east from where the 104m
spot height appears on the Ordnance Survey Interactive Coverage Map hosted on
the Geograph website, and over 560 metres east north-eastward from where the
summit was originally listed at this hill’s triangulation pillar.
The full details for the hill are:
Group: Mynydd Sylen
Name: Parc Llwyn Du
OS 1:50,000 map: 159
Summit Height: 104.3m (converted
to OSGM15, natural summit)
Summit Grid Reference (new position): SN 42895 18827
Bwlch Height: 73.4m (LIDAR)
Bwlch Grid Reference: SN 43247 18917 (LIDAR)
Drop: 30.8m (Trimble
summit and LIDAR bwlch)
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| The Trimble set-up position at the summit of Parc Llwyn Du |
Myrddyn Phillips (January 2019)
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