Bryn Bach (SS 903 875)
There has been confirmation of a Summit Relocation
to a hill that is listed in the 100m
Twmpau, with the summit height, bwlch height and their locations, the drop
and status of the hill being confirmed by LIDAR analysis conducted by Myrddyn
Phillips.
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| LIDAR image of Bryn Bach |
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 Bryn Bach, and this was
derived from the Ordnance Survey One-Inch ‘Old Series’ map and it is this name
that the hill is now listed by, and it is adjoined to the Cymoedd Morgannwg
group of hills, which are situated in the central
part of South Wales (Region C, Sub-Region C2), and is positioned with the A4063 road and the Afon
Llynfi to its south-west and the A4064 road and the Afon Garw to its
south-east, and has the small community of Betws towards the south.
When this hill was originally listed in the 100m
height band of Welsh P30 hills on Geoff Crowder’s v-g.me website, its summit
was listed at SS900871 and it appeared with an accompanying note stating; Two points of same height – other at SS903875,
with these details being taken from the Ordnance Survey 1:25,000 Explorer
map.
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| Extract from the Ordnance Survey 1:25,000 Explorer map |
Prior to LIDAR analysis this hill was listed with an
estimated c 31m of drop, based on the 164m summit spot height that appears on
the Ordnance Survey Vector Map Local hosted on the Geograph website and which
is entitled the Interactive Coverage Map.
This spot height appears beside a field boundary at SS 90354 87551.
 |
| Extract from the Ordnance Survey Vector Map Local hosted on the Geograph website |
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.
The height produced by LIDAR analysis is 167.0m positioned
at SS 90364 87531, and is in a different field and not beside the field
boundary compared to the position of the 164m spot height, and confirms this
land is higher than the prioritised position originally given in the 100m P30
list of Geoff Crowder’s v-g.me website, and as such 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.
 |
| LIDAR summit image of Bryn Bach |
Therefore, the height produced by LIDAR analysis
is 167.0m to what is constituted natural ground and this is positioned at SS 90364
87531, this position is not given a spot height on Ordnance Survey maps and is
approximately 600 metres north-eastward from where the prioritised listed
summit was originally given and is positioned in a different field to where the
164m spot height appears on the Ordnance Survey Vector Map Local hosted on the
Geograph website.
The full details for the hill are:
Group: Cymoedd
Morgannwg
Name: Bryn Bach
OS 1:50,000 map: 170
Summit Height: 167.0m (LIDAR)
Summit Grid Reference (New Position): SS 90364 87531 (LIDAR)
Bwlch Height: 135.2m (LIDAR)
Bwlch Grid Reference:
SS 90511 87849 (LIDAR)
Drop: 31.9m (LIDAR)
Myrddyn Phillips (June 2019)
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