Bryniau (SH 579 711)
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 the latter taking
place on the 1st October 2018.
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| Bryniau (SH 579 711) |
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 land where the summit of
this hill is situated is a part of Bryniau and this was derived from local
enquiry and substantiated from the Tithe map, and it is the name that this hill
is now listed by. The hill 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 is positioned with the A4087
road to its west and minor roads to its south and east, and has the small city of Bangor towards its north.
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 easiest approach is
via a track leading to the old farmhouse of Bryniau.
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 117m spot height adjoined to a triangulation pillar that
appeared on contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000
Explorer maps and which is positioned at SH 578 711.
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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 gives a 118m spot height positioned to the
north-east of the trig pillar at SH 579 711.
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| Extract from the Ordnance Survey Interactive Coverage Map hosted on the Geograph website |
However, it was not until LIDAR became available
that these two positions could be compared and confirmation that the land where
the 118m spot height appears is higher than the land beside the 117 map
heighted trig pillar.
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| LIDAR image of Bryniau |
The summit height produced by the Trimble GeoXH
6000 survey is 117.6m, 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.
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| The Trimble GeoXH 6000 gathering data at the summit of Bryniau |
The summit height produced by the Trimble GeoXH
6000 is 117.6m and is positioned at SH 57971 71196, this position is
approximately 80 metres north-east from where the summit was originally listed
at this hill’s triangulation pillar.
The full details for the hill are:
Group: Glyderau
Name: Bryniau
OS 1:50,000 map: 114,
115
Summit Height: 117.6m (converted
to OSGM15)
Summit Grid Reference (new position): SH 57971 71196
Bwlch Height: 87.4m (LIDAR)
Bwlch Grid Reference: SH 57748 70845 (LIDAR)
Drop: 30.1m (Trimble
summit and LIDAR bwlch)
Myrddyn Phillips (February 2019)
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