Bryn Mawr (SH 765 766) – 100m
Sub-Twmpau reclassified to 100m Twmpau
There has been confirmation of a reclassification to a hill that is listed in the 100m Twmpau, with the summit height and its location, the drop and status of the hill confirmed by LIDAR analysis, and a subsequent summit survey with the Trimble GeoXH 6000, both conducted by Myrddyn Phillips with the latter taking place on the 15th October 2018.
Bryn Mawr (SH 765 766) |
The criteria for the list that this
reclassification 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
Mawr, and it is adjoined to the Carneddau group of hills, which are situated in the north-western part of
North Wales (Region A, Sub-Region A1), and
it is encircled by minor roads with the B5106 and the Afon Conwy (River Conwy)
to its east, and has the town of Conwy towards
its north-east.
When the original Welsh P30 hills were published
on Geoff Crowder’s v-g.me website this hill was included in the Hills to be surveyed sub list that
accompanied the 100m height band of P30 hills, as it did not at that stage meet
the criteria used in this list.
When the sub list was standardised, and
interpolated heights and drop values also included this hill was listed with an
estimated c 28m of drop, based on an estimated summit height of c 143m and an
estimated bwlch height of c 115m, with both based on interpolation of 10m contouring
on the Ordnance Survey 1:25,000 Explorer map.
Extract from the Ordnance Survey 1:25,000 Explorer map |
The drop value for this hill was re-assessed when
the Ordnance Survey Vector Map Local hosted on the Geograph website became available
online; this mapping is entitled the Interactive Coverage Map. Although this mapping still has no spot
heights for either summit or bwlch it does have 5m contouring which enabled a
better interpolation of height, and with an estimated c 143m summit and c 113m
bwlch it gave this hill an estimated c 30m of drop.
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.
LIDAR image of Bryn Mawr (SH 765 766) |
The confirmation of the reclassification of Bryn
Mawr to 100m Twmpau status is due to
LIDAR analysis and a subsequent summit survey with the Trimble GeoXH 6000
conducted by Myrddyn Phillips, resulting in a 114.0m summit height and a 110.7m
bwlch height, with these values giving this hill 33.3m of drop which is
sufficient for it to be classified as a 100m
Twmpau.
The full details for the hill are:
Group: Carneddau
Name: Bryn Mawr
OS 1:50,000 map: 115
Summit Height: 144.0m (converted
to OSGM15)
Summit Grid Reference:
SH
76562 76669
Bwlch Height:
110.7m (LIDAR)
Bwlch Grid Reference:
SH 76263 76359 (LIDAR)
Drop: 33.3m (Trimble
summit and LIDAR bwlch)
Myrddyn Phillips (April 2019)
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