Bryn y Bont (SH 596 459)
– Double Sub-Twmpau addition
There has been an addition to the listing of the Double Sub-Twmpau due to analysis conducted
by Aled Williams of data produced via LIDAR.
With the title of Twmpau being
an acronym for thirty welsh metre
prominences and upward.
Accompanying each 100m height band within the main Twmpau list is a sub list entitled the Sub-Twmpau, with the Double Sub-Twmpau attached to the lower
tier height band of Welsh hills.
The criteria for the lower tier of Twmpau hills are:
30-99m Twmpau – All Welsh hills at and
above 30m and below 100m in height with 30m minimum drop.
30-99m Sub-Twmpau – All Welsh hills at and
above 30m and below 100m in height with 20m or more and below 30m of drop.
Double Sub-Twmpau – All Welsh hills at and
above 20m and below 30m in height with 20m or more and below 30m of drop.
Prior to analysis of data produced via LIDAR this
hill was not listed in the Hills to be
surveyed sub list that accompanied the Welsh P30 lists published on Geoff
Crowder’s v-g.me website. When these lists
were re-evaluated after they were standardised and also drop values added, this
hill was listed with c 16m of drop based on an estimated c 20m summit height
which was based on this hill’s small uppermost 20m ring contour on Ordnance
Survey 1:50,000 Landranger and 1:25,000 Explorer maps, and an estimated bwlch
height of c 4m based on bwlch contouring at 10m intervals and between 0 – 10m,
with the caveat that the 4m spot height positioned at SH 59756 45814 and shown
on the Ordnance Survey 1:25,000 Explorer map is probably not at the position of
the critical bwlch.
The name of the hill is Bryn y Bont and it is
situated in the Moelwynion range of hills and is placed in the Region of North
Wales (Region A, Sub-Region A1). The
hill is positioned with the A 4085 road to its north and its east and the A 498
road to its west, and has the Afon Glaslyn also to its immediate west, with the
hamlet of Nantmor positioned to the east of the hill and the village of
Beddgelert towards its north.
As the hill is not a part of designated open
access land permission to visit should be sought, for those wishing to do so an
ascent from the convenience of the road to its north or east is likely to be
the easiest.
The addition of Bryn y Bont to Double Sub-Twmpau status is due to
analysis conducted by Aled Williams of data produced via LIDAR. The LIDAR (Light Detection & Ranging)
technique produced highly accurate height data that is now freely available for
much of England and Wales.
Aled’s analysis of the data produced via LIDAR
gives the hill the following details:
Bryn y Bont
Summit Height: 25.2m
Summit Grid Reference:
SH 59641 45973
Bwlch Height: 4.3m
Bwlch Grid Reference:
SH 59572 46137
Drop: 20.9m
Therefore, the 25.2m data produced via LIDAR for
the summit position at SH 59641 45973 and
the 4.3m data produced via LIDAR for the bwlch position at SH 59572
46137 gives this hill 20.9m of drop, which is sufficient for it to be
classified as a Double Sub-Twmpau.
The full details for the hill are:
Group: Moelwynion
Summit Height: 25.2m
(data via LIDAR)
Name: Bryn y Bont
OS 1:50,000 map: 115
Summit Grid Reference:
SH 59641 45973
Drop: 20.9m (data via
LIDAR)
My thanks to Aled Williams for sending the details of this
hill to me
Myrddyn Phillips (February 2018)
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