Mynydd Penygarreg (SH 815 818) – 30-99m Sub-Twmpau addition
There has been confirmation of an addition to the list of 30-99m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips.
LIDAR image of Mynydd Penygarreg (SH 815 818) |
The criteria for the list that this addition
applies to are:
30-99m
Twmpau – Welsh hills at or above 30m
and below 100m in height that have 30m minimum drop, with an accompanying sub list entitled the 30-99m
Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or
above 30m and below 100m 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.
30-99m Twmpau by Myrddyn Phillips |
The name the hill is listed by is Mynydd Penygarreg, and it is
adjoined to the Mynydd Hiraethog group of hills, which are situated in the northern part of North Wales (Region A,
Sub-Region A2), and it is positioned with the B5115
road to its immediate south-west, and has the town of Llandudno towards the west.
When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was not
included in the Hills to be surveyed
sub list, as it was considered not to meet the criteria then used for this sub
category.
After the sub list was standardised, and interpolated
heights and drop values also included the details for this hill were
re-evaluated and it was listed with an estimated c 21m of drop, based on an
estimated c 83m summit height and an estimated c 62m bwlch height, with both
heights based on interpolation of 5m contouring.
Extract from the Ordnance Survey 1:25,000 Explorer map |
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.
Therefore, the confirmation of the addition of
this hill to 30-99m Sub-Twmpau status is due to LIDAR analysis, resulting in an
83.9m summit height and a 61.6m bwlch height, with these values giving this
hill 22.4m of drop, which is sufficient for it to be classified as a 30-99m
Sub-Twmpau.
The full details for the hill are:
Group: Mynydd Hiraethog
Name: Mynydd Penygarreg
OS 1:50,000 map: 116
Summit Height: 83.9m (LIDAR)
Summit Grid Reference: SH 81597 81831 (LIDAR)
Bwlch Height: 61.6m (LIDAR)
Bwlch Grid Reference: SH 81599 81981 (LIDAR)
Drop: 22.4m (LIDAR)
Myrddyn Phillips (July 2024)
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