Yr Orsedd (SH 299 270) – 30–99m
Sub-Twmpau reclassified to 30-99m Twmpau
There has been confirmation of a Hill
Reclassification to the list of 30-99m
Twmpau, with the summit height, its location, the drop and status of the
hill confirmed by LIDAR analysis, and a subsequent summit survey with the
Trimble GeoXH 6000 conducted by Myrddyn Phillips, with the latter taking place
on the 3rd October 2018.
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| Yr Orsedd (SH 299 270) |
The criteria for the list that this reclassification applies
to are:
30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 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.
When the original Welsh P30 hills were published
on Geoff Crowder’s v-g.me website this hill appeared in the accompanying Hills to be surveyed sub list as it did
not meet the criteria then used for the main P30 list; however this sub list
has now been standardised with drop values and interpolated heights also
included in the main P30 and the accompanying sub list.
When this list was standardised with interpolated
heights and drop values included this hill was listed with c 31m of drop based
on the 64m summit spot height positioned at SH 295 266 on the Ordnance Survey
1:25,000 Explorer map and an estimated bwlch height of c 33m based on
interpolation of 10m bwlch contouring.
 |
| Extract from the Ordnance Survey 1:25,000 Explorer map |
The details for this hill were reassessed when the
Ordnance Survey Interactive Coverage Map hosted on the Geograph website became
available online, and this map has a 66m spot height at SH 299 270 which is adjoined
to the hill to the north-east, which only has an uppermost 60m ring contour on
the 1:25,000 Explorer map. Therefore the
summit position of the listed hill was relocated and its drop value increased
accordingly, with the Interactive Coverage Map also giving the south-westerly
hill a second 64m map heighted summit.
 |
| Extract from the Ordnance Survey Interactive Coverage Map hosted on the Geograph website |
Prior to the Trimble
GeoXH 6000 summit survey this hill and its adjoining south-westerly 64m twin map
heighted hill were analysed via LIDAR, and this confirmed that the
north-easterly summit is the higher.
The locally known name of the higher summit is Yr
Orsedd, whilst the lower south-westerly summit is known locally as Bryn Tŷ Newydd, and it is adjoined
to the Pen Llŷn group of
hills, which are situated in the western
part of North Wales (Region A, Sub-Region A1), and the hill is encircled by minor roads with the
coast to its south-west and east, and has the village of Abersoch towards its
north-east.
 |
| Bryn Tŷ Newydd, the old listed summit to the south-west |
As the summit of this hill is not a part of
designated open access land permission to visit should be sought, for those
wishing to do so the easiest approach is via the east using gates to access the
summit.
The confirmation of the reclassification of Yr
Orsedd to 30-99m Twmpau status is due
to LIDAR analysis and a summit survey with the Trimble GeoXH 6000 conducted by
Myrddyn Phillips, resulting in a 67.5m summit height and a 32.0m bwlch height,
with these values giving this hill 35.4m of drop which is sufficient for it to
be classified as a 30-99m Twmpau.
 |
| The Trimble GeoXH 6000 gathering data at the summit of Yr Orsedd |
The full details for the hill are:
Group: Pen Llŷn
Name: Yr Orsedd
OS 1:50,000 map: 123
Summit Height: 67.5m (converted
to OSGM15)
Summit Grid Reference:
SH 29952 27038
Bwlch Height: 32.0m (LIDAR)
Bwlch Grid Reference:
SH 29808 27337 (LIDAR)
Drop: 35.4m (Trimble
summit and LIDAR bwlch)
Myrddyn Phillips (February 2019)
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