Foel Penolau (SH 661 347 and SH 661 348) – 600m
Sub-Twmpau reclassified to 600m Twmpau
There has been a reclassification to a hill that
is listed in the 600m Twmpau, with
the summit height, bwlch height and their locations, the drop and status of the
hill confirmed by a survey with the Trimble GeoXH 6000 which was conducted over
two days by Myrddyn Phillips and Aled Williams on the 17th November
2018 and by Myrddyn Phillips on the 26th November 2018.
 |
| Foel Penolau (SH 661 347 and SH 661 348) |
The criteria for the list that this hill
reclassification applies to are:
600m Twmpau – Welsh hills at or above 600m and below 700m in
height that have 30m minimum drop, with an accompanying sub category entitled
the 600m Sub-Twmpau consisting of all
Welsh hills at or above 600m and below 700m in height that have 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 Foel Penolau and it is
adjoined to the Rhinogydd group of hills, which are situated in the western
part of North Wales (Region A, Sub-Region A1), and it is positioned with the A496
road to the west and the A470 road and the village of Trawsfynydd towards the
east.
When the list that later became known as the 600m Twmpau was first compiled this hill
was listed with c 26m of drop based on the 614m summit spot height that appears
on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps and an
estimated bwlch height of c 588m based on interpolation of 10m contouring
between 580m – 590m.
 |
| Extract from the Ordnance Survey 1:25,000 Explorer map |
The details for this hill were re-evaluated when
the Ordnance Survey Vector Map Local became available online; this map is
hosted on the Geograph website and is entitled the Interactive Coverage Map. As well as showing twin 614m map heighted
summits it also gave a 588m spot height in the area of this hill’s bwlch, but
as lower ground was known to exist on the hill to hill traverse compared to
where this spot height is positioned the drop value was amended to an estimated
c 27m.
 |
| Extract from the Ordnance Survey Vector Map Local hosted on the Geograph website |
This hill’s details were again re-assessed when
the OS Maps website became available online.
This is the replacement for OS Get-a-map and has contours at 5m
intervals and these showed that the 588m spot height that appears on the
Ordnance Survey Vector Map Local is not positioned at the critical bwlch of
this hill. These contours placed the position
of the critical bwlch in the boulder field below this hill’s eastern face and resulted
in an estimated c 30m of drop, based on an estimated c 584m bwlch height based
on interpolation of contours between 580m – 585m and the 614m spot height given
to the two twin map heighted summits.
 |
| Extract from the OS Maps website |
The confirmation of the reclassification of Foel
Penolau to 600m Twmpau status is due
to a survey with the Trimble GeoXH 6000 resulting in a 614.4m summit height
(with 1mm difference between the northern and southern summits the Trimble was
unable to split these tops) and a 582.5m bwlch height, with these values giving
this hill 31.9m of drop which is sufficient for it to be classified as a 600m Twmpau.
 |
| The Trimble set-up position at the northerly summit of Foel Penolau |
 |
| The Trimble set-up position at the critical bwlch of Foel Penolau |
The full details for the hill are:
Group: Rhinogydd
Name: Foel Penolau
OS 1:50,000 map: 124
Summit Height: 614.4m (converted
to OSGM15)
Summit Grid Reference:
SH
66184 34832 and SH 66145 34774
Bwlch Height: 582.5m (converted to OSGM15)
Bwlch Grid Reference: SH 66099 34735
Drop: 31.9m
Myrddyn Phillips (May 2019)
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