Pt. 509.6m (SN 815 686) – 500m Double Sub-Pedwar addition
There has been an addition to the listing of the Y Pedwarau – The 400m Hills of Wales, with
the summit height and its location confirmed by LIDAR analysis conducted by
Aled Williams, and the bwlch height, its location, the drop and status of the
hill derived from detail on contemporary Ordnance Survey maps.
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| LIDAR image of Pt. 509.6m (SN 815 686) |
The criteria for the list that this addition applies
to are:
Y Pedwarau – The 400m Hills of Wales.
Welsh hills at or above 400m and below 500m in height that have 30m
minimum drop, accompanying the main Y Pedwarau list are five categories of sub
hills, with this hill being added to the 500m Double Sub-Pedwar category. The criteria for 500m Double Sub-Pedwar status
being all Welsh hills at or above 500m and below 510m in height that have 20m
or more and below 30m of drop. The list is co-authored by Myrddyn Phillips and Aled Williams and is published on Mapping Mountains in Google Doc format.
The hill is being listed by the point (Pt. 509.6m) notation, and
it is adjoined to the Elenydd group of hills, which
are situated in the northern part of Mid and West Wales (Region B, Sub-Region
B2), and is positioned with Llyn Teifi to its west south-west and the Claerwen
Reservoir to its south-east, and has the village of Pontrhydfendigaid towards
the west south-west.
When the original 400m 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
that accompanied the main P30 list, as only 400m sub hills were then a part of
this list.
When the 390m subs and latterly the 500m subs were
added to this list this hill was not included, as it was listed with a 510m
summit height based on the spot height that appears on the Ordnance Survey
1:50,000 Landranger and 1:25,000 Explorer map.
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| Extract from the Ordnance Survey 1:25,000 Explorer map |
The details for this hill were re-assessed when
the Ordnance Survey Vector Map Local hosted on the Geograph website and which
is entitled the Interactive Coverage Map became available online. This mapping had many spot heights not on
other publicly available Ordnance Survey maps.
The details for this hill were also 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 which are proving consistently more accurate
compared to the 5m contours that sometimes appear on Ordnance Survey 1:25,000
Explorer maps and used to appear on the online Vector Map Local. This re-assessment resulted in the hill
remaining listed with a 510m summit height and an estimated drop of c 21m.
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 summit image of Pt. 509.6m (SN 815 686) |
Therefore, the addition of this hill to 500m
Double Sub-Pedwar status is due to LIDAR summit analysis, resulting in a 509.6m
summit height and when coupled with the estimated c 489m bwlch height, these values
give this hill c 21m of drop which is sufficient for it to be classified as a
500m Double Sub-Pedwar.
The full details for the hill are:
Group: Elenydd
Name: Pt. 509.6m
OS 1:50,000 map: 135,
136, 147
Summit Height: 509.6m (LIDAR)
Summit Grid Reference:
SN 81513 68623 (LIDAR)
Bwlch Height: c 489m (interpolation)
Bwlch Grid
Reference: SN 81259 68985 (interpolation)
Drop: c 21m (LIDAR summit
and interpolated bwlch)
For the additions, reclassifications and deletions to Y Pedwarau – The 400m Hills of Wales reported
on Mapping Mountains since the May 2013 publication of the list by Europeaklist
please consult the following Change Registers:
Myrddyn Phillips and Aled Williams (February 2020)
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