Bryn Llwyd (SO 108 825) – 400m Sub-Pedwar addition
There has been an addition to the listing of the Y Pedwarau – The 400m Hills of Wales, with
the summit height, bwlch height and their locations, the drop and status of the
hill derived from detail on contemporary Ordnance Survey maps.
This was initiated by Joe Nuttall who produced a
summit analysis programme that used LIDAR with an alternative height map (DEM)
allowing identification of summits and bylchau and thereby drops. The resulting spreadsheet that Joe produced
contains over 29,600 hills.
This spreadsheet is being evaluated by a number of
people, including Ronnie Bowron, who passed the details of this hill to us.
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 400m Sub-Pedwar category. The criteria for 400m Sub-Pedwar status being
all Welsh hills at or above 400m and below 500m 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.
 |
| Y Pedwarau - The 400m Hills of Wales by Myrddyn Phillips and Aled Williams |
The name the hill is listed by is Bryn Llwyd, and it is adjoined to the Beacon Hill
group of hills, which are situated
in the north-eastern part of Mid and West Wales (Region B, Sub-Region B1), and
it is positioned with a minor road to its south and east, and the A483 road to
its west and farther afield the B4355 road to its north-east, and has the town
of Y Drenewydd (Newtown) towards the north.
 |
| Extract from the Ordnance Survey 1:25,000 Explorer map |
When the 1st edition of the Y Pedwarau was published by Europeaklist
in May 2013, this hill was not included as it was listed with 19m of drop,
based on the 485m summit spot height that appears on the Ordnance Survey
1:25,000 Explorer map and the 466m spot height that appeared on a minor road on
the area of this hill’s bwlch on the Ordnance Survey Vector Map Local hosted on
the Geograph website and which is entitled the Interactive Coverage Map. This latter spot height also appears on the
Magic Map website.
 |
| Extract from the Magic Maps website |
With the summit analysis programme produced by Joe
Nuttall and the examination of its data by Ronnie Bowron, the details for this
hill have now been re-assessed against mapping on the OS Maps website. 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 being
listed with an estimated c 465m bwlch height based on interpolation of 5m
contouring between 460m – 465m, resulting in the drop value increasing to an
estimated c 20m.
 |
| Extract from the OS Maps website |
Therefore, the addition of this hill to 400m
Sub-Pedwar status is due to re-assessment of detail on contemporary Ordnance
Survey maps, resulting in a 485m summit height and an estimated c 465m bwlch
height, with these values giving this hill c 20m of drop which is sufficient
for it to be classified as a 400m Sub-Pedwar.
The full details for the hill are:
Group: Beacon Hill
Name: Bryn Llwyd
OS 1:50,000 map: 136
Summit Height: 485m
(spot height)
Summit Grid Reference:
SO 10859 82548 (spot height)
Bwlch Height: c 465 (interpolation)
Bwlch Grid
Reference: SO 11088 82983 (interpolation)
Drop: c 20m (spot
height 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 (September 2020)
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