Twyn Croes Gwallter (SN
949 145)
There has been a Summit Relocation to a hill that
is listed in the Y Pedwarau – The 400m
Hills of Wales, with the summit height, bwlch height and their locations,
the drop and status of the hill confirmed by LIDAR analysis conducted by Aled
Williams.
 |
| LIDAR image of Twyn Croes Gwallter (SN 949 145) |
The criteria for the list that this summit
relocation 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 listed in 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.
The name the hill is listed
by is Twyn Croes Gwallter and it is adjoined
to the Fforest Fawr group of hills, which are situated in the western part of South
Wales (Region C, Sub-Region C2), and
it is positioned with the A470 road to its north north-east and the A4059 road
to its south-east, and has the town of Merthyr Tudful towards the south-east.
When the 1st edition of the Y Pedwarau was published by Europeaklist in May 2013 this hill was
listed with c 22m of drop based on the 458m summit height that appears as a
spot height positioned at SN 946 144 on the Ordnance Survey 1:25,000 Explorer
map and an estimated bwlch height of c 436m based on interpolation of 10m
contouring between 430m – 440m.
 |
| Extract from the Ordnance Survey 1:25,000 Explorer map |
When the Y
Pedwarau- The 400m Hills of Wales list was published on Mapping Mountains
the summit position for this hill was given as a ten figure grid reference of SN
94626 14403, based on the position of the spot height.
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 Twyn Croes Gwallter |
The summit height produced by LIDAR analysis is 456.6m
at SN 94995 14573, and this position in relation to that previously given comes within the
parameters of the Summit Relocations used within this page heading, these
parameters are:
The term Summit Relocations applies to any listed
hill whose summit meets the following criteria; where there are a number of
potential summit positions within close proximity and the highest point is not
where previously given, or a relocation of approximately 100 metres or more in
distance from either the position of a map spot height or from where the summit
of the hill was previously thought to exist, or when the summit of the hill is
in a different field compared to where previously given, or when it is
positioned to a different feature such as in a conifer plantation, or when the
high point of the hill is placed within a different map contour compared to its
previous listed position, or when natural ground or the natural and intact
summit of a hill is confirmed compared to a higher point such as a raised field
boundary that is judged to be a relatively recent man-made construct.
Therefore, the summit
height produced by LIDAR analysis for this hill is 456.6m and is positioned at
SN 94995 14573, this position is not given a spot height on contemporary
Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps and is
approximately 370 metres eastward from where the previously listed summit is
positioned.
The full details for the hill are:
Group: Fforest Fawr
Name: Twyn Croes Gwallter
OS 1:50,000 map: 160
Summit Height: 456.6m (LIDAR)
Summit Grid Reference (new position): SN 94995 14573 (LIDAR)
Bwlch Height: 434.5m (LIDAR)
Bwlch Grid Reference:
SN 95917 15369 (LIDAR)
Drop: 22.1m (LIDAR)
Aled Williams and Myrddyn Phillips (April 2020)
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