Crug Cwm (SN 612 257)
There has been a Summit Relocation to a hill that
is listed in the 100m Twmpau, with
the summit height, bwlch height and their locations, the drop and status of the
hill derived from detail
produced by Joe Nuttall in his surface analysis programme, with subsequent
LIDAR analysis conducted by the DoBIH team and independently by Myrddyn
Phillips.
|
LIDAR image of Crug Cwm (SN 612 257) |
The criteria for the list that this summit
relocation applies to are:
100m Twmpau - Welsh hills at or above 100m and below 200m in height that have 30m
minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau, with
the criteria for this sub category being all Welsh hills at or above 100m and
below 200m 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.
|
100m Twmpau by Myrddyn Phillips |
The name the hill is now listed by is Craig Cwm and
this was derived from the Tithe map, and it is adjoined to the Mynydd Mallaen
group of hills, which are situated in the central
part of South Wales (Region B, Sub-Region B1), and it is positioned encircled by minor roads, with
the A40 road farther to its south and the B4302 road farther to its east, and
has the town of Llandeilo towards the south south-east.
|
Extract from the Ordnance Survey 1:25,000 Explorer map |
After the sub list was standardised, and
interpolated heights and drop values also included the details for this hill
were re-evaluated and it was listed with an estimated c 34m of drop, based on
an estimated c 193m summit height positioned at SN 61434 26099, with the next
largest 190m ring contour estimated as c 192m positioned at SN 61257 25745, and
an estimated c 159m bwlch height, based on interpolation of 10m contouring
between 150m – 160m.
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 Crug Cwm (SN 612 257) |
LIDAR analysis gives the highest ground on this
hill as 192.8m positioned at SN 61260 25753, as opposed to 191.4m to the
previously listed summit positioned at SN 61430 26107 and SN 61432 26105, and
this comes within the
parameters of the Summit Relocations used within this page heading, these
parameters are:
The term Summit Relocations applies when the high
point of the hill is found to be positioned; in a different field, to a
different feature such as in a conifer plantation, within a different map contour, to a different
point where a number of potential summit positions are within close proximity,
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 or covered reservoir
that is judged to be a relatively recent man-made construct, 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.
Therefore, the height produced by LIDAR analysis to
the summit of this hill is 192.8m and is positioned at SN 61260 25753, this position is not
given a spot height on the contemporary Ordnance Survey 1:50,000 Landranger and
1:25,000 Explorer map, and is approximately 350 metres south-westward from
where the previously listed summit is positioned.
The full details for the
hill are:
Group: Mynydd Mallaen
Name: Crug Cwm
OS 1:50,000 map: 146
Summit Height: 192.8m (LIDAR)
Summit Grid Reference
(New Position): SN 61260 25753 (LIDAR)
Bwlch Height: 159.0m (LIDAR)
Bwlch Grid
Reference: SN 63103 27207 (LIDAR)
Drop: 33.8m (LIDAR)
Myrddyn Phillips
(February 2024)