Grug (SN 441 328)
There has been a Summit Relocation to a hill that is listed in the 200m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips.
LIDAR image of Grug (SN 441 328) |
The criteria for the list that this summit
relocation applies to are:
200m Twmpau - Welsh hills at or above 200m and below 300m in height that have 30m
minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau, with
the criteria for this sub category being all Welsh hills at or above 200m and
below 300m 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.
200m Twmpau by Myrddyn Phillips |
The name the hill is now listed by is Grug and
this was derived from the Tithe map, and it is adjoined to the Mynydd Pencarreg
group of hills, which are situated in the
south-western part of South Wales (Region B, Sub-Region B1), and it is positioned with a minor road to its north
and south-east, and the A485 road to its east, and has the town of Llandysul towards
the north north-west.
When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was not
included in the accompanying Hills to be
surveyed sub list, as it was considered not to meet the criteria then used
for this sub category.
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 25m of drop, based on the 266m summit
spot height positioned on a road at SN 44142 32904 that appears on the
contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and the
241m bwlch spot height that appeared on the Ordnance Survey Vector Map Local
hosted on the Geograph website and which was entitled the Interactive Coverage
Map.
Extract from the Ordnance Survey 1:25,000 Explorer map |
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 analysis gives the highest ground on this
hill as 267.4m positioned at SN 44163 32897.
However, this is on the edge of a raised road and protocols dictate that
as this is deemed a relatively recent man-made construct such ground is
discounted from the height of a hill.
LIDAR summit image of Grug (SN 441 328) |
The height produced by LIDAR analysis to the
natural summit of this hill is 266.6m and this is positioned at SN 44127 32866,
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 considered 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 summit
height produced by LIDAR analysis is 266.6m and this is positioned at SN 44127
32866, 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 38 metres south-westward from the previously listed
summit position and the high point of the raised road.
The full details for the hill are:
Group: Mynydd Pencarreg
Name: Grug
OS 1:50,000 map: 146
Summit Height: 266.6m (LIDAR)
Summit Grid Reference (New Position): SN 44127 32866 (LIDAR)
Bwlch Height: 240.6m (LIDAR)
Bwlch Grid Reference: SN 45100 33058 (LIDAR)
Drop: 26.0m (LIDAR)
Myrddyn Phillips
(October 2024)
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