Pen Twmp (SM 988 329) – Lesser Dominant
reclassified to Dominant
There has been a reclassification to the listing
of Y Trechol – The Dominant Hills of
Wales due to LIDAR analysis conducted by Myrddyn Phillips, with the criteria
for this list being:
Y Trechol – The Dominant Hills of Wales - Welsh P30 hills whose prominence equal or exceed
half that of their absolute height. With
an accompanying sub list entitled Y
Trechol - The Lesser Dominant Hills of Wales, with the criteria for this
sub category being those additional Welsh P30 hills whose prominence is 33% or
more and below 50% of their absolute height.
This hill was initially listed as a Dominant hill based on interpolation of
bwlch contours and later reclassified to Lesser
Dominant status based on the 109m spot height that appears on the area of
this hill’s bwlch on the Ordnance Survey Interactive Coverage Map hosted on the
Geograph website.
 |
| Extract from the Ordnance Survey Interactive Coverage Map hosted on the Geograph website |
A locally known name of the
hill is Pen Twmp and it is adjoined to the Mynydd Preseli group of hills, which are situated in the south-western
part of Mid and West Wales (Region B, Sub-Region B4). The hill is positioned with the A 40 road to
its west and the B 4313 road to its north and has the Nant y Bugail to its
south-west and the River Aer to its north-north-east, and has the town of
Abergwaun (Fishguard) towards the north-west.
If wanting to visit the hill
permission to do so should be sought as it is not a part of designated open
access land, for those wishing to do so a public footpath passes to the west of
the summit and can be accessed from either the north or south-west.
The reclassification of Pen Twmp to Dominant status is due to LIDAR bwlch analysis
conducted by Myrddyn Phillips. The LIDAR
(Light Detection & Ranging) technique produced highly accurate height data
that is now freely available for much of England and Wales.
The 2m DTM LIDAR analysis gives the hill the
following details:
Name: Pen
Twmp
Summit Height:
217m
Summit Grid Reference: SM 98820 32984
Bwlch Height:
108.3m
Bwlch Grid Reference: SM 99284 32968
Drop: 109m
Dominance:
50.09%
 |
| LIDAR image of Pen Twmp |
 |
| LIDAR image of the bwlch of Pen Twmp |
Therefore, the 217m summit spot height and the
108.3m LIDAR analysis for the bwlch position at SM 99284 32968 gives this hill
109m of drop and 50.09% Dominance, which is sufficient for it to be
reclassified to a Dominant hill.
The full details for the hill are:
Group: Mynydd Preseli
Name: Pen Twmp
Dominance: 50.09%
OS 1:50,000 map: 157
Summit Grid Reference:
SM 98820 32984
Summit Height: 217m
Drop Summit to Bwlch:
109m
Drop Bwlch
to ODN: 108.3m
Myrddyn Phillips (August 2018)
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