Crasty Frain (SO 109 983) – 200m Sub-Twmpau reclassified to
200m Twmpau
There has been confirmation of a reclassification
to the list of 200m Twmpau, with the summit height, bwlch height
and their locations, the drop and status of the hill initially confirmed by
LIDAR analysis instigated by Joe Nuttall who produced a summit analysis
programme, and then by LIDAR analysis conducted initially by Jim Bloomer and
subsequently by Myrddyn Phillips, with the summit later surveyed with the Trimble
GeoXH 6000 and which was conducted by Myrddyn Phillips.
Crasty Frain (SO 109 983) |
The criteria for the list that this
reclassification 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.
The 200m Twmpau by Myrddyn Phillips |
The name the hill is now listed by is Crasty Frain and this was derived from the Tithe map, and it is adjoined to the Carnedd Wen group of hills which are situated in the south-eastern part of North Wales (Region A, Sub-Region A4), and it is positioned with a minor road to its north and the B4389 road to its south-west, and has the village of Tregynon towards the west 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 included
in the accompanying Hills to be surveyed
sub list, as it was considered not to meet the criteria then used for the main
P30 list.
When the sub list was standardised, and
interpolated heights and drop values also included the details for this hill
were re-assessed and it was listed with an estimated c 27m of drop, based on
the 253m summit spot height that appears on the Ordnance Survey 1:25,000
Explorer map and an estimated c 226m bwlch height, with the latter based on
interpolation of 10m contouring between 220m – 230m.
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.
The reclassification of this hill was initiated by
Joe Nuttall who produced a summit analysis programme that used LIDAR with analternative height map (DEM) allowing identification of summits and cols and thereby drops. The resulting spreadsheet
that Joe produced contains over 29,600 hills.
LIDAR image of Crasty Frain |
This spreadsheet is being evaluated by a number of
people, and for this particular hill it was Jim Bloomer who initially assessed
this hill’s data against that produced via LIDAR. Myrddyn Phillips then evaluated the details
for this hill via LIDAR analysis and confirmed its height and drop and hence its
reclassification to 200m Twmpau status. The summit of this hill has now been surveyed
with the Trimble GeoXH 6000 and it is this evaluation on the hill and the
subsequent survey that is being prioritised.
The Trimble GeoXH 6000 gathering data at the summit of Crasty Frain |
Therefore, the confirmation of the
reclassification of this hill from 200m Sub-Twmpau status is due to LIDAR
analysis and a Trimble GeoXH 6000 survey, resulting in a 256.3m summit height
and a 226.1m bwlch height, with these values giving this hill 30.2m of drop,
which is sufficient for it to be classified as a 200m Twmpau.
The full details for the
hill are:
Group: Carnedd Wen
Name: Crasty Frain
OS 1:50,000 map: 136
Summit Height: 256.3m (converted to OSGM15, Trimble GeoXH
6000)
Summit Grid
Reference: SO 10995 98318 (Trimble GeoXH
6000)
Bwlch Height: 226.1m (LIDAR)
Bwlch Grid
Reference: SO 10787 98754 (LIDAR)
Drop: 30.2m (Trimble GeoXH 6000 summit and LIDAR
bwlch)
Myrddyn Phillips
(October 2020)
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