Pt. 77.7m (ST 129 775) – 30-99m
Twmpau addition
There has been an addition to the list of 30-99m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips.
 |
| LIDAR image of Pt. 77.7m (ST 129 775) |
The criteria for the list that this addition
applies to are:
30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum
drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all
Welsh hills at or above 30m and below 100m 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.
As I do not know an appropriate name for this hill
either from historic research or local enquiry it is being listed by the point
(Pt. 77.7m) notation, and it is adjoined to the Cymoedd Morgannwg group of
hills, which are situated in the central
part of South Wales (Region C, Sub-Region C2), and it is encircled by minor roads with the Afon Elái (Ely River) to its south,
and is positioned on the edge of Fairwater which is a district in the west of
the city of Caerdydd (Cardiff).
This hill was not included in the main P30 list or
the accompanying Hills to be surveyed sub
list when the original Welsh 30-99m P30 hills were published on Geoff Crowder’s
v-g.me website, as it was considered not to meet the criteria then used for
this list. This list has now been
standardised with drop values and interpolated heights also included in the
main P30 and the accompanying sub list.
 |
| Extract from the Ordnance Survey 1:25,000 Explorer map showing the summit of this hill |
After this list was standardised with interpolated
heights and drop values also included the details for this hill were
re-assessed and it was listed with an estimated c 26m of drop, based on its 77m
summit spot height adjoined to a triangulation pillar that appears on the
Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and an estimated
bwlch height of c 51m based on interpolation of 5m contouring between 50m – 55m
on the Ordnance Survey 1:25,000 Explorer map.
However, this mapping shows that the critical bwlch of this hill could
be placed in one of two positions with the farthest position from its summit
now being part of land that forms a dismantled railway cutting.
 |
| Extract from the Ordnance Survey 1:25,000 Explorer map showing the bwlch of this hill |
The details for this hill were re-examined when
the OS Maps website became available online.
This is the replacement for OS Get-a-map and has contours at 5m
intervals and for the majority of land comprising old mine and quarry workings,
and rail and road cuttings it shows present day continuous contours, as opposed
to the broken contours on the 1:25,000 Explorer map. This map has bwlch contours for this hill
between 45m – 50m but its critical bwlch could still be placed in one of two
positions.
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 bwlch image of Pt. 77.7m |
The confirmation of this hill’s addition to 30-99m Twmpau status is due to LIDAR
analysis, resulting in a 77.7m summit height and a 44.4m bwlch height, with
these values giving this hill 33.3m of drop.
The inclusion of this hill to 30-99m Twmpau status is dependent upon using the height of rail or
road cuttings if lower on the hill to hill traverse in preference to the height
and position of any natural col that may still exist.
The full details for the hill are:
Group: Cymoedd
Morgannwg
Name: Pt. 77.7m
OS 1:50,000 map: 171
Summit Height: 77.7m
(LIDAR)
Summit Grid Reference:
ST
12931 77574 (LIDAR)
Bwlch Height:
44.4m (LIDAR)
Bwlch Grid Reference:
ST 11808 79174 (LIDAR)
Drop: 33.3m (LIDAR)
Myrddyn Phillips (August 2019)
No comments:
Post a Comment