Foel Lwyd (SH 720 723)
There has been a Significant Height Revision to a
hill that is listed in the Yr Uchafion
and 600m Twmpau, with the summit
height of the hill being confirmed by a Leica GS15 survey conducted by John
Barnard, Graham Jackson and Myrddyn Phillips on the 6th May 2013, and
subsequently surveyed along with the hill’s connecting bwlch by Alan Dawson
using a Leica RX 1250 and later surveyed by Myrddyn Phillips with a Trimble
GeoXH 6000 on the 31st August 2018.
Foel Lwyd (SH 720 723) |
The criteria for the two listings that this significant
height revision applies to are:
Yr Uchafion – Welsh hills at or above 500m in height that
have 15m minimum drop. The list is
co-authored by Myrddyn Phillips and Aled Williams, with the Introduction to
this list appearing on Mapping Mountains on the 4th November 2015.
600m Twmpau – Welsh hills at or above 600m and below 700m in
height that have 30m minimum drop, with an accompanying sub category entitled
the 600m Sub-Twmpau consisting of all
Welsh hills at or above 600m and below 700m in height that have 20m or more and
below 30m of drop. With the word Twmpau
being an acronym standing for thirty
welsh metre prominences and upward. The list is authored
by Myrddyn Phillips.
The name of the hill is Foel Lwyd, and it is
adjoined to the Carneddau range of hills, which are situated in the north-western
part of North Wales (Region A, Sub-Region A1), and it is positioned with the A
55 road to its north and the Afon Conwy and the A 470 road to its east, and has
the town of Penmaenmawr towards the north.
As the summit of the hill is a part of designated
open access land it can be approached from most directions, with access from
Bwlch y Ddeufaen towards the west south-west being the most convenient, the
hill can also be easily combined with its higher neighbour of Tal y Fan.
Prior to the survey with the Leica GS15 this hill
was listed with a 603m summit height, which was based on the spot height that
appears 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 |
The summit height produced by the Leica GS15 survey
is 600.2m, this is not a substantial height revision when compared to some
revised heights, but it does come within the parameters of the Significant
Height Revisions used within this page heading, these parameters are:
The term Significant Height Revisions applies to
any listed hill whose interpolated height and Ordnance Survey or Harvey map
summit spot height has a 2m or more discrepancy when compared to the survey
result produced by the Trimble GeoXH 6000 or any other GNSS receiver, or
analysis of data produced via LIDAR, also included are hills whose summit map
data is missing an uppermost ring contour when compared to the data produced by
the Trimble or by LIDAR analysis. As
heights on different scaled Ordnance Survey maps are not consistent the height
given on the 1:25,000 Explorer map is being prioritised in favour of the 1:50,000
Landranger map for detailing these revisions.
The Leica GS15 set-up position at the summit of Foel Lwyd |
The Trimble GeoXH 6000 set-up position at the summit of Foel Lwyd |
Therefore, this hill’s new summit height is 600.2m
and this was produced by surveying with the Leica GS15, this is 2.8m lower than
its previously listed height of 603m which appears as a spot height on the
Ordnance Survey Interactive Coverage Map hosted on the Geograph website.
The full details for the hill are:
Group: Carneddau
Name: Foel Lwyd
OS 1:50,000 map: 115
Summit Height (New height):
600.2m (converted to OSGM15) (Leica GS15)
Summit Grid Reference:
SH 72036 72323 (Leica GS15)
Bwlch Height: 546.8m (converted
to OSGM15) (Leica RX 1250)
Bwlch Grid Reference:
SH 72653 72316 (Leica RX 1250)
Drop: 53.3m (converted
to OSGM15) (Leica GS15 summit and Leica RX 1250 bwlch)
Myrddyn Phillips and Aled Williams (January 2019)
No comments:
Post a Comment