Broughton Burrows (SS
413 927)
There has been a Significant Height Revision to a hill that
is listed in the 30-99m Twmpau and Y Trechol – The Dominant Hills of Wales,
with the hill’s height, drop and dominance confirmed by LIDAR analysis
conducted by Myrddyn Phillips.
LIDAR image of Broughton Burrows |
The criteria for the two listings that this significant
height revision applies to are:
30-99m Twmpau – Welsh hills at or above
30m and below 100m in height that have a minimum 30m of 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.
Y Trechol – The Dominant Hills of Wales – Welsh P30 hills whose
prominence equal or exceed half that of their absolute height. With the criteria for Lesser Dominant status being those addition Welsh P30 hills whose
prominence is 33.33% or more and below 50% of their absolute height. The list is authored by Myrddyn Phillips with
the Introduction to the start of the Mapping Mountains publication of this list
appearing on the 3rd December 2015.
The name of the hill is Broughton Burrows, and it
is adjoined to the Gŵyr group of
hills, which are situated in the western part of South Wales (Region C, Sub-Region C1), and it is positioned at
the western end of the Gŵyr, and has the small community of Llangynydd towards
the south-east.
Although the summit of this hill is not a part of
open access land, and as such permission to visit should be sought, there is
general acceptance for people to visit, with the nearest public footpath encircling
the summit of the hill which comprises a dune system.
When the original Welsh 30-99m P30 list was
published on Geoff Crowder’s v-g.me website, this hill was listed with a 49m
summit height which appears as a spot height on the Ordnance Survey 1:25,000
Explorer map.
Extract from the Ordnance Survey 1:25,000 Explorer map |
When interpolated height and also drop values were
added to these lists, this hill was listed with c 32m of drop based on the 49m
spot height and an interpolated bwlch height of c 17m based on what was thought
to be bwlch contouring between 15m – 20m as indicated on the 1:25,000 Explorer
map. However, as this hill is a part of
a dune system this map did not show continuous contours on either the summit or
bwlch area of this hill.
Prior to LIDAR analysis this hill was analysed
using the 5m contouring on OS Maps, which is the recent replacement for OS
Get-a-map. The bwlch height was
confirmed as being between 15m – 20m and an interpolated height of c 18m the listed. However, this mapping showed a number of 60m
continuous ring contours for the summit area of this hill and therefore LIDAR
was examined, with the summit height produced being 61.9m and this comes within
the parameters of the Significant Height Revisions used within this page
heading, these parameters are:
Extract from OS Maps |
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 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.
Therefore, this hill’s new summit height is 61.9m
and this was produced from LIDAR analysis, this is 12.9m higher than its
previously listed height of 49m which appears as a spot height on the Ordnance
Survey 1:25,000 Explorer map, however this new height is in accordance with the
5m contouring on OS Maps.
LIDAR summit image of Broughton Burrows |
Close up LIDAR summit image of Broughton Burrows |
The full details for the hill are:
Group: Gŵyr
Name: Broughton
Burrows
OS 1:50,000 map: 159
Summit Height (New height):
61.9m (LIDAR)
Summit Grid Reference:
SS 41391 92781 (LIDAR)
Bwlch Height: 17.4m
(LIDAR)
Bwlch Grid Reference:
SS 41739 92663 (LIDAR)
Drop: 44.5m (LIDAR)
Dominance: 71.95%
(LIDAR)
Myrddyn Phillips (December 2018)
No comments:
Post a Comment