Burry Holms (SS 398 926)
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, dominance and status confirmed by LIDAR analysis conducted
by Myrddyn Phillips.
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| LIDAR summit image of Burry Holms |
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 Burry Holms, and as this
name implies the hill is a part of an island, 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 is positioned at the western end of the Gŵyr, with the small community of
Llangynydd towards the east south-east.
Although the island 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 leading to the
beach and island to the east on the western part of Broughton Burrows.
When the original Welsh 30-99m P30 list was
published on Geoff Crowder’s v-g.me website this hill was listed with a 35m summit
height based on information from David Purchase who had noted a 35m spot height
on the Ordnance Survey 1:10,000 map.
Prior to LIDAR analysis the uppermost 30m ring
contour on contemporary Ordnance Survey maps had been interpolated, giving an estimated
summit height of c 33m. However, even
though the 1:10,000 mapping is prioritised over this interpolated summit
height, the 35.1m height produced by LIDAR analysis still comes within the
parameters of the Significant Height Revisions used within this page heading,
these parameters are:
 |
| Extract from the Ordnance Survey Interactive Coverage Map hosted on the Geograph website |
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 35.1m
and this was produced from LIDAR analysis, this height is only 0.1m higher than
the previously listed height of 35m which was derived from the Ordnance Survey
1:10,000 map, but it is 2.1m higher than the interpolated height of c 33m taken
from contemporary Ordnance Survey maps.
 |
| LIDAR bwlch image of Burry Holms |
The full details for the hill are:
Group: Gŵyr
Name: Burry Holms
OS 1:50,000 map: 159
Summit Height (New height):
35.1m (LIDAR)
Summit Grid Reference:
SS 39863 92603 (LIDAR)
Bwlch Height: 0.3m (LIDAR)
Bwlch Grid Reference:
SS 40173 92525 (LIDAR)
Drop: 34.8m (LIDAR)
Dominance: 99.02%
(LIDAR)
Myrddyn Phillips (December 2018)
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