Bryn y Fedwen (SJ 115 125) – 100m Sub-Twmpau addition
There has been confirmation of an addition to the list of 100m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis and a subsequent Trimble GeoXH 6000 survey conducted by Myrddyn Phillips.
LIDAR image of Bryn y Fedwen (SJ 115 125) |
100m Twmpau – Welsh hills at or above 100m and below 200m in height that have 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m 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.
The 100m Twmpau by Myrddyn Phillips |
When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was not included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category.
After 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 20m of drop, based on the 157m summit spot height and an estimated c 137m bwlch height, with the latter based on interpolation of 10m contouring between 130m – 140m that appear on the Ordnance Survey 1:25,000 Explorer map.
Extract from the Ordnance Survey 1:25,000 Explorer map |
LIDAR analysis confirms this hill as having over 20m of drop, but as this hill has now been surveyed with the Trimble GeoXH 6000 resulting in a 156.8m summit height, it is this result that is being prioritised for listing purposes.
The Trimble GeoXH 6000 gathering data at the summit of Bryn y Fedwen |
The full details for the hill are:
Group: Y Berwyn
Name: Bryn y Fedwen
OS 1:50,000 map: 125
Summit Height: 156.8m
(converted to OSGM15, Trimble GeoXH 6000)
Summit Grid Reference:
SJ
11582 12548 (Trimble GeoXH 6000)
Bwlch Height:
134.9m (LIDAR)
Bwlch Grid Reference:
SJ 11523 12758 (LIDAR)
Drop: 21.8m (Trimble GeoXH 6000 summit and LIDAR bwlch)
Myrddyn Phillips (July
2021)
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