Ynys Dafydd (SH 646 134) – 30-99m Sub-Twmpau reclassified to 30-99m Twmpau
There has been a reclassification to the list of 30-99m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill initiated by Joe Nuttall who produced a summit analysis programme using LIDAR, and then by LIDAR analysis initially conducted by Jim Bloomer and subsequently by Myrddyn Phillips.
LIDAR image of Ynys Dafydd (SH 646 134) |
30-99m Twmpau – Welsh hills at or above 30m and below 100m in height that have 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.
The 30-99m Twmpau by Myrddyn Phillips |
When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was included in the Hills to be surveyed sub list that accompanied the main P30 list, as it was considered not to meet the criteria then used in the main P30 category.
When the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 27m of drop based on an estimated c 42m summit height and an estimated c 15m bwlch height, with both values based on interpolation of 10m contouring that appears on the Ordnance Survey 1:25,000 Explorer map.
Extract from the Ordnance Survey 1:25,000 Explorer map |
Therefore, the reclassification of this hill from 30-99m Sub-Twmpau status is due to LIDAR analysis, resulting in a 52.8m summit height and a 17.1m bwlch height, with these values giving this hill 35.7m of drop, which is sufficient for it to be classified as a 30-99m Twmpau.
The full details for the hill are:
Group: Rhinogydd
Name: Ynys Dafydd
OS 1:50,000 map: 124
Summit Height: 52.8m (LIDAR)
Summit Grid Reference: SH 64636 17484 (LIDAR)
Bwlch Height: 17.1m (LIDAR)
Bwlch Grid Reference: SH 64599 17744 (LIDAR)
Drop: 35.7m (LIDAR)
Myrddyn Phillips
(September 2021)
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