Ynys Fach (SN 668 951)
There has been a Summit Relocation to a hill that is listed in the 30-99m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop, dominance and status of the hill derived 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 Fach (SN 668 951)|
30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 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|
|Y Trechol - The Dominant Hills of Wales 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.
After 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 34m summit height positioned at SN 670 948 and an estimated c 7m bwlch height, with both values based on interpolation of 10m contouring that appears on the Ordnance Survey 1:25,000 Explorer map, with 30m being the uppermost contour given the hill on this map.
|Extract from the Ordnance Survey 1:25,000 Explorer map|
The summit height produced by LIDAR analysis is 43.5m and is positioned at SN 66845 95141, and this comes within the parameters of the Summit Relocations used within this page heading, these parameters are:
The term Summit Relocations applies when the hill’s high point is found to be positioned; in a different field, to a different feature such as in a conifer plantation, placed within a different map contour, to a different point where a number of potential summit positions are within close proximity, or when natural ground or the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary that is judged to be a relatively recent man-made construct, or a relocation of approximately 100 metres or more in distance from either the position of a map spot height or from where the summit of the hill was previously thought to exist.
Therefore, the summit height produced by LIDAR analysis is 43.5m and this is positioned at SN 66845 95141, this position is not given a spot height on contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps, and is approximately 300 metres north north-westward from where the previously listed summit is positioned.
The full details for the hill are:
Name: Ynys Fach
OS 1:50,000 map: 135
Summit Height: 43.5m (LIDAR)
Summit Grid Reference (New Position): SN 66845 95141 (LIDAR)
Bwlch Height: 2.1m (LIDAR)
Bwlch Grid Reference: SN 67483 95096 (LIDAR)
Drop: 41.3m (LIDAR)
Dominance: 95.10% (LIDAR)
Myrddyn Phillips (April 2021)