Mapping Mountains – Summit Relocations – 30-99m Twmpau and Y Trechol – The Dominant Hills of Wales

 

Ffynnon Ellis (SN 392 204) 

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 from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Ffynnon Ellis (SN 392 204)

The criteria for the two listings that this summit relocation applies to are:

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

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 additional Welsh P30 hills whose prominence is between one third and half that 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 3^rd December 2015, and the list is now available in its entirety on Mapping Mountains in Google Doc format. 

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The name the hill is now listed by is Ffynnon Ellis and this was derived from the Tithe map, and it is adjoined to the Mynydd Pencarreg group of hills, which are situated in the south-western part of South Wales (Region B, Sub-Region B1), and it is positioned with a minor road to its north, and the B4312 and the A40 road to its south, and has the town of Caerfyrddin (Carmarthen) towards the immediate east.

When the original Welsh 30-99m P30 list was published on Geoff Crowder’s v-g.me website, this hill was listed with a summit height of 73m, based on the spot height that appears on the contemporary Ordnance Survey 1:25,000 Explorer map, which also indicates the presence of a covered reservoir. 

Extract from the Ordnance Survey 1:25,000 Explorer map

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR summit image of Ffynnon Ellis (SN 392 204)

LIDAR analysis gives a 73.7m height positioned at SN 39221 20463 to remaining natural ground close to the base of the elevated covered reservoir, the latter is discounted from the height of the hill as it is deemed a relatively recent man-made construct.  This position in relation to the covered reservoir comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies to when the high point is positioned in a different field, to a different feature such as a conifer plantation, within a different map contour, a different point where a number of potential summit positions are within close proximity, when natural ground or the natural and intact summit is confirmed compared to a higher point such as a raised field boundary or covered reservoir that is considered 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 73.7m and this is to the remaining natural summit of the hill which is positioned at SN 39221 20463, this position is given a spot height on the contemporary Ordnance Survey 1:25,000 Explorer map, and is approximately 2m lower that the high point of the covered reservoir. 

 

The full details for the hill are: 

Group:  Mynydd Pencarreg 

Name:  Ffynnon Ellis 

OS 1:50,000 map:  145, 159

Summit Height:  73.7m (LIDAR) 

Summit Grid Reference (New Position):  SN 39221 20463 (LIDAR) 

Bwlch Height:  33.8m (LIDAR) 

Bwlch Grid Reference:  SN 39997 20345 (LIDAR) 

Drop:  39.9m (LIDAR) 

Dominance:  54.09% (LIDAR) 

 

Myrddyn Phillips (September 2022)