Mapping Mountains – Summit Relocations – 100m Twmpau

Parc Ffynnon (SN 199 192 & SN 200 192) 

There has been a Summit Relocation to a hill that is listed in the 100m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Parc Ffynnon (SN 199 192 and SN 200 192)

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

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

The name the hill is now listed by is Parc Ffynnon and this was derived from the Tithe map, and it is adjoined to the Mynydd Preseli group of hills, which are situated in the south-western part of South Wales (Region B, Sub-Region B1), and it is positioned with minor roads to its west and east, and the A40 road to its south, and has the town of Hendy-gwyn ar Daf (Whitland) towards the south.

When the original Welsh 100m P30 list was published on Geoff Crowder’s v-g.me website, this hill was listed with an estimated c 145m summit height, based on interpolation of its uppermost 145m ring contour positioned at SN 20102 19284 that appears on the contemporary Ordnance Survey 1:25,000 Explorer map. 

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 analysis gives the highest ground on this hill as 143.7m positioned at SN 20028 19265.  However, this is a part of a raised field boundary and protocols dictate that as this is deemed a relatively recent man-made construct such ground is discounted from the height of a hill. 

LIDAR summit image of Parc Ffynnon (SN 199 192 and SN 200 192) 

The height produced by LIDAR analysis to the natural summit of this hill is 143.6m and is positioned at SN 19998 19263 and SN 20001 19261 and SN 20005 19264, 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 high point of the hill is found to be positioned; in a different field, to a different feature such as in a conifer plantation,  within a different map contour, to a different point where a number of potential summit positions are within close proximity, 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 or covered reservoir 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 height produced by LIDAR analysis to the natural summit of this hill is 143.6m and is positioned at SN 19998 19263 and SN 20001 19261 and SN 20005 19264, this position is not given a spot height on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, and is approximately 105 metres westward from where the uppermost 145m contour ring appears on the contemporary Ordnance Survey 1:25,000 Explorer map, and approximately 25 metres westward from where the high point of the raised field boundary is positioned.

 

The full details for the hill are: 

Group:  Mynydd Preseli 

Name:  Parc Ffynnon 

OS 1:50,000 map:  158

Summit Height:  143.6m (LIDAR) 

Summit Grid Reference (New Position):  SN 19998 19263 & SN 20001 19261 & SN 20005 19264 (LIDAR) 

Bwlch Height:  98.0m (LIDAR) 

Bwlch Grid Reference:  SN 19882 19602 & SN 19884 19603 (LIDAR) 

Drop:  45.6m (LIDAR) 

 

Myrddyn Phillips (June 2023)