Mapping Mountains – Summit Relocations – 100m Twmpau

Pt. 143.7m (ST 330 982) 

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 Pt. 143.7m (ST 330 982)

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. 

100m Twmpau by Myrddyn Phillips

The hill is now listed by the point (Pt. 143.7m) notation, and it is adjoined to the Cefn yr Ystrad group of hills, which are situated in the southern part of South Wales (Region B, Sub-Region B5), and it is positioned with minor roads to its north and south-east, and the A4042 road to its west, and has the town of Pont-y-pŵl (Pontypool) towards the west north-west.

When the original Welsh 100m P30 list was published on Geoff Crowder’s v-g.me website, this hill was listed with a 142m summit height, based on the spot height positioned at ST 332 984 that appears on the 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 summit image of Pt. 143.7m (ST 330 982)

LIDAR analysis gives the highest ground on this hill as 143.7m positioned at ST 33080 98268.  With LIDAR giving the originally listed summit as 143.3m positioned at ST 33256 98508, 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 either on Ordnance Survey maps or interactive mapping, 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 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 height produced by LIDAR analysis to the summit of this hill is 143.7m and is positioned at ST 33080 98268, this is approximately 240 metres south-westward and positioned in a different map contour from where the originally listed summit is positioned. 

 

The full details for the hill are: 

Group:  Cefn yr Ystrad 

Name:  Pt. 143.7m 

OS 1:50,000 map:  171

Summit Height:  143.7m (LIDAR) 

Summit Grid Reference (New Position):  ST 33080 98268 (LIDAR) 

Bwlch Height:  119.3m (LIDAR) 

Bwlch Grid Reference:  ST 33629 99205 (LIDAR) 

Drop:  24.4m (LIDAR) 

 

Myrddyn Phillips (February 2025)