Mapping Mountains – Hill Reclassifications – 100m Twmpau

Pedwar Erw (SS 864 837) – 100m Twmpau addition

There has been an addition of a hill to the 100m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Pedwar Erw

The criteria for the list that this addition applies to are:

100m Twmpau - Welsh hills at or above 100m and below 200m in height with 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 name of the enclosed land that once comprised ground where the summit of this hill is situated is Pedwar Erw, and this was derived from the Tithe map and it is this name that the hill is now listed by.  The hill is adjoined to the Cymoedd Morgannwg group of hills, which are situated in the central part of South Wales (Region C, Sub-Region C2), and it forms a part of landscaped ground that once made up the Margam opencast mine, and is encircled by minor roads to its north, west and east and has the B4281 road and the small communities of Cefn Cribwr and Kenfig Hill towards its south.

This hill did not appear in the original 100m height band of Welsh P30 hills when they were published on Geoff Crowder’s v-g.me website as contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps of the day showed the opencast mine without any ring contours of note.

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

This area was re-examined when the OS Maps website became available online.  This is the replacement for OS Get-a-map and has contours at 5m intervals and for the majority of land comprising old mine workings it shows present day contours, as opposed to the blank space showed on the counterparts of the 1:50,000 Landranger and 1:25,000 Explorer maps.

Extract from OS Maps

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. 

The addition of Pedwar Erw to 100m Twmpau status is due to analysis of data on the OS Maps website coupled with LIDAR analysis and inspection of imagery on Google Maps and Google Earth with the conclusion that this hill is solid and stable.  LIDAR analysis has resulted in a 131.0m summit height and a 98.4m bwlch height, with these values giving this hill 32.5m of drop, which is sufficient for this hill to be classified as a 100m Twmpau.

 

Extract from Google Maps

The full details for the hill are:

Group:  Cymoedd Morgannwg

Name:  Pedwar Erw

OS 1:50,000 map:  170

Summit Height:  131.0m (LIDAR)

Summit Grid Reference:  SS 86413 83767 (LIDAR)

Bwlch Height:  98.4m (LIDAR)

Bwlch Grid Reference:  SS 86635 84031 (LIDAR)

Drop:  32.5m (LIDAR)

Myrddyn Phillips (May 2019)