Mapping Mountains – Hill Reclassifications – 100m Twmpau

 

Cae Mawr (SN 462 175) and Safle Claddu Nant y Caws (SN 468 174) & (SN 469 174) – Dual Summit 100m Twmpau addition

There has been a Dual Summit addition to the list of 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 Cae Mawr (SN 462 175) and Safle Claddu Nant y Caws (SN 468 174 & SN 469 174)

The criteria for the list that this addition 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.  The list is authored by Myrddyn Phillips, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

100m Twmpau by Myrddyn Phillips

 

Dual Summit hills:

A hill classified as a Dual Summit is defined as one which has an extant natural summit coupled with that of a higher artificial summit, with the latter that can be described as stable in character.  In the main, these recent man-made constructions are the result of quarrying activities producing spoil tips, or as in this instance a landfill.  These recent man-made constructions are treated differently to ancient man-made constructions such as hill forts and tumuli, as if the latter are deemed stable and of an earthen character their age dictates that they can be viewed as being permanent in nature and are now effectively a part of the hill.  For those bagging Dual Summit hills, a visit to either the natural high point or the elevated man-made high point is sufficient to claim an ascent of the hill.  With the Dual Summit classification being a relatively new category and fist instigated in January 2018 for a Dual Summit Pedwar.

 

The name the hill is now listed by is Cae Mawr for the lower natural summit and Safle Claddu Nant y Caws for the higher man-made summit, and it is adjoined to the Mynydd Sylen group of hills, which are situated in the southern part of South Wales (Region B, Sub-Region B5), and the two summits are positioned with the A48 road to their north and a minor road to their south-west, and has the town of Caerfyrddin (Carmarthen) towards the north-west. 

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, the natural summit was included in the main P30 list with a 155m summit height, based on the spot height adjoined to a triangulation pillar positioned at SN 46405 17608 that appears on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map. 

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

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 then separated in to its two component parts, with the man-made summit listed with an estimated c 59m of drop, based on an estimated c 156m summit height and an estimated c 97m bwlch height, with both heights based on interpolation of 5m contouring that appeared on the interactive mapping hosted on the OS Maps website.  With the lower natural summit listed with a 155 summit height and the bwlch between these two summits estimated as c 138m, which if separating these hills would give an estimated c 17m of drop.

However, it was not until LIDAR became available that the details for these summits 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.

Therefore, the addition of this hill to Dual Summit 100m Twmpau status is due to LIDAR analysis, resulting in a 155.1m summit height for the natural summit and a 163.8m summit height for the man-made summit, and a 98.5m bwlch height, with these values giving the natural summit 56.6m of drop and the man-made summit 65.3m of drop, with the details for the higher summit prioritised within the list. 

 

The full details for the hill are:

Group:  Mynydd Sylen

Name:  Cae Mawr (natural Dual Summit) and Safle Claddu Nant y Caws (artificial Dual Summit)

OS 1:50,000 map:  159

Summit Height:  155.1m (natural Dual Summit) (LIDAR) and 163.8m (artificial Dual Summit (LIDAR)

Summit Grid Reference:  SN 46268 17566 (natural Dual Summit) (LIDAR) and SN 46899 17416 & SN 46900 17411 (artificial Dual Summit) (LIDAR)

Bwlch Height:  98.5m (LIDAR)

Bwlch Grid Reference:  SN 39491 11374 & SN 39493 11375 (LIDAR)

Drop:  56.6m (natural Dual Summit) (LIDAR) and 65.3m (artificial Dual Summit) (LIDAR)

 

Myrddyn Phillips (January 2025)