Mapping Mountains – Hill Reclassifications – 200m Twmpau

 

Cae Cefn (SN 547 121) – 200m Twmpau reclassified to 200m Sub-Twmpau

There has been a reclassification to the list of 200m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from detail produced by Joe Nuttall in his surface analysis programme, with subsequent LIDAR analysis conducted by the DoBIH team and independently by Myrddyn Phillips. 

LIDAR image of Cae Cefn (SN 547 121)

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

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 200m and below 300m 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 200m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Cae Cefn and this was derived from the Tithe map, 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 it is positioned with a minor road to its north and east, the B4310 road to its south-west and the A476 road to its south-east, and has the village of Cross Hands towards the east north-east.

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was listed as a twin top and included in the accompanying Hills to be surveyed sub list, as it was considered not to meet the criteria then used for the main P30 category.

When the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and its twin status split and it was listed with an estimated c 29m of drop, based on an estimated c 227m summit height and an estimated c 198m bwlch height, with both heights based on interpolation of 10m contouring that appear on the contemporary Ordnance Survey 1:25,000 Explorer map. 

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

Since the original publication of the Welsh P30 lists on Geoff Crowder’s v-g.me website there have been a number of maps made available online.  Some of these are historic such as the series of Six-Inch maps on the National Library of Scotland website.  Whilst others were digitally updated such as the Ordnance Survey Vector Map Local that was hosted on the Geograph website and which was entitled the Interactive Coverage Map, whilst others are current and digitally updated such as the interactive mapping on the Magic Maps and WalkLakes websites.

The details for this hill were re-assessed when the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map became available online.  This mapping had many spot heights not on other publicly available Ordnance Survey maps and for this hill it had a 227m summit spot height and with the bwlch height re-evaluated and the 197m spot height that appears on the contemporary Ordnance Survey 1:25,000 Explorer map taken as its height, these values gave this hill 30m of drop and therefore it was reclassified to 200m Twmpau status.

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.

Therefore, the reclassification of this hill to 200m Sub-Twmpau status is due to LIDAR analysis, resulting in a 226.5m summit height and a 196.8m bwlch height, with these values giving this hill 29.7m of drop, which is insufficient for it to be classified as a 200m Twmpau.

 

The full details for the hill are: 

Group:  Mynydd Sylen 

Name:  Cae Cefn 

OS 1:50,000 map:  159

Summit Height:  226.5m (LIDAR) 

Summit Grid Reference:  SN 54711 12139 (LIDAR) 

Bwlch Height:  196.8m (LIDAR) 

Bwlch Grid Reference:  SN 54478 11503 (LIDAR) 

Drop:  29.7m (LIDAR) 

 

Myrddyn Phillips (December 2023)