Mapping Mountains – Hill Reclassifications – 200m Twmpau

Coed Ffridd Fawr (SH 869 033) – 200m Sub-Twmpau reclassified to 200m 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 initiated by Joe Nuttall who produced a summit analysis programme using LIDAR, and then by LIDAR analysis initially conducted by Jim Bloomer and subsequently by Myrddyn Phillips. 

LIDAR image of Coed Ffridd Fawr (SH 869 033)

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 Coed Ffridd Fawr and it is adjoined to the Carnedd Wen group of hills which are situated in the south-eastern part of North Wales (Region A, Sub-Region A4), and it is positioned with a minor road to its north and the A470 road to its south, and has the village of Llanbryn-mair towards the east south-east. 

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was included in the Hills to be surveyed sub list that accompanied the main P30 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-assessed and it was listed with an estimated c 29m of drop, based on the 242m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated c 213m bwlch height, based on interpolation of 10m contouring between 210m – 220m. 

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

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 214m spot height on the area of the bwlch, and when coupled with the 242m summit spot height these values gave this hill 28m of drop. 

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 from 200m Sub-Twmpau status is due to LIDAR analysis, resulting in a 244.0m summit height and a 213.5m bwlch height, with these values giving this hill 30.5m of drop, which is sufficient for it to be classified as a 200m Twmpau. 

 

The full details for the hill are: 

Group:  Carnedd Wen 

Name:  Coed Ffridd Fawr 

OS 1:50,000 map:  135, 136

Summit Height:  244.0m (LIDAR) 

Summit Grid Reference:  SH 86944 03372 (LIDAR) 

Bwlch Height:  213.5m (LIDAR) 

Bwlch Grid Reference:  SH 87416 03786 (LIDAR) 

Drop:  30.5m (LIDAR) 

 

Myrddyn Phillips (October 2021)