Mapping Mountains – Hill Reclassifications – The Welsh P15s and 200m Twmpau

Ffridd Cae Crydd (SN 749 976) – Welsh Sub-P15 reclassified to 200m Twmpau

There has been a reclassification to the list of The Welsh P15s and the 200m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis and a subsequent Trimble GeoXH 6000 survey conducted by Myrddyn Phillips. 

Ffridd Cae Crydd (SN 749 976)

The criteria for the two listings that this reclassification applies to are: 

The Welsh P15s – Welsh hills with 15m minimum drop, irrespective of their height, with an accompanying sub list entitled the Welsh Sub-P15s, with the criteria for this sub category being all Welsh hills with 14m or more and below 15m of drop.  The list is authored by Myrddyn Phillips, with the Introduction to the list appearing on Mapping Mountains on the 10^th May 2019. 

The Welsh P15s by Myrddyn Phillips

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 listed by is Ffridd Cae Crydd and it is adjoined to the Pumlumon group of hills, which are situated in the north-western part of Mid and West Wales (Region B, Sub-Region B2), and it is positioned with the A489 road to its north and minor roads to its west, south and east, and has the town of Machynlleth towards the north.

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

When the listing that became known as The Welsh P15s was being compiled, this hill was included in the P14 sub list with an estimated c 14m of drop, based on an estimated c 271m summit height and an estimated c 257m bwlch height, with both heights based on interpolation of 10m contouring that appear on the Ordnance Survey 1:25,000 Explorer map.  With an adjacent hill listed as Ffridd Eithaf (SN 745 977) given a summit height of 272m based on the spot height that appears on the contemporary Ordnance Survey 1:25,000 Explorer map. 

LIDAR image of Ffridd Cae Crydd (SN 749 976) on right and Ffridd Eithaf (SN 745 977) on left

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 Trimble GeoXH 6000 gathering data at the summit of Ffridd Cae Crydd with the summit of Ffridd Eithaf in the background

LIDAR analysis confirms Ffridd Cae Crydd as higher than Ffridd Eithaf, therefore their respective bylchau are swapped and as the summit of both hills have now been surveyed with the Trimble GeoXH 6000 it is this result that is being prioritised for listing purposes. 

The Trimble GeoXH 6000 survey result for each summit is given below:

 

Ffridd Cae Crydd:  272.289m at SN 74910 97692 

Ffridd Eithaf:  272.175m at SN 74578 97750 

 

Therefore, the confirmation of the reclassification of this hill from Welsh Sub-P15 status is due to LIDAR analysis and a subsequent Trimble GeoXH 6000 survey, resulting in a 272.3m summit height and a 232.8m bwlch height, with these values giving this hill 39.4m of drop, which is sufficient for it to be classified as a 200m Twmpau. 

 

The full details for the hill are: 

Group:  Pumlumon 

Name:  Ffridd Cae Crydd 

OS 1:50,000 map:  135

Summit Height:  272.3m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SN 74910 97692 (Trimble GeoXH 6000) 

Bwlch Height:  232.8m (LIDAR) 

Bwlch Grid Reference:  SN 75107 97628 (LIDAR) 

Drop:  39.4m (Trimble GeoXH 6000 summit and LIDAR bwlch) 

 

Myrddyn Phillips (October 2021)