Mapping Mountains – Hill Reclassifications – 100m Twmpau

Ffridd Uchaf (SH 799 668) – 100m Sub-Twmpau addition

There has been confirmation of an addition to the list of 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 Ffridd Uchaf (SH 799 668)

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

The name the hill is now listed by is Ffridd Uchaf, and this was derived from the Tithe map, and it is adjoined to the Mynydd Hiraethog group of hills, which are situated in the northern part of North Wales (Region A, Sub-Region A1), and it is positioned encircled by minor roads with the A470 road farther to its west, and has the town of Llanrwst towards the south.

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was not included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category.

After 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 27m of drop, based on the 182m summit spot height and the 155m bwlch spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map. 

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

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 confirmation of the addition of this hill to 100m Sub-Twmpau status is due to LIDAR analysis, resulting in a 182.4m summit height and a 155.8m bwlch height, with these values giving this hill 26.6m of drop, which is sufficient for it to be classified as a 100m Sub-Twmpau. 

 

The full details for the hill are: 

Group:  Mynydd Hiraethog 

Name:  Ffridd Uchaf 

OS 1:50,000 map:  115

Summit Height:  182.4m (LIDAR) 

Summit Grid Reference:  SH 79916 66826 & SH 79918 66824 (LIDAR) 

Bwlch Height:  155.8m (LIDAR) 

Bwlch Grid Reference:  SH 79340 66846 (LIDAR) 

Drop:  26.6m (LIDAR) 

 

Myrddyn Phillips (August 2026)