Mapping Mountains – Hill Reclassifications – 30-99m Twmpau

Trwyn y Tal (SH 366 471) – 30-99m Sub-Twmpau addition 

There has been confirmation of an addition to the list of 30-99m 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 Trwyn y Tal (SH 366 471)

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

30-99m Twmpau – Welsh hills at or above 30m and below 100m in height that have 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 30m and below 100m 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. 

30-99m Twmpau by Myrddyn Phillips

The name the hill is listed by is Trwyn y Tal, and it is adjoined to the Yr Eifl group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with minor roads to its south-east, and the B4417 road farther to its south and the A499 road farther to its east, and has the small community of Trefor towards the south-east.

When the original 30-99m 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-evaluated and it was listed with an estimated c 24m of drop, based on an estimated c 52m summit height and an estimated c 28m bwlch height, with both heights based on interpolation of 10m contouring that appears on the Ordnance Survey 1:25,000 Explorer 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 30-99m Sub-Twmpau status is due to LIDAR analysis, resulting in a 51.8m summit height and a 25.6m bwlch height, with these values giving this hill 26.2m of drop, which is sufficient for it to be classified as a 30-99m Sub-Twmpau. 

 

The full details for the hill are: 

Group:  Yr Eifl 

Name:  Trwyn y Tal 

OS 1:50,000 map:  123

Summit Height:  51.8m (LIDAR) 

Summit Grid Reference:  SH 36684 47142 & SH 36685 47143 (LIDAR)               

Bwlch Height:  25.6m (LIDAR) 

Bwlch Grid Reference:  SH 36604 46908 (LIDAR) 

Drop:  26.2m (LIDAR) 

 

Myrddyn Phillips (September 2025)