Mapping Mountains – Hill Reclassifications – 30-99m Twmpau

Rhos Trebared (SN 173 475) – 30-99m Twmpau reclassified to 30-99m Sub-Twmpau 

There has been a reclassification to the list of 30-99m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived by LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Rhos Trebared (SN 173 475)

The criteria for the list that this reclassification 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, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

The 30-99m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Rhos Trebared and this was derived from local enquiry, and it is adjoined to the Mynydd Bach group of hills, which are situated in the western part of South Wales (Region B, Sub-Region B1), and it is positioned with the coast to its north-west, the B4548 road to its north-east and a minor road to its south, and has the town of Aberteifi (Cardigan) towards the south.

When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was included in the main P30 list.

When 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 30m of drop, based on the 69m summit spot height and the 39m bwlch spot height that appear on the Ordnance Survey 1:50,000 Landranger and 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 reclassification of this hill to 30-99m Sub-Twmpau status is due to LIDAR analysis, resulting in a 70.3m summit height and a 40.3m bwlch height, with these values giving this hill 29.9m of drop, which is insufficient for it to be classified as a 30-99m Twmpau. 

 

The full details for the hill are: 

Group:  Mynydd Bach 

Name:  Rhos Trebared 

OS 1:50,000 map:  145

Summit Height:  70.3m (LIDAR) 

Summit Grid Reference:  SN 17391 47521 (LIDAR)               

Bwlch Height:  40.3m (LIDAR) 

Bwlch Grid Reference:  SN 17728 47659 (LIDAR) 

Drop:  29.9m (LIDAR) 

 

Myrddyn Phillips (February 2023)