Mapping Mountains – Hill Reclassifications – 200m Twmpau

Lan Fanal (SN 795 343) – 200m Sub-Twmpau reclassified to 200m Twmpau

There has been confirmation of a reclassification to the list of 200m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from detail produced by Joe Nuttall in his surface analysis progamme, with subsequent LIDAR analysis conducted by the DoBIH team and independently by Myrddyn Phillips. 

LIDAR image of Lan Fanal (SN 795 343)

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 Lan Fanal and this was derived from the Tithe map, and it is adjoined to the Mynydd Du group of hills, which are situated in the southern part of South Wales (Region B, Sub-Region B5), and it is positioned with the A40 road to its north and a minor road to its south-west, and has the town of Llanymddyfri (Llandovery) towards the west.

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 accompanying Hills to be surveyed sub 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-evaluated and it was listed with an estimated c 30m of drop, based on the 238m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated c 208m bwlch height, based on interpolation of 10m contouring between 200m – 210m. 

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. 

LIDAR summit image of Lan Fanal

LIDAR bwlch image of Lan Fanal

Therefore, the confirmation of the reclassification of this hill from 200m Sub-Twmpau status is due to LIDAR analysis, resulting in a 237.7m summit height and a 207.0m bwlch height, with these values giving this hill 30.7m of drop, which is sufficient for it to be classified as a 200m Twmpau.  With the bwlch height and position taken to natural ground at the base of a raised road whose critical point LIDAR gives as 207.6m in height and positioned at SN 79622 33060. 

 

The full details for the hill are: 

Group:  Mynydd Du 

Name:  Lan Fanal 

OS 1:50,000 map:  146, 160

Summit Height:  237.7m (LIDAR) 

Summit Grid Reference:  SN 79588 34329 (LIDAR) 

Bwlch Height:  207.0m (LIDAR) 

Bwlch Grid Reference:  SN 79626 33074 (LIDAR) 

Drop:  30.7m (LIDAR) 

 

Myrddyn Phillips (September 2023)