Mapping Mountains – Hill Reclassifications – Y Trichant – The 300m Hills of Wales

Mynydd Fynnon Wen (SN 726 793) – Sub-Trichant reclassified to Trichant

There has been confirmation of a reclassification to the list of Y Trichant – The 300m Hills of Wales, 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 Mynydd Fynnon Wen (SN 726 793)

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

Y Trichant – The 300m Hills of Wales – Welsh hills at or above 300m and below 400m in height that have 30m minimum drop, with an accompanying sub list entitled the Sub-Trichant, with the criteria for this sub category being all Welsh hills at or above 300m and below 400m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the Introduction to the list and the renaming of it appearing on Mapping Mountains on the 13th May 2017.

Y Trichant - The 300m Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Mynydd Fynnon Wen 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 A44 road to its north and the A4120 road to its south and east, and has the village of Ponterwyd towards the east north-east.

When the original 300m height band of Welsh P30 hills was published on Geoff Crowder’s v-g.me website, this hill was included in the Hills to be surveyed sub list that accompanied the main P30 list, as it was considered not to meet the criteria then used for the main P30 category. 

Extract from the Ordnance Survey 1:50,000 Explorer map

When the P30 lists were standardised, and interpolated heights and drop values also included, this hill was listed with an estimated c 30m of drop based on the 376m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger map and an estimated c 346m bwlch height, based on interpolation of 10m contouring between 340m – 350m.  With its adjacent hill positioned at SN 724 797 listed with a 378m summit height based on the spot height 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.

Both summits have now been analysed via LIDAR.  The result produced by LIDAR analysis gives this hill a 376.4m summit height and as this is higher than the 375.8m adjacent summit positioned at SN 72420 79716, their respective bylchau are swapped.

Therefore, the confirmation of the reclassification of this hill from Sub-Trichant status is due to LIDAR analysis, resulting in a 376.4m summit height and a 333.4m bwlch height, with these values giving this hill 43.0m of drop, which is sufficient for it to be classified as a Trichant.

The full details for the hill are:

Group:  Pumlumon

Name:  Mynydd Fynnon Wen

OS 1:50,000 map:  135, 147

Summit Height:  376.4m (LIDAR)

                                                           

Summit Grid Reference:  SN 72691 79343 & SN 72693 79347 (LIDAR)

Bwlch Height:  333.4m (LIDAR)

Bwlch Grid Reference:  SN 72591 80115 (LIDAR)

Drop:  43.0m (LIDAR)

Myrddyn Phillips (December 2020)