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

Cefn Penarth (SN 924 853) – Sub-Trichant reclassified to Trichant

There has been 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 initially confirmed by Joe Nuttall who produced a summit analysis programme using LIDAR, and then by LIDAR analysis initially conducted by Jim Bloomer and subsequently by Myrddyn Phillips, with the hill previously surveyed with the Trimble GeoXH 6000.

Cefn Penarth (SN 924 853)

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 now listed by is Cefn Penarth and this was derived from local enquiry, 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 between the river valleys of the Afon Clewedog to its north and the Afon Hafren (River Severn) to its south, and has a minor road running the length of its ridge and the B4518 road to its north-east, and has the town of Llanidloes towards the east south-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, as it was considered not to meet the criteria then used for the accompanying 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 29m of drop based on the 317m summit spot height and the 288m bwlch spot height that appear on the Ordnance Survey 1:25,000 Explorer map.

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

As the listed drop was close to the 30m minimum drop required for Trichant status this hill was prioritised for a GNSS survey, and this took place on the 20^th April 2014, resulting in 29.8m of drop.  However, since this hill was Trimbled, LIDAR is now available and the summit analysis undertaken by Joe Nuttall and LIDAR analysis conducted by Jim Bloomer prompted me to compare the Trimble result against the LIDAR.  The Trimble result is 0.07m lower for the summit compared to LIDAR, but with an approximate 16 metre difference in summit position and a 7 metre difference in bwlch position, the LIDAR result is being prioritised.

LIDAR image of Cefn Penarth

The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales and is revolutionising hill classification.

Therefore, the reclassification of this hill from Sub-Trichant status is due to LIDAR analysis, resulting in a 318.9m summit height and a 288.9m bwlch height, with these values giving this hill 30.0m of drop, which is sufficient for it to be classified as a Trichant.

The full details for the hill are:

Group:  Pumlumon

Name:  Cefn Penarth

OS 1:50,000 map:  136

Summit Height:  318.9m (LIDAR)

Summit Grid Reference:  SN 92419 85333 (LIDAR)

Bwlch Height:  288.9m (LIDAR)

Bwlch Grid Reference:  SN 92025 85612 (LIDAR)

Drop:  30.0m (LIDAR)

For details on the Trimble GeoXH 6000 survey of this hill

Myrddyn Phillips (October 2020)