Mapping Mountains – Summit Relocations – Y Trichant – The 300m Hills of Wales

Cwm Fron (SN 966 808) 

There has been a Summit Relocation to a hill that is listed in the 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 Cwm Fron (SN 966 808)

The criteria for the list that this summit relocation applies to:

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 13^th May 2017, and the Introduction to the Mapping Mountains publication of the list appearing on the 1^st January 2022. 

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

The name the hill is listed by is Cwm Fron, and it is adjoined to the Hirddywel group of hills, which are situated in the northern part of South Wales (Region B, Sub-Region B2), and it is positioned with the A470 road to its north-west, a minor road to its south-west and the B4518 road to its east, and has the town of Llanidloes towards the north.

When the original 300m 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 with a 379m summit height, based on the spot height positioned at SN 96621 81382 that appears on the Ordnance Survey 1:25,000 Exlorer map.  With the contemporary Ordnance Survey 1:50,000 Landranger map giving a 378m spot height positioned at SN 96642 80819. 

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

The details for this hill were re-assessed when the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map became available online.  This mapping had many spot heights not on other publicly available Ordnance Survey maps and for this hill it had a 379m summit spot height positioned at SN 96629 80855, this position is close to where the 379m spot height appears on the Ordnance Survey 1:50,000 Landranger map.  This resulted in the hill being listed with twin 379m summits. 

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 Cwm Fron (SN 966 808)

LIDAR analysis gives the highest ground on this hill as 377.7m positioned at SN 96629 80855, with LIDAR giving the northerly position as 377.5m positioned at SN 96704 81464, and this in relation to the originally listed summit position comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies when the high point of the hill is found to be positioned; in a different field, to a different feature such as in a conifer plantation,  within a different map contour either on Ordnance Survey maps or interactive mapping, to a different point where a number of potential summit positions are within close proximity, when natural ground or the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary or covered reservoir that is considered a relatively recent man-made construct, or a relocation of approximately 100 metres or more in distance from either the position of a map spot height or from where the summit of the hill was previously thought to exist.

Therefore, the summit height produced by LIDAR analysis is 377.7m and this is positioned at SN 96629 80855, this position is not given a spot height on the contemporary Ordnance Survey 1:25,000 Explorer map, and is approximately 610 metres southward from where the originally listed summit is positioned. 

 

The full details for the hill are:

Group:  Hirddywel 

Name:  Cwm Fron 

OS 1:50,000 map:  136

Summit Height:  377.7m (LIDAR)                                                           

Summit Grid Reference (New Position):  SN 96629 80855 (LIDAR) 

Bwlch Height:  318.2m (LIDAR) 

Bwlch Grid Reference:  SN 97301 81730 (LIDAR) 

Drop:  59.5m (LIDAR) 

 

Myrddyn Phillips (January 2025)