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

 

Mynydd Llanfynydd (SN 545 286) 

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 Mynydd Llanfynydd (SN 545 286)

The criteria for the list that this summit relocation 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 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 now listed by is Mynydd Llanfynydd and this was derived from the Tithe map, and it is adjoined to the Mynydd Mallaen group of hills, which are situated in the central part of South Wales (Region B, Sub-Region B1), and it is positioned with minor roads to its west and east, and the B4310 road to its north-west, and has the village of Brechfa towards the north-west.

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 summit height of 325m that appears as a spot height adjoined to a triangulation pillar positioned at SN 54623 28570 that appears 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.

LIDAR analysis gives the highest ground on this hill as 326.1m positioned at SN 54584 28615.  However, this is a part of a raised field boundary and protocols dictate that as this is deemed a relatively recent man-made construct such ground is discounted from the height of a hill. 

LIDAR summit image of Mynydd Llanfynydd (SN 545 286)

The height produced by LIDAR analysis to the natural summit of this hill is 325.6m positioned at SN 54561 28617, and this position in relation to the raised field boundary 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, 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 325.6m and this is positioned at SN 54561 28617, this position is not given a spot height on the contemporary Ordnance Survey 1:50,000 Landranger and the 1:25,000 Explorer map, and is approximately 23 metres eastward from where the high point of the raised field boundary is positioned and approximately 65 metres north-westward from where the triangulation pillar is positioned. 

 

The full details for the hill are:

Group:  Mynydd Mallaen 

Name:  Mynydd Llanfynydd 

OS 1:50,000 map:  146

Summit Height:  325.6m (LIDAR)                                                           

Summit Grid Reference (New Position):  SN 54561 28617 (LIDAR) 

Bwlch Height:  245.05m (LIDAR) 

Bwlch Grid Reference:  SN 57145 30251 (LIDAR) 

Drop:  80.5m (LIDAR) 

 

Myrddyn Phillips (September 2023)