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

Mynydd y Garth (SN 711 081) 

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 y Garth (SN 711 081)

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 listed by is Mynydd y Garth 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 a minor road to its north and east, and the A474 road to its west, and has the town of Pontardawe towards the south. 

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

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 accompanying sub list with a 321m summit height, based on the spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and which is positioned at SN 71293 08388. 

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 Mynydd y Garth (SN 711 081)

LIDAR analysis gives the highest ground on this hill as 321.8m positioned at SN 71149 08116, and this in relation to the previously listed summit position which LIDAR analysis gives as 321.0m in height and positioned at SN 71306 08392 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 321.8m and this is positioned at SN 71149 08116, this position is not given a spot height on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, and is approximately 280 metres south south-westward from where the previously listed summit is positioned. 

 

The full details for the hill are:

Group:  Mynydd Du 

Name:  Mynydd y Garth 

OS 1:50,000 map:  160

Summit Height:  321.8m (LIDAR)                                                           

Summit Grid Reference (New Position):  SN 71149 08116 (LIDAR) 

Bwlch Height:  296.1m (LIDAR) 

Bwlch Grid Reference:  SN 71524 08760 (LIDAR) 

Drop:  25.7m (LIDAR) 

 

Myrddyn Phillips (March 2024)