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

Crug y Gorllwyn (SN 321 340) 

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 Crug y Gorllwyn (SN 321 340)

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 Crug y Gorllwyn, and it is adjoined to the Mynydd Pencarreg group of hills, which are situated in the south-western part of South Wales (Region B, Sub-Region B1), and it is positioned with minor roads to its north, west and south, and the B4333 road to its east, and has the town of Castell Newydd Emlyn (Newcastle Emlyn) 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 Hills to be surveyed sub list with a summit height of 326m, based on the spot height adjoined to a triangulation pillar positioned at SN 32185 34085 that appears on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map. 

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

After 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 28m of drop, based on the 326m summit spot height and the 298m bwlch spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage 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 327.5m positioned at SN 32249 34121 and SN 32258 34125.  However, this is a part of a covered reservoir 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 Crug y Gorllwyn (SN 321 340)

The height produced by LIDAR analysis to the summit of this hill is 326.2m positioned at SN 32186 34079, and this position in relation to covered reservoir 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 326.2m and this is positioned at SN 32186 34079, this position is beside the triangulation pillar and is approximately 63 metres south-westward from the high point of the covered reservoir. 

 

The full details for the hill are:

Group:  Mynydd Pencarreg 

Name:  Crug y Gorllwyn 

OS 1:50,000 map:  145

Summit Height:  326.2m (LIDAR)                                                           

Summit Grid Reference (New Position):  SN 32186 34079 (LIDAR)                                        

Bwlch Height:  297.1m (LIDAR) 

Bwlch Grid Reference:  SN 32843 35432 (LIDAR) 

Drop:  29.1m (LIDAR) 

 

Myrddyn Phillips (May 2024)