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

Lan Ddu Cilwenau (SN 572 371) 

There has been a Summit Relocation to a hill that is listed in the Y Trichant – The 300m Hills of Wales and Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop, dominance and status of the hill derived from detail on contemporary maps produced from Ordnance Survey data and LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Lan Ddu Cilwenau (SN 572 371)

The criteria for the two listings 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

Y Trechol – The Dominant Hills of Wales – Welsh P30 hills whose prominence equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height.  The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015, and the list is now available in its entirety on Mapping Mountains in Google Doc format. 

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Lan Ddu Cilwenau, 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 the B4337 road to its north-east, a minor road to its south-west and the B4310 road to its south-east, and has the village of Llansawel towards the east south-east.

When the original Welsh 300m P30 list was published on Geoff Crowder’s v-g.me website, this hill was listed with a 328m summit height, based on the spot height that is positioned at SN 57642 37049 and appears on the Ordnance Survey 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 summit image of Lan Ddu Cilwenau (SN 572 371)

The summit height produced by LIDAR analysis is 333.1m and is positioned at SN 57277 37147, and this 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 judged to be 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 333.1m and is positioned at SN 57277 37147, 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 400 metres eastward from where the previously listed summit is positioned. 

 

The full details for the hill are: 

Group:  Mynydd Pencarreg 

Name:  Lan Ddu Cilwenau 

OS 1:50,000 map:  146

Summit Height:  333.1m (LIDAR) 

Summit Grid Reference (New Position):  SN 57277 37147 (LIDAR) 

Bwlch Height:  c 211m (interpolation) 

Bwlch Grid Reference:  SN 56467 37617 (interpolation) 

Drop:  c 122m (LIDAR summit and interpolated bwlch) 

Dominance:  36.66% (LIDAR summit and interpolated bwlch) 

 

Myrddyn Phillips (May 2022)