Mapping Mountains – Summit Relocations – 200m Twmpau and Y Trechol – The Dominant Hills of Wales

 

Parc Lan Uchaf (SN 100 261) 

There has been a Summit Relocation to a hill that is listed in the 200m Twmpau 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 LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Parc Lan Uchaf (SN 100 261)

The criteria for the two listings that this summit relocation applies to are:

200m Twmpau - Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 200m and below 300m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

The 200m Twmpau 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 now listed by is Parc Lan Uchaf and this was derived from the Tithe map, and it is adjoined to the Mynydd Preseli 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 B4313 road to its west and minor roads to its south and east, and has the village of Maenclochog towards the north-west.When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was listed with a summit height of c 200m based on the uppermost contour that appears on the Ordnance Survey 1:25,000 Explorer map which is positioned at SN 100 260. 

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 Parc Lan Uchaf (SN 100 261)

LIDAR analysis gives the highest ground on this hill as 201.3m positioned at SN 10035 26167.  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.

The height produced by LIDAR analysis to the natural summit of this hill is 201.2m positioned at SN 10053 26179, 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 201.2m and this is to the natural summit of the hill which is positioned at SN 10053 26179, 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 20 metres north-eastward from where the high point of the raised field boundary is positioned. 

 

The full details for the hill are: 

Group:  Mynydd Preseli 

Name:  Parc Lan Uchaf 

OS 1:50,000 map:  145, 158

Summit Height:  201.2m (LIDAR) 

Summit Grid Reference (New Position):  SN 10053 26179 (LIDAR) 

Bwlch Height:  129.0m (LIDAR) 

Bwlch Grid Reference:  SN 09509 26745 (LIDAR) 

Drop:  72.2m (LIDAR) 

Dominance:  35.90% (LIDAR) 

 

Myrddyn Phillips (March 2023)