Mapping Mountains – Summit Relocations – 100m Twmpau and Y Trechol – The Dominant Hills of Wales

Pt. 103.2m (SS 923 719)

There has been a Summit Relocation to a hill that is listed in the 100m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR summit image of Pt. 103.2m (SS 923 719)

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

100m Twmpau - Welsh hills at or above 100m and below 200m in height with 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m 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.

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.

The hill is being listed by the Point (Pt. 103.2m) notation as I do not know an appropriate name for it either from historic research or local enquiry, and it is adjoined to the Bro Morgannwg group of hills, which are situated in the southern part of South Wales (Region C, Sub-Region C2), and it is positioned with the B4265 to its north-east and minor roads to its north and west, and has the small community of Y Wig (Wick) towards the north.

When the original Welsh 100m P30 list was published on Geoff Crowder’s v-g.me website this hill was listed with a 102m summit height, based on the spot height positioned at SS 921 719 that appears on the Ordnance Survey 1:25,000 Explorer map.

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

The details for this hill were re-evaluated when the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map became available online, and as this map gives a 103m spot height positioned at SS 92333 71971, the summit of this hill was relocated.

Extract from the Ordnance Survey Vector Map Local hosted on the Geograph website

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.

Close up LIDAR summit image of Pt. 103.2m (SS 923 719)

The summit height produced by LIDAR analysis is 103.2m positioned at SS 92366 71993 with LIDAR also giving a 103.4m height positioned at SS 92370 72054 to a raised field boundary that is excluded from the height of this hill as it is considered a recent man-made construct.  The above detail comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies to any listed hill whose summit meets the following criteria; where there are a number of potential summit positions within close proximity and the highest point is not where previously given, 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, or when the summit of the hill is in a different field compared to where previously given, or when the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary that is judged to be a relatively recent man-made construct.

Therefore, the summit height produced by LIDAR analysis is 103.2m to ground meeting the criteria used within this list and this is positioned at SS 92366 71993, this is relatively close to where the 103m spot height appears on the Ordnance Survey Vector Map Local hosted on the Geograph website and is positioned approximately 170 metres east north-eastward from where the 102m spot height appears on the Ordnance Survey 1:25,000 Explorer map and approximately 60 metres from where the highest part of the raised field boundary is situated, and as the latter is considered a relatively recent man-made construct it is not taken as a part of the height of this hill.

The full details for the hill are:

Group:  Bro Morgannwg

Name:  Pt. 103.2m

OS 1:50,000 map:  170

Summit Height:  103.2m (LIDAR, natural summit)

Summit Grid Reference (new position):  SS 92366 71993 (LIDAR, natural summit)

Bwlch Height:  59.4m (LIDAR)

Bwlch Grid Reference:  SS 97154 74620 & SS 97156 74616 & SS 97158 74613 (LIDAR)

 

Drop:  43.8m (LIDAR)

Dominance:  42.43% (LIDAR)

Myrddyn Phillips (September 2019)