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

Wenvoe Quarry (ST 131 741)

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 and its position confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR summit image of Wenvoe Quarry (ST 131 741)

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 name the hill is now listed by is Wenvoe Quarry 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 a number of A roads encircling it with the A4232 to its north and east, the A4050 to its west and the A4055 further to its south-east, and has the city of Caerdydd (Cardiff) towards the north-east.

When the original Welsh 100m P30 list was published on Geoff Crowder’s v-g.me website this hill was listed with a c 115m summit height positioned at ST 132 742, based on the uppermost contour on contemporary Ordnance Survey 1:25,000 Explorer maps.

When this list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 117m summit height based on interpolation of the uppermost 115m contour on the Ordnance Survey 1:25,000 Explorer map, with this summit height later being changed to an estimated c 118m and with its summit position listed as ST 130 742.

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.

The height produced by LIDAR analysis is 123.4m and is positioned at ST 13189 74189, and 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 123.4m and this is positioned at ST 13189 74189, and this is approximately 130 metres south-eastward from where the estimated c 118m summit position was previously given.

The full details for the hill are:

Group:  Bro Morgannwg

Name:  Wenvoe Quarry

OS 1:50,000 map:  171

Summit Height:  123.4m (LIDAR)

Summit Grid Reference (New Position):  ST 13189 74189 (LIDAR)

Bwlch Height:  66m (spot height)

Bwlch Grid Reference:  ST 12669 74393 (spot height)

 

Drop:  57m (LIDAR summit and spot height bwlch)

Dominance:  46.51% (LIDAR summit and spot height bwlch)

Myrddyn Phillips (October 2019)