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

Cock Hill (ST 153 750)

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 image of Cock Hill (ST 153 750)

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 of the hill is Cock Hill 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 has the A4232 road to its north and east and a minor road towards its south, 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 153 750, based on the uppermost ring contour that appears on contemporary Ordnance Survey 1:25,000 Explorer maps which takes in a triangulation pillar with an adjoining flush bracket height of 115.345m positioned at ST 15338 75022.

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 no further details the summit location remained the same.

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 Cock Hill

The summit height produced by LIDAR analysis is 115.6m positioned at ST 15303 75089 with LIDAR also giving a 115.7m height positioned at ST 15310 75062 to a raised field boundary that is excluded from the height of this hill as it is considered a recent man-made construct and with the natural summit of the hill positioned in a different field compared to where the summit was originally listed.  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 115.6m to ground meeting the criteria used within this list and this is positioned at ST 15303 75089, this is in a different field to the previously listed summit position and is approximately 80 metres north-westward from it and approximately 28 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:  Cock Hill

OS 1:50,000 map:  171

Summit Height:  115.6m (LIDAR, natural summit)

Summit Grid Reference (new position):  ST 15303 75089 (LIDAR, natural summit)

Bwlch Height:  46.3m (LIDAR)

Bwlch Grid Reference:  ST 13392 74714 (LIDAR) 

Drop:  69.3m (LIDAR)

Dominance:  59.92% (LIDAR)

Myrddyn Phillips (September 2019)