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

The Beech (ST 346 974)

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 The Beech (ST 346 974)

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 The Beech and it is adjoined to the Cymoedd Gwent group of hills, which are situated in the eastern part of South Wales (Region C, Sub-Region C2), and it has a number of A roads encircling it with the A4042 to its west, the A472 to its north, the A449 to its east and the M4 motorway towards its south, and has the town of Brynbuga (Usk) towards its 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 184m summit height, based on the spot height positioned at ST 346 974 that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, with the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map positioning this spot height on the south-east side of a field boundary.

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 summit height produced by LIDAR analysis is 185.4m positioned at ST 34645 97459 with LIDAR also giving a 185.5m height positioned at ST 34663 97467 to the raised field boundary that is excluded from the height of this hill as it is considered a recent man-made construct.  Importantly the natural summit position of this hill is given by LIDAR to the north-west of the raised field boundary, and as such 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 185.4m to natural ground and this is positioned at ST 34645 97459, and although relatively close to where 184m spot height appears on the Ordnance Survey Vector Map Local hosted on the Geograph website, it is positioned in a different field from where the originally listed summit adjoined to this spot height is placed.

The full details for the hill are:

Group:  Cymoedd Gwent

Name:  The Beech

OS 1:50,000 map:  171

Summit Height:  185.4m (LIDAR, natural summit)

Summit Grid Reference (new position):  ST 34645 97459 (LIDAR, natural summit)

Bwlch Height:  89.0m (LIDAR)

Bwlch Grid Reference:  ST 34479 98091 (LIDAR)

 

Drop:  96.4m (LIDAR)

Dominance:  51.98% (LIDAR)

Myrddyn Phillips (September 2019)