Tuesday, 24 March 2020

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

Coed Anghred Hill (SO 457 194)

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, dominance and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Coed Anghred Hill (SO 457 194)

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 3rd December 2015, and the list is now available in its entirety on Mapping Mountains in Google Doc format.

The name the hill is listed by is Coed Anghred Hill and it is adjoined to the Mynyddoedd Duon group of hills which are situated in the eastern part of South Wales (Region C, Sub-Region C3), and it is positioned with the Afon Mynwy (River Monnow) and the B4521 road to its north and the B4347 road to its west, and has the small village of Ynysgynwraidd (Skenfrith) 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 192m summit height based on the spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and which is positioned at SO 45823 19468.

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 Coed Anghred Hill

The summit height produced by LIDAR analysis is 198.8m positioned at SO 45713 19487.  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 it is positioned to a different feature such as in a conifer plantation, or when the high point of the hill is placed within a different map contour compared to its previous listed position, or 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 that is judged to be a relatively recent man-made construct.

Therefore, the summit height produced by LIDAR analysis is 198.8m and this is positioned at SO 45713 19487, this is approximately 110 metres westward from where the previously listed summit position was given to the 192m spot height.

The full details for the hill are:

Group:  Mynyddoedd Duon

Name:  Coed Anghred Hill

OS 1:50,000 map:  161

Summit Height:  198.8m (LIDAR)

Summit Grid Reference (new position):  SO 45713 19487 (LIDAR)

Bwlch Height:  128.8m (LIDAR)

Bwlch Grid Reference:  SO 44881 19181 (LIDAR)
Drop:  70.0m (LIDAR)

Dominance:  35.20% (LIDAR)

Myrddyn Phillips (March 2020)

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