Mapping Mountains – Summit Relocations – 200m Twmpau

Church Hill Common (SO 517 105)

There has been a Summit Relocation to a hill that is listed in the 200m Twmpau, 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 Church Hill Common (SO 517 105)

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

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub category entitled the 200m Sub-Twmpau consisting of all Welsh hills at or above 200m and below 300m in height that have 20m or more and below 30m of drop.  With the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

The name the hill is listed by is Church Hill Common, and it is adjoined to the Gwent Is Coed group of hills which are situated in the south-eastern part of South Wales (Region C, Sub-Region C3), and it is positioned with the B4293 road and the A40 road to the west and the A466 road and the Afon Gwy (River Wye) to the east, and has the town of Trefynwy (Mounmouth) towards the north-west.

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was included in the accompanying Hills to be surveyed sub list, as it was considered not to meet the criteria then used for the main P30 list, with its summit listed at SO 518 106 which compliments the position of the 232m spot height that appears on the Ordnance Survey 1:25,000 Explorer map.  

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.

LIDAR summit image of Church Hill Common (SO 517 105)

The summit height and position produced by LIDAR analysis is 232.7m at SO 51785 10565 and SO 51788 10566, and this position in relation to that previously given 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 new summit height for this hill is 232.7m and is positioned at SO 51785 10565 and SO 51788 10566, this position is not given a spot height on contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps and is approximately 60 metres southward and in a different part of enclosed land from where the previously listed summit is positioned. 

The full details for the hill are:

Group:  Gwent Is Coed

Name:  Church Hill Common

OS 1:50,000 map:  162

Summit Height:  232.7m (LIDAR)

Summit Grid Reference (new position):  SO 51785 10565 & SO 51788 10566 (LIDAR)

Bwlch Height:  202.3m (LIDAR)

Bwlch Grid Reference:  SO 51524 10349 (LIDAR)

Drop:  30.3m (LIDAR)

Myrddyn Phillips (June 2020)