Mapping Mountains – Hill Reclassifications – 200m Twmpau

Church Hill Common (SO 51785 10565 & SO 51788 10566) – 200m Sub-Twmpau reclassified to 200m Twmpau

There has been confirmation of a reclassification to the list of 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 reclassification 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 list entitled the 200m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 200m and below 300m 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.

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. 

When the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-assessed and it was listed with an estimated c 30m of drop, based on the 232m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated c 202m bwlch height, with the latter based on interpolation of 5m contouring between 200m – 205m.

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 image of Church Hill Common

The confirmation of the reclassification of this hill from 200m Sub-Twmpau status is due to LIDAR analysis, resulting in a 232.7m summit height and a 202.3m bwlch height, with these values giving this hill 30.3m of drop, which is sufficient for it to be classified as a 200m Twmpau.

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:  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 (May 2020)