Mapping Mountains – Hill Reclassifications – 30-99m Twmpau

Pt. 65.9m (ST 352 947) – 30-99m Sub-Twmpau reclassified to 30-99m Twmpau

There has been confirmation of a reclassification to a hill listed in the 30-99m 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 Pt. 65.9m (ST 352 947)

The criteria for the list that this reclassification applies to are:

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m 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.

As I do not know an appropriate name for this hill either from historic research or local enquiry it is being listed by the point (Pt. 65.9m) notation, 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 is positioned with the A4042 road to the west and the A449 road to the east, and has the town of Caerllion (Caerleon) towards the south.

When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was included in the Hills to be surveyed sub list that accompanied the main P30 list, as it did not meet the criteria then used in 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-evaluated and it was listed with a 66m summit height based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated bwlch height of c 36m based on interpolation of 10m contouring between 30m – 40m, with these values giving this hill an estimated c 30m of drop.

Extract from the Ordnance Survey 1:25,000 Explorer map

The details for this hill were re-assessed when the Ordnance Survey Vector Map Local hosted on the Geograph website became available online; and which is entitled the Interactive Coverage Map.  This mapping has additional spot heights not available on any other form of Ordnance Survey publicly available map and in the case of this hill it has a bwlch spot height and 5m contouring.  The bwlch spot height is 33m and when coupled with the 66m summit spot height it gives this hill 33m of drop. 

Extract from the Ordnance Survey Vector Map Local hosted on the Geograph website

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 confirmation of the reclassification of this hill to 30-99m Twmpau status is due to LIDAR analysis, resulting in a 65.9m summit height and a 34.3m bwlch height, with these values giving this hill 31.6m of drop, which is sufficient for 30-99m Twmpau status. 

The full details for the hill are:

Group:  Cymoedd Gwent

Name:  Pt. 65.9m

OS 1:50,000 map:  171

Summit Height:  65.9m (LIDAR)

Summit Grid Reference:  ST 35225 94717 (LIDAR)

Bwlch Height:  34.3m (LIDAR)

Bwlch Grid Reference:  ST 35297 94949 (LIDAR)

Drop:  31.6m (LIDAR)

Myrddyn Phillips (September 2019)