Mapping Mountains – Hill Reclassifications – 30-99m Twmpau

Pt. 85.8m (SS 748 953) – 30-99m Sub-Twmpau reclassified to 30-99m Twmpau

There has been confirmation of a reclassification to the list of 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. 85.8m (SS 748 953)

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. 85.8m) notation, and it is adjoined to the Cymoedd Morgannwg group of hills, which are situated in the central part of South Wales (Region C, Sub-Region C2), and it has the A474 road to its west and the B4287 road to its north-east, and has the town of Castell-nedd (Neath) towards its north.

This hill was included in the accompanying Hills to be surveyed sub list when the original Welsh 30-99m P30 hills were published on Geoff Crowder’s v-g.me website, as it did not meet the criteria then used for the main P30 list, however interpolated drop values and interpolated summit heights have now been included and the sub list has also been standardised.

When interpolated heights were used in this list this hill was listed with an estimated c 33m of drop, based on an estimated summit height of c 85m and an estimated bwlch height of c 52m, with both heights based on interpolation of 10m contouring on the Ordnance Survey 1:25,000 Explorer map.

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; this mapping is entitled the Interactive Coverage Map, and its larger scale and use of 5m contour intervals enabled a better judgement for the drop value of this hill and it was subsequently listed with an estimated c 34m 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 this hill’s reclassification to 30-99m Twmpau status is due to LIDAR analysis, resulting in an 85.8m summit height and a 53.4m bwlch height, with these values giving this hill 32.4m of drop.

The full details for the hill are:

Group:  Cymoedd Morgannwg

Name:  Pt. 85.8m

OS 1:50,000 map:  170

Summit Height:  85.8m (LIDAR)

Summit Grid Reference:  SS 74860 95395 (LIDAR)

Bwlch Height:  53.4m (LIDAR)

Bwlch Grid Reference:  SS 74976 95453 (LIDAR)

Drop:  32.4m (LIDAR)

Myrddyn Phillips (June 2019)