Mapping Mountains – Hill Reclassifications – 30-99m Twmpau

Warren Hill (SS 736 940) – 30-99m Twmpau addition

There has been confirmation of an addition to the list of 30-99m Twmpau, with the summit height, its location, the drop and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Warren Hill

The criteria for the list that this addition 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.

The name of the hill is Warren Hill 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 is encircled by major roads and a river with the A48 to its immediate north and the M4 to its immediate south and the Afon Nedd (River Neath) to its west, and has the town of Castell-nedd (Neath) towards its north.

This hill was not included in the original Welsh 30-99m height band of P30 hills published on Geoff Crowder’s v-g.me website, either in the main P30 or the Hills to be surveyed sub list, this was an oversight on my part as under the criteria used when this list was first compiled this hill qualified for the sub list.

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

The details for this hill were re-assessed after the sub list was standardised, and interpolated heights and drop values also included for the main P30 and the sub list, 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 enabled a better judgement for the drop value of this hill and it was subsequently included in the P30 list with an estimated c 31m 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. 

LIDAR summit image of Warren Hill

The confirmation of this hill’s addition to 30-99m Twmpau status is due to LIDAR analysis, resulting in a 44.5m summit height and a 13.2m bwlch height, with these values giving this hill 31.3m of drop.

The full details for the hill are:

Group:  Cymoedd Morgannwg

Name:  Warren Hill

OS 1:50,000 map:  170

Summit Height:  44.5m (LIDAR)

Summit Grid Reference:  SS 73667 94066 (LIDAR)

Bwlch Height:  13.2m (LIDAR)

Bwlch Grid Reference:  SS 73596 94201 (LIDAR)

Drop:  31.3m (LIDAR)

Myrddyn Phillips (May 2019)