Mapping Mountains – Hill Reclassifications – 30-99m Twmpau

Long Park (SS 072 984) – 30-99m Sub-Twmpau reclassified to 30-99m Twmpau

There has been a reclassification of a hill in the listing of 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 Long Park (SS 072 984)

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.

The name the hill is listed by is Long Park and this was derived from the Tithe map and it is adjoined to the Brandy Hill group of hills, which are situated in the south-western part of Mid and West Wales (Region B, Sub-Region B4), and is positioned with the coast to its south, the A4139 road to its north and the B4585 road to its west and south, and has the village of Maenorbŷr (Manorbier) towards the south-west.

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 was considered not to meet the criteria then used in the main P30 category. 

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 an estimated c 29m of drop based on an estimated c 80m summit height and an estimated bwlch height of c 51m, with both heights based on interpolation of 5m contouring that appears on Ordnance Survey 1:25,000 Explorer maps.

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 and which is entitled the Interactive Coverage Map became available online.  This mapping had many spot heights not on other publicly available Ordnance Survey maps.  As no additional information was shown on this mapping, the details for the hill remained the same.

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 bwlch image for Long Park

The reclassification of this hill from 30-99m Sub-Twmpau status is due to LIDAR analysis, resulting in a 79.2m summit height and a 48.0m bwlch height, with these values giving this hill 31.1m of drop which is sufficient for 30-99m Twmpau status.  With the 48.0m bwlch height taken to a railway cutting which meets the criteria used in this list.

The full details for the hill are:

Group:  Brandy Hill

Name:  Long Park

OS 1:50,000 map:  158

Summit Height:  79.2m (LIDAR)

Summit Grid Reference:  SS 07255 98449 (LIDAR)

Bwlch Height:  48.0m (LIDAR)

Bwlch Grid Reference:  SS 06985 99391 (LIDAR)

Drop:  31.1m (LIDAR)

Myrddyn Phillips (May 2020)