Mapping Mountains – Hill Reclassifications – 100m Twmpau

Goetre Coed (ST 091 965) – 100m Twmpau addition

There has been an addition of a hill to the listing of 100m Twmpau, with the summit height and its location, the drop and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Goetre Coed (ST 091 965)

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

100m Twmpau - Welsh hills at or above 100m and below 200m in height with 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m 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 bounded land where the summit of this hill is situated is Goetre Coed, and this was derived from the Tithe map and it is the name that this hill is now listed by.  The hill is adjoined to the Fforest Fawr group of hills, which are situated in the northern part of South Wales (Region C, Sub-Region C2), and it is almost encircled by the Afon Taf (River Taff) with only its south-western side free from the river, and is positioned with the A470 road to its south-west and the A4054 road to its north-east, and has the small town of Treharris to its north-east.

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was not included in either the main P30 list or the accompanying Hills to be surveyed sub list as it was thought not to have sufficient drop to be a listed as a P30 and it was also thought not to meet the criteria then used for the sub-list.

When this list was standardised and interpolated heights and drop values also included, the details for the hill were re-assessed, but as the bwlch of the hill has a rail and road cutting the contours are not continuous on the Ordnance Survey 1:25,000 Explorer map, therefore its drop value was difficult to estimate and it remained unlisted.

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

The details for this hill were next re-assessed when the 5m contouring on OSMaps became available online, and as this mapping had continuous contours on the area of this hill’s bwlch an estimated c 40m drop value could be given to the hill, based on its 166m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated bwlch height of c 128m based on interpolation of 5m contouring between 125m – 130m.

Extract from OSMaps

However, it was not until LIDAR became available and analysed 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 Goetre Coed

The summit height produced by LIDAR analysis is 165.9m and is positioned at ST 09189 96517, and the bwlch height is 125.8m and is positioned at ST 09052 96269, with these values giving this hill 40.2m of drop which is sufficient for its inclusion to 100m Twmpau status.

The full details for the hill are:

Group:  Fforest Fawr

Name:  Goetre Coed

OS 1:50,000 map:  171

Summit Height:  165.9m (LIDAR)

Summit Grid Reference:  ST 09189 96517 (LIDAR)

Bwlch Height:  125.8m (LIDAR)

Bwlch Grid Reference:  ST 09052 96269 (LIDAR)

Drop:  40.2m (LIDAR)

Myrddyn Phillips (March 2019)