Mapping Mountains – Hill Reclassifications – 500m Twmpau

Mynydd Pen y Cae (SN 887 032) – 500m Sub-Twmpau deletion

There has been a deletion of a hill that is listed in the 500m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by a survey with the Trimble GeoXH 6000 conducted by Myrddyn Phillips with assistance from Aled Williams which took place on the 22^nd June 2019.

Mynydd Pen y Cae (SN 887 032)

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

500m Twmpau - Welsh hills at or above 500m and below 600m in height with 30m minimum drop, with an accompanying sub list entitled the 500m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 500m and below 600m 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 Mynydd Pen y Cae, 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 positioned with the A465 road and Cwm Nedd (Vale of Neath) to its north-west and the A4061 road to its east, and has the small town of Glyn-nedd (Glynneath) to the north. 

Prior to the survey with the Trimble GeoXH 6000 this hill was listed with an estimated c 20m of drop based on the 573m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated bwlch height of c 553m based on 10m contouring between 550m – 560m.

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 as its summit spot height and bwlch contouring remained the same, so did the estimated c 20m drop value.

The area taking in this hill was re-examined when the OS Maps website became available online.  This is the replacement for OS Get-a-map and has contours at 5m intervals.  This mapping shows the bwlch contouring between 555m – 560m with interpolation placing the bwlch height as an estimated c 557m which when coupled with the 573m summit spot height on the 1:25,000 Explorer map gives this hill c 16m of drop.

Extract from the OS Maps website

The deletion of Mynydd Pen y Cae from 500m Sub-Twmpau status is due to a survey with the Trimble GeoXH 6000, resulting in a 574.6m summit height and a 557.0m bwlch height, with the latter in accordance with the 5m contouring on the OS Maps website, with these values giving this hill 17.6m of drop which is insufficient for its continued classification as a 500m Sub-Twmpau.

The Trimble GeoXH 6000 gathering data at the summit of Mynydd Pen y Cae

The Trimble GeoXH 6000 gathering data at the bwlch of Mynydd Pen y Cae

The full details for the hill are:

Group:  Cymoedd Morgannwg

Name:  Mynydd Pen y Cae

OS 1:50,000 map:  170

Summit Height:  574.6m (converted to OSGM15)

Summit Grid Reference:  SN 88743 03214

Bwlch Height:  557.0m (converted to OSGM15)

Bwlch Grid Reference:  SN 89494 03481

Drop:  17.6m

For details on the survey of this hill

Myrddyn Phillips (September 2019)