Mapping Mountains – Hill Reclassifications – 200m Twmpau

Pastures (SJ 080 032) – 200m Sub-Twmpau addition

There has been confirmation of an addition to the list of 200m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis and a subsequent Trimble GeoXH 6000 survey conducted by Myrddyn Phillips.

Pastures (SJ 080 032)

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

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 200m and below 300m 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 200m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Pastures and this was derived from local enquiry, and it is adjoined to the Carnedd Wen group of hills which are situated in the south-eastern part of North Wales (Region A, Sub-Region A4), and it is encircled by minor roads, with the A458 road further to the north, the B4389 road further to the east and the A470 road further to the south-west, and has the small town of Llanfair Caereinion towards the north-east.

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was not included in the accompanying Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category. 

When the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-assessed and it was listed with 28m of drop, based on the 289m summit spot height and the 261m bwlch spot height that appear on the Ordnance Survey 1:25,000 Explorer map.

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

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 image of Pastures

The result produced by LIDAR analysis gives this hill 27.8m of drop, and as the summit has now been surveyed with the Trimble GeoXH 6000 it is this result that is being prioritised for listing purposes.

The Trimble GeoXH 6000 gathering data at the summit of the Pastures

Therefore, the confirmation of the addition of this hill to 200m Sub-Twmpau status is due to LIDAR analysis and a Trimble GeoXH 6000 survey, resulting in a 288.5m summit height and a 260.5m bwlch height, with these values giving this hill 27.9m of drop, which is sufficient for it to be classified as a 200m Sub-Twmpau.

The full details for the hill are:

Group:  Carnedd Wen

Name:  Pastures

OS 1:50,000 map:  136

Summit Height:  288.5m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SJ 08047 03297 (Trimble GeoXH 6000)

Bwlch Height:  260.5m (LIDAR)

Bwlch Grid Reference:  SJ 07733 03319 (LIDAR)

Drop:  27.9m (Trimble GeoXH 6000 summit and LIDAR bwlch)

For details on the Trimble GeoXH 6000 survey of this hill

Myrddyn Phillips (December 2020)