Mapping Mountains – Hill Reclassifications – 200m Twmpau

Pt. 254.9m (SH 690 175) – 200m Sub-Twmpau addition

There has been confirmation of an addition to the 200m Twmpau list due to LIDAR analysis conducted by Myrddyn Phillips, with the criteria for this list being:

200m Twmpau - Welsh hills at and above 200m and below 300m in height with 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 and above 200m and below 300m in height with 20m and more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

This hill was not listed in the Hills to be surveyed sub list when the original Welsh P30 hills were published on Geoff Crowder’s v-g.me website as it did not meet the criteria then used for this category of hill; however this list has now been standardised and interpolated heights and drop values also included, resulting in this hill being listed with c 22m of drop, based on the 256m summit spot height that appears on the Ordnance Survey Interactive Coverage Map hosted on the Geograph website and an estimated bwlch height of c 234m based on bwlch contouring between 230m – 240m.

Extract from the Ordnance Survey Interactive Coverage Map hosted on the Geograph website

As the name of the ffridd taking in this hill’s summit has not been confirmed the hill is being listed by the point (Pt. 254.9m) notation and it is adjoined to the Cadair Idris group of hills, which are situated in the south-western part of North Wales (Region A, Sub-Region A3), and the hill is positioned with the A 493 road to its north and has the town of Dolgellau towards its east.

As the hill is not a part of designated open access land permission to visit should be sought, for those wishing to do so a public footpath crosses to the south of the summit and this can be accessed from open access land to the west.

The confirmation of the addition of this hill to 200m Sub-Twmpau status is due to LIDAR analysis conducted by Myrddyn Phillips.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

The 1m DTM LIDAR analysis gives the hill the following details:

Name:  Pt. 254.9m

Summit Height:  254.9m

Summit Grid Reference:  SH 69086 17596

Bwlch Height:  231.5m

Bwlch Grid Reference:  SH 68969 17478

Drop:  23.5m

 

LIDAR image of Pt. 254.9m

Therefore, the 254.9m LIDAR analysis for the summit position at SH 69086 17596 and the 231.5m LIDAR analysis for the bwlch position at SH 68969 17478 gives this hill 23.5m of drop, which confirms its addition to 200m Sub-Twmpau status.

The full details for the hill are:

Group:  Cadair Idris

Name:  Pt. 254.9m

OS 1:50,000 map:  124

Summit Height:  254.9m (LIDAR)

Summit Grid Reference:  SH 69086 17596 (LIDAR)

Bwlch Height:  231.5m (LIDAR)

Bwlch Grid Reference:  SH 68969 17478 (LIDAR)

Drop:  23.5m (LIDAR)

Myrddyn Phillips (June 2018)