Mapping Mountains – Hill Reclassifications – 100m Twmpau

Tal y Garreg (SH 574 035) – 100m Sub-Twmpau addition

There has been confirmation of an addition to the 100m Twmpau due to LIDAR analysis conducted by Myrddyn Phillips, with the criteria for this list being:

100m Twmpau - Welsh hills at and 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 and above 100m and below 200m 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 did not appear in the accompanying 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 for this sub category; however this sub list has now been standardised and interpolated heights also included.

When this sub list was standardised and interpolated heights also included this hill was listed with an estimated c 21m of drop, based on the 178m height given to a triangulation pillar at the summit and an estimated bwlch height of c 157m based on bwlch contouring between 150m – 160m.

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

The name of the hill is Tal y Garreg 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 between the coast to its west and the Afon Dysynni to its south and has the small community of Tywyn towards the south- south-east.

If wanting to visit the hill an ascent can start from either the south or north of its summit following public footpaths and bridleways, with one of the former passing over its high point.

The confirmation of the addition of Tal y Garreg to 100m 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:

Tal y Garreg

Summit Height:  177.3m

Summit Grid Reference:  SH 57402 03580 and SH 57401 03579

Bwlch Height:  156.8m

Bwlch Grid Reference:  SH 57558 03762

Drop:  20.6m

 

LIDAR image of Tal y Garreg

Therefore, the 177.3m LIDAR analysis for the summit position at SH 57402 03580 and SH 57401 03579 and the 156.8m LIDAR analysis for the bwlch position at SH 57558 03762 gives this hill 20.6m of drop, which confirms its addition to 100 Sub-Twmpau status.

The full details for the hill are:

Group:  Cadair Idris

Name:  Tal y Garreg

OS 1:50,000 map:  124

Summit Height:  177.3m (LIDAR)

Summit Grid Reference:  SH 57402 03580 and SH 57401 03579 (LIDAR)

Bwlch Height:  156.8m (LIDAR)

Bwlch Grid Reference:  SH 57558 03762 (LIDAR)

Drop:  20.6m

Myrddyn Phillips (May 2018)