Mapping Mountains – Hill Reclassifications – Y Trichant – The 300m Hills of Wales

 

Gribin (SJ 215 470) – Sub-Trichant addition

There has been confirmation of an addition to the list of Y Trichant – The 300m Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Gribin (SJ 215 470)

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

Y Trichant – The 300m Hills of Wales – Welsh hills at or above 300m and below 400m in height that have 30m minimum drop, with an accompanying sub list entitled the Sub-Trichant, with the criteria for this sub category being all Welsh hills at or above 300m and below 400m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the Introduction to the list and the renaming of it appearing on Mapping Mountains on the 13^th May 2017. 

Y Trichant - The 300m Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Gribin, and it is adjoined to the Moel y Gamelin group of hills, which are situated in the north-eastern part of North Wales (Region A, Sub-Region A2), and it is positioned with minor roads to its west, south and east, with the A542 road further to its west, and has the town of Llangollen towards the south. 

When the original 300m height band of Welsh P30 hills was published on Geoff Crowder’s v-g.me website, this hill was not included in the Hills to be surveyed sub list that accompanied the main P30 list, as it was considered not to meet the criteria then used for this sub category. 

After the P30 lists were standardised, and interpolated heights and drop values also included, this hill was listed with an estimated c 23m of drop based on the 340m summit spot height and an estimated c 317m bwlch height based on interpolation of 5m contouring between 315m – 320m 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. 

Therefore, the confirmation of the addition of this hill to Sub-Trichant status is due to LIDAR analysis, resulting in a 339.7m summit height and a 316.45m bwlch height, with these values giving this hill 23.3m of drop, which is sufficient for it to be classified as a Sub-Trichant.

 

The full details for the hill are: 

Group:  Moel y Gamelin 

Name:  Gribin 

OS 1:50,000 map:  117

Summit Height:  339.7m (LIDAR)                                                           

Summit Grid Reference:  SJ 21574 47010 (LIDAR) 

Bwlch Height:  316.45m (LIDAR) 

Bwlch Grid Reference:  SJ 21643 47160 (LIDAR) 

Drop:  23.3m (LIDAR) 

 

Myrddyn Phillips (February 2021)

 

 

 

 

 

Mapping Mountains – Hill Reclassifications – 200m Twmpau

Gribin (SH 675 168) – 200m Sub-Twmpau reclassified to 200m Twmpau

There has been confirmation of a reclassification 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 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 was thought not  to meet the criteria then used for the main P30 list; however this list has now been standardised and interpolated heights and drop values also included, resulting in this hill being listed with an estimated c 39m of drop, based on an estimated c 211m summit height and an estimated bwlch height of c 172m based on bwlch map contouring between 170m – 180m.  The details for this hill were later amended when the Ordnance Survey Interactive Coverage Map hosted on the Geograph website became available online and it was then listed with a 211m summit height based on the spot height appearing on this map.

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

The name of the hill is Gribin 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), it is positioned overlooking the A 493 road which is to its north and has the small community of Arthog towards the south-west and the town of Dolgellau towards the east.

The summit and upper southern section of the hill is a part of designated open access land and a public footpath leads toward this from the west south-west of the hill, with another option for an ascent following a public footpath from the north-east of the hill.

The confirmation of the reclassification of Gribin to 200m 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:  Gribin

Summit Height:  209.3m

Summit Grid Reference:  SH 67559 16814

Bwlch Height:  169.7m

Bwlch Grid Reference:  SH 67588 16670

Drop:  39.6m

LIDAR image of Gribin

Therefore, the 209.3m LIDAR analysis for the summit position at SH 67559 16814 and the 169.7m LIDAR analysis for the bwlch position at SH 67588 16670 gives this hill 39.6m of drop, which confirms its reclassification to 200m Twmpau status.

The full details for the hill are:

Group:  Cadair Idris

Name:  Gribin

OS 1:50,000 map:  124

Summit Height:  209.3m (LIDAR)

Summit Grid Reference:  SH 67559 16814 (LIDAR)

Bwlch Height:  169.7m (LIDAR)

Bwlch Grid Reference:  SH 67588 16670 (LIDAR)

Drop:  39.6m (LIDAR)

Myrddyn Phillips (May 2018)