Mapping Mountains – Hill Reclassifications – Y Trichant – The 300m Hills of Wales and 200m Twmpau

Square Field (SJ 070 031) – Trichant reclassified to 200m Twmpau

There has been a reclassification to the list of Y Trichant – The 300m Hills of Wales and the 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.

Square Field (SJ 070 031)

The criteria for the two listings that this reclassification 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 13th May 2017.

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

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 being listed by is Square Field 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 also the A458 road to its north, the A470 road to its south-west and the B4389 road to its east, and has the village of Adfa towards the south south-west.

When the original 300m height band of Welsh P30 hills was published on Geoff Crowder’s v-g.me website, this hill was included in the main P30 list and listed with a 300m summit height, based on the spot height that appears 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 Square Field (SJ 070 031)

The result produced by LIDAR analysis gives this hill a 299.4m summit height, 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 Square Field

Therefore, the confirmation of the reclassification of this hill from Trichant status is due to LIDAR analysis and a Trimble GeoXH 6000 survey, resulting in 45.8m of drop, with a 299.4m summit height and a 253.6m bwlch height, with the summit height insufficient for Trichant status the therefore the hill is reclassified to a 200m Twmpau

The full details for the hill are:

Group:  Carnedd Wen

Name:  Square Field

OS 1:50,000 map:  136

Summit Height:  299.4m (converted to OSGM15, Trimble GeoXH 6000)

                                                           

Summit Grid Reference:  SJ 07034 03161 (Trimble GeoXH 6000)

Bwlch Height:  253.6m (LIDAR)

Bwlch Grid Reference:  SJ 06533 03161 (LIDAR)

Drop:  45.8m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Myrddyn Phillips (November 2020)