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

 

Top Field (SJ 070 055) – Sub-Trichant reclassified to Trichant

There has been confirmation of a reclassification 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 confirmed by LIDAR analysis and a subsequent Trimble GeoXH 6000 survey conducted by Myrddyn Phillips. 

Top Field (SJ 070 055)

The criteria for the list 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 13^th May 2017. 

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

The name the hill is listed by is Top 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 the A458 road further to its north and the B4389 road further to its east, and has the small town of Llanfair Caereinion towards the east north-east. 

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 Hills to be surveyed sub list that accompanied the main P30 list, as it was considered not to meet the criteria then used for the main P30 category. 

When the P30 lists were standardised, and interpolated heights and drop values also included, this hill was listed with an estimated c 32m of drop based on the 335m summit spot height and an estimated c 303m bwlch height based on interpolation of 10m contouring 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 Top Field (SJ 070 055) 

The result produced by LIDAR analysis gives this hill 32.0m of drop with a summit height of 333.1m, 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 Top Field

Therefore, the confirmation of the reclassification of this hill from Sub-Trichant status is due to LIDAR analysis and a Trimble GeoXH 6000 survey, resulting in a 333.3m summit height and a 301.1m bwlch height, with these values giving this hill 32.2m of drop, which is sufficient for it to be classified as a Trichant.

 

The full details for the hill are: 

Group:  Carnedd Wen 

Name:  Top Field 

OS 1:50,000 map:  125

Summit Height:  333.3m (converted to OSGM15, Trimble GeoXH 6000)                                          

Summit Grid Reference:  SJ 07082 05572 (Trimble GeoXH 6000) 

Bwlch Height:  301.1m (LIDAR) 

Bwlch Grid Reference:  SJ 06237 05273 (LIDAR) 

Drop:  32.2m (Trimble GeoXH 6000 summit and LIDAR bwlch) 

 

Myrddyn Phillips (March 2021)